[PATCH v4 00/24] Tracefs support for pKVM

[PATCH v4 00/24] Tracefs support for pKVM

[Vincent Donnefort]

The growing set of features supported by the hypervisor in protected
mode necessitates debugging and profiling tools. Tracefs is the
ideal candidate for this task:

  * It is simple to use and to script.

  * It is supported by various tools, from the trace-cmd CLI to the
    Android web-based perfetto.

  * The ring-buffer, where are stored trace events consists of linked
    pages, making it an ideal structure for sharing between kernel and
    hypervisor.

This series first introduces a new generic way of creating remote events and
remote buffers. Then it adds support to the pKVM hypervisor.

1. ring-buffer
--------------

To setup the per-cpu ring-buffers, a new interface is created:

  ring_buffer_remote:	Describes what the kernel needs to know about the
			remote writer, that is, the set of pages forming the
			ring-buffer and a callback for the reader/head
			swapping (enables consuming read)

  ring_buffer_remote():	Creates a read-only ring-buffer from a
			ring_buffer_remote.

To keep the internals of `struct ring_buffer` in sync with the remote,
the meta-page is used. It was originally introduced to enable user-space
mapping of the ring-buffer [1]. In this case, the kernel is not the
producer anymore but the reader. The function to read that meta-page is:

  ring_buffer_poll_remote():
			Update `struct ring_buffer` based on the remote
			meta-page. Wake-up readers if necessary.

The kernel has to poll the meta-page to be notified of newly written
events.

2. Tracefs
----------

This series introduce a new trace_remote that does the link between
tracefs and the remote ring-buffer.

The interface is found in the remotes/ directory at the root of the
tracefs mount point. Each remote is like an instance and you'll find
there a subset of the regular Tracefs user-space interface:

  remotes/test/
     buffer_size_kb
     trace_clock
     trace_pipe
     trace
     per_cpu/
             cpuX/
                 trace
                 trace_pipe
     events/

            test/
                selftest/
                          enable
                          id

Behind the scenes, kernel/trace/trace_remote.c creates this tracefs
hierarchy without relying on kernel/trace/trace.c. This is due to
fundamental differences:

  * Remote tracing doesn't support trace_array's system-specific
    features (snapshots, tracers, etc.).

  * Logged event formats differ (e.g., no PID for remote events).

  * Buffer operations require specific remote interactions.

3. Simple Ring-Buffer
---------------------

As the current ring-buffer.c implementation has too many dependencies to
be used directly by the pKVM hypervisor. A new simple implementation is
created and can be found in kernel/trace/simple-ring-buffer.c.

This implementation is write-only and is used by both the pKVM
hypervisor and a trace_remote test module.

4. Events
---------

A new REMOTE_EVENT() macro is added to simplify the creation of events
on the kernel side. As remote tracing buffer are read only, only the
event structure and a way of printing must be declared. The prototype of
the macro is very similar to the well-known TRACE_EVENT()

 REMOTE_EVENT(my_event, id,
     RE_STRUCT(
         re_field(u64, foobar)
     ),
     RE_PRINTK("foobar=%lld", __entry->foobar)
     )
  )

5. pKVM
-------

The pKVM support simply creates a "hypervisor" trace_remote on the
kernel side and inherits from simple-ring-buffer.c on the hypervisor
side.

A new event macro is created HYP_EVENT() that is under the hood re-using
REMOTE_EVENT() (defined in the previous paragaph) as well as generate
hypervisor specific struct and trace_<event>() functions.

5. Limitations:
---------------

Non-consuming reading of the buffer isn't supported (i.e. cat trace ->
-EPERM) due to current the lack of support in the ring-buffer meta-page.

[1] https://tracingsummit.org/ts/2022/hypervisortracing/
[2] https://lore.kernel.org/all/20240510140435.3550353-1-vdonnefort@google.com/

Changes since v3 (https://lore.kernel.org/all/20250224121353.98697-1-vdonnefort@google.com/)

  - Move tracefs support from kvm/hyp_trace.c into a generic trace_remote.c.
  - Move ring-buffer implementation from nvhe/trace.c into  a generic
    simple-ring-buffer.c
  - Rebase on 6.15-rc4.

Changes since v2 (https://lore.kernel.org/all/20250108114536.627715-1-vdonnefort@google.com/)

  - Fix ring-buffer remote reset
  - Fix fast-forward in rb_page_desc()
  - Refactor nvhe/trace.c
  - struct hyp_buffer_page more compact
  - Add a struct_len to trace_page_desc
  - Extend reset testing
  - Rebase on 6.14-rc3

Changes since v1 (https://lore.kernel.org/all/20240911093029.3279154-1-vdonnefort@google.com/)

  - Add 128-bits mult fallback in the unlikely event of an overflow. (John)
  - Fix ELF section sort.
  - __always_inline trace_* event macros.
  - Fix events/<event>/enable permissions.
  - Rename ring-buffer "writer" to "remote".
  - Rename CONFIG_PROTECTED_NVHE_TESTING to PKVM_SELFTEST to align with
    Quentin's upcoming selftest
  - Rebase on 6.13-rc3.

Changes since RFC (https://lore.kernel.org/all/20240805173234.3542917-1-vdonnefort@google.com/)

  - hypervisor trace clock:
     - mult/shift computed in hyp_trace.c. (John)
     - Update clock when it deviates from kernel boot clock. (John)
     - Add trace_clock file.
     - Separate patch for better readability.
  - Add a proper reset interface which does not need to teardown the
    tracing buffers. (Steven)
  - Return -EPERM on trace access. (Steven)
  - Add per-cpu trace file.
  - Automatically teardown and free the tracing buffer when it is empty,
    without readers and not currently tracing.
  - Show in buffer_size_kb if the buffer is loaded in the hypervisor or
    not.
  - Extend tests to cover reset and unload.
  - CC timekeeping folks on relevant patches (Marc)

Vincent Donnefort (24):
  ring-buffer: Introduce ring-buffer remotes
  tracing: Introduce trace remotes
  tracing: Add reset to trace remotes
  tracing: Add init callback to trace remotes
  tracing: Add events to trace remotes
  tracing: Add events/ root files to trace remotes
  tracing: Add helpers to create trace remote events
  ring-buffer: Expose buffer_data_page material
  tracing: Introduce simple_ring_buffer
  tracing: Add a trace remote module for testing
  tracing: selftests: Add trace remote tests
  tracing: load/unload page callbacks for simple_ring_buffer
  tracing: Check for undefined symbols in simple_ring_buffer
  KVM: arm64: Support unaligned fixmap in the nVHE hyp
  KVM: arm64: Add .hyp.data section
  KVM: arm64: Add clock support for the pKVM hyp
  KVM: arm64: Add tracing capability for the pKVM hyp
  KVM: arm64: Add trace remote for the pKVM hyp
  KVM: arm64: Sync boot clock with the pKVM hyp
  KVM: arm64: Add trace reset to the pKVM hyp
  KVM: arm64: Add event support to the pKVM hyp and trace remote
  KVM: arm64: Add hyp_enter/hyp_exit events to pKVM hyp
  KVM: arm64: Add selftest event support to pKVM hyp
  tracing: selftests: Add pKVM trace remote tests

 arch/arm64/include/asm/kvm_asm.h              |   8 +
 arch/arm64/include/asm/kvm_define_hypevents.h |  21 +
 arch/arm64/include/asm/kvm_hyp.h              |   1 -
 arch/arm64/include/asm/kvm_hypevents.h        |  41 +
 arch/arm64/include/asm/kvm_hyptrace.h         |  26 +
 arch/arm64/include/asm/sections.h             |   1 +
 arch/arm64/kernel/image-vars.h                |   6 +
 arch/arm64/kernel/vmlinux.lds.S               |  36 +-
 arch/arm64/kvm/Kconfig                        |  18 +
 arch/arm64/kvm/Makefile                       |   2 +
 arch/arm64/kvm/arm.c                          |  11 +
 arch/arm64/kvm/hyp/include/nvhe/arm-smccc.h   |  13 +
 arch/arm64/kvm/hyp/include/nvhe/clock.h       |  16 +
 .../kvm/hyp/include/nvhe/define_events.h      |  21 +
 arch/arm64/kvm/hyp/include/nvhe/trace.h       |  59 ++
 arch/arm64/kvm/hyp/nvhe/Makefile              |   1 +
 arch/arm64/kvm/hyp/nvhe/clock.c               |  65 ++
 arch/arm64/kvm/hyp/nvhe/events.c              |  36 +
 arch/arm64/kvm/hyp/nvhe/ffa.c                 |   2 +-
 arch/arm64/kvm/hyp/nvhe/hyp-main.c            |  86 ++
 arch/arm64/kvm/hyp/nvhe/hyp.lds.S             |   8 +
 arch/arm64/kvm/hyp/nvhe/mm.c                  |   2 +-
 arch/arm64/kvm/hyp/nvhe/psci-relay.c          |   5 +-
 arch/arm64/kvm/hyp/nvhe/setup.c               |   4 +
 arch/arm64/kvm/hyp/nvhe/switch.c              |   5 +-
 arch/arm64/kvm/hyp/nvhe/trace.c               | 286 ++++++
 arch/arm64/kvm/hyp_trace.c                    | 385 ++++++++
 arch/arm64/kvm/hyp_trace.h                    |  11 +
 arch/arm64/kvm/pkvm.c                         |   1 +
 include/linux/ring_buffer.h                   | 102 +-
 include/linux/simple_ring_buffer.h            |  57 ++
 include/linux/trace_remote.h                  |  27 +
 include/linux/trace_remote_event.h            |  33 +
 include/trace/define_remote_events.h          |  73 ++
 kernel/trace/Kconfig                          |  14 +
 kernel/trace/Makefile                         |  19 +
 kernel/trace/remote_test.c                    | 259 +++++
 kernel/trace/remote_test_events.h             |  10 +
 kernel/trace/ring_buffer.c                    | 254 ++++-
 kernel/trace/simple_ring_buffer.c             | 404 ++++++++
 kernel/trace/trace.c                          |   2 +-
 kernel/trace/trace.h                          |   6 +
 kernel/trace/trace_remote.c                   | 920 ++++++++++++++++++
 .../ftrace/test.d/remotes/buffer_size.tc      |  24 +
 .../selftests/ftrace/test.d/remotes/functions |  33 +
 .../ftrace/test.d/remotes/pkvm/buffer_size.tc |  10 +
 .../ftrace/test.d/remotes/pkvm/reset.tc       |  10 +
 .../ftrace/test.d/remotes/pkvm/trace_pipe.tc  |  10 +
 .../ftrace/test.d/remotes/pkvm/unloading.tc   |  10 +
 .../selftests/ftrace/test.d/remotes/reset.tc  | 105 ++
 .../ftrace/test.d/remotes/trace_pipe.tc       |  57 ++
 .../ftrace/test.d/remotes/unloading.tc        |  36 +
 52 files changed, 3599 insertions(+), 53 deletions(-)
 create mode 100644 arch/arm64/include/asm/kvm_define_hypevents.h
 create mode 100644 arch/arm64/include/asm/kvm_hypevents.h
 create mode 100644 arch/arm64/include/asm/kvm_hyptrace.h
 create mode 100644 arch/arm64/kvm/hyp/include/nvhe/arm-smccc.h
 create mode 100644 arch/arm64/kvm/hyp/include/nvhe/clock.h
 create mode 100644 arch/arm64/kvm/hyp/include/nvhe/define_events.h
 create mode 100644 arch/arm64/kvm/hyp/include/nvhe/trace.h
 create mode 100644 arch/arm64/kvm/hyp/nvhe/clock.c
 create mode 100644 arch/arm64/kvm/hyp/nvhe/events.c
 create mode 100644 arch/arm64/kvm/hyp/nvhe/trace.c
 create mode 100644 arch/arm64/kvm/hyp_trace.c
 create mode 100644 arch/arm64/kvm/hyp_trace.h
 create mode 100644 include/linux/simple_ring_buffer.h
 create mode 100644 include/linux/trace_remote.h
 create mode 100644 include/linux/trace_remote_event.h
 create mode 100644 include/trace/define_remote_events.h
 create mode 100644 kernel/trace/remote_test.c
 create mode 100644 kernel/trace/remote_test_events.h
 create mode 100644 kernel/trace/simple_ring_buffer.c
 create mode 100644 kernel/trace/trace_remote.c
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/functions
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/pkvm/buffer_size.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/pkvm/reset.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/pkvm/trace_pipe.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/pkvm/unloading.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/reset.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/unloading.tc


base-commit: 02ddfb981de88a2c15621115dd7be2431252c568
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 01/24] ring-buffer: Introduce ring-buffer remotes

[Vincent Donnefort]

A ring-buffer remote is an entity outside of the kernel (most likely a
firmware or a hypervisor) capable of writing events in a ring-buffer
following the same format as the tracefs ring-buffer.

To setup the ring-buffer on the kernel side, a description of the pages
forming the ring-buffer (struct trace_buffer_desc) must be given.
Callbacks (swap_reader_page and reset) must also be provided.

It is expected from the remote to keep the meta-page updated.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 56e27263acf8..c0c7f8a0dcb3 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -248,4 +248,67 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 		    struct vm_area_struct *vma);
 int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
 int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
+
+#define meta_pages_lost(__meta) \
+	((__meta)->Reserved1)
+#define meta_pages_touched(__meta) \
+	((__meta)->Reserved2)
+
+struct ring_buffer_desc {
+	int		cpu;
+	unsigned int	nr_page_va; /* excludes the meta page */
+	unsigned long	meta_va;
+	unsigned long	page_va[];
+};
+
+struct trace_buffer_desc {
+	int		nr_cpus;
+	size_t		struct_len;
+	char		__data[]; /* list of ring_buffer_desc */
+};
+
+static inline struct ring_buffer_desc *__next_ring_buffer_desc(struct ring_buffer_desc *desc)
+{
+	size_t len = struct_size(desc, page_va, desc->nr_page_va);
+
+	return (struct ring_buffer_desc *)((void *)desc + len);
+}
+
+static inline struct ring_buffer_desc *__first_ring_buffer_desc(struct trace_buffer_desc *desc)
+{
+	return (struct ring_buffer_desc *)(&desc->__data[0]);
+}
+
+static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned int nr_cpus)
+{
+	unsigned int nr_pages = (PAGE_ALIGN(buffer_size) / PAGE_SIZE) + 1;
+	struct ring_buffer_desc *rbdesc;
+
+	return size_add(offsetof(struct trace_buffer_desc, __data),
+			size_mul(nr_cpus, struct_size(rbdesc, page_va, nr_pages)));
+}
+
+#define for_each_ring_buffer_desc(__pdesc, __cpu, __trace_pdesc)		\
+	for (__pdesc = __first_ring_buffer_desc(__trace_pdesc), __cpu = 0;	\
+	     __cpu < (__trace_pdesc)->nr_cpus;					\
+	     __cpu++, __pdesc = __next_ring_buffer_desc(__pdesc))
+
+struct ring_buffer_remote {
+	struct trace_buffer_desc	*desc;
+	int				(*swap_reader_page)(unsigned int cpu, void *priv);
+	int				(*reset)(unsigned int cpu, void *priv);
+	void				*priv;
+};
+
+int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu);
+
+struct trace_buffer *
+__ring_buffer_alloc_remote(struct ring_buffer_remote *remote,
+			   struct lock_class_key *key);
+
+#define ring_buffer_remote(remote)				\
+({								\
+	static struct lock_class_key __key;			\
+	__ring_buffer_alloc_remote(remote, &__key);		\
+})
 #endif /* _LINUX_RING_BUFFER_H */
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index c0f877d39a24..a96a0b231fee 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -523,6 +523,8 @@ struct ring_buffer_per_cpu {
 	struct trace_buffer_meta	*meta_page;
 	struct ring_buffer_cpu_meta	*ring_meta;
 
+	struct ring_buffer_remote	*remote;
+
 	/* ring buffer pages to update, > 0 to add, < 0 to remove */
 	long				nr_pages_to_update;
 	struct list_head		new_pages; /* new pages to add */
@@ -545,6 +547,8 @@ struct trace_buffer {
 
 	struct ring_buffer_per_cpu	**buffers;
 
+	struct ring_buffer_remote	*remote;
+
 	struct hlist_node		node;
 	u64				(*clock)(void);
 
@@ -2196,6 +2200,41 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	return -ENOMEM;
 }
 
+static struct ring_buffer_desc *ring_buffer_desc(struct trace_buffer_desc *trace_desc, int cpu)
+{
+	struct ring_buffer_desc *desc, *end;
+	size_t len;
+	int i;
+
+	if (!trace_desc)
+		return NULL;
+
+	if (cpu >= trace_desc->nr_cpus)
+		return NULL;
+
+	end = (struct ring_buffer_desc *)((void *)trace_desc + trace_desc->struct_len);
+	desc = __first_ring_buffer_desc(trace_desc);
+	len = struct_size(desc, page_va, desc->nr_page_va);
+	desc = (struct ring_buffer_desc *)((void *)desc + (len * cpu));
+
+	if (desc < end && desc->cpu == cpu)
+		return desc;
+
+	/* Missing CPUs, need to linear search */
+	for_each_ring_buffer_desc(desc, i, trace_desc) {
+		if (desc->cpu == cpu)
+			return desc;
+	}
+
+	return NULL;
+}
+
+static void *ring_buffer_desc_page(struct ring_buffer_desc *desc, int page_id)
+{
+	return page_id > desc->nr_page_va ? NULL : (void *)desc->page_va[page_id];
+}
+
+
 static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 			     unsigned long nr_pages)
 {
@@ -2256,6 +2295,30 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 
 	cpu_buffer->reader_page = bpage;
 
+	if (buffer->remote) {
+		struct ring_buffer_desc *desc = ring_buffer_desc(buffer->remote->desc, cpu);
+
+		if (!desc)
+			goto fail_free_reader;
+
+		cpu_buffer->remote = buffer->remote;
+		cpu_buffer->meta_page = (struct trace_buffer_meta *)(void *)desc->meta_va;
+		cpu_buffer->subbuf_ids = desc->page_va;
+		cpu_buffer->nr_pages = desc->nr_page_va - 1;
+		atomic_inc(&cpu_buffer->record_disabled);
+		atomic_inc(&cpu_buffer->resize_disabled);
+
+		bpage->page = ring_buffer_desc_page(desc, cpu_buffer->meta_page->reader.id);
+		if (!bpage->page)
+			goto fail_free_reader;
+		/*
+		 * The meta-page can only describe which of the ring-buffer page
+		 * is the reader. There is no need to init the rest of the
+		 * ring-buffer.
+		 */
+		return cpu_buffer;
+	}
+
 	if (buffer->range_addr_start) {
 		/*
 		 * Range mapped buffers have the same restrictions as memory
@@ -2333,6 +2396,10 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 
 	irq_work_sync(&cpu_buffer->irq_work.work);
 
+	/* remote ring-buffer. We do not own the data pages */
+	if (cpu_buffer->remote)
+		cpu_buffer->reader_page->page = NULL;
+
 	free_buffer_page(cpu_buffer->reader_page);
 
 	if (head) {
@@ -2355,7 +2422,8 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 					 int order, unsigned long start,
 					 unsigned long end,
 					 unsigned long scratch_size,
-					 struct lock_class_key *key)
+					 struct lock_class_key *key,
+					 struct ring_buffer_remote *remote)
 {
 	struct trace_buffer *buffer;
 	long nr_pages;
@@ -2383,6 +2451,11 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 	buffer->flags = flags;
 	buffer->clock = trace_clock_local;
 	buffer->reader_lock_key = key;
+	if (remote) {
+		buffer->remote = remote;
+		/* The writer is remote. This ring-buffer is read-only */
+		atomic_inc(&buffer->record_disabled);
+	}
 
 	init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
 	init_waitqueue_head(&buffer->irq_work.waiters);
@@ -2502,7 +2575,7 @@ struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
 					struct lock_class_key *key)
 {
 	/* Default buffer page size - one system page */
-	return alloc_buffer(size, flags, 0, 0, 0, 0, key);
+	return alloc_buffer(size, flags, 0, 0, 0, 0, key, NULL);
 
 }
 EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
@@ -2529,7 +2602,18 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
 					       struct lock_class_key *key)
 {
 	return alloc_buffer(size, flags, order, start, start + range_size,
-			    scratch_size, key);
+			    scratch_size, key, NULL);
+}
+
+/**
+ * __ring_buffer_alloc_remote - allocate a new ring_buffer from a remote
+ * @remote: Contains a description of the ring-buffer pages and remote callbacks.
+ * @key: ring buffer reader_lock_key.
+ */
+struct trace_buffer *__ring_buffer_alloc_remote(struct ring_buffer_remote *remote,
+						struct lock_class_key *key)
+{
+	return alloc_buffer(0, 0, 0, 0, 0, 0, key, remote);
 }
 
 void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size)
@@ -5278,8 +5362,56 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
 	}
 }
 
+static bool rb_read_remote_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	local_set(&cpu_buffer->entries, READ_ONCE(cpu_buffer->meta_page->entries));
+	local_set(&cpu_buffer->overrun, READ_ONCE(cpu_buffer->meta_page->overrun));
+	local_set(&cpu_buffer->pages_touched, READ_ONCE(meta_pages_touched(cpu_buffer->meta_page)));
+	local_set(&cpu_buffer->pages_lost, READ_ONCE(meta_pages_lost(cpu_buffer->meta_page)));
+	/*
+	 * No need to get the "read" field, it can be tracked here as any
+	 * reader will have to go through a rign_buffer_per_cpu.
+	 */
+
+	return rb_num_of_entries(cpu_buffer);
+}
+
 static struct buffer_page *
-rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
+__rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	u32 prev_reader;
+
+	if (!rb_read_remote_meta_page(cpu_buffer))
+		return NULL;
+
+	/* More to read on the reader page */
+	if (cpu_buffer->reader_page->read < rb_page_size(cpu_buffer->reader_page)) {
+		if (!cpu_buffer->reader_page->read)
+			cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
+		return cpu_buffer->reader_page;
+	}
+
+	prev_reader = cpu_buffer->meta_page->reader.id;
+
+	WARN_ON(cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu, cpu_buffer->remote->priv));
+	/* nr_pages doesn't include the reader page */
+	if (WARN_ON(cpu_buffer->meta_page->reader.id > cpu_buffer->nr_pages))
+		return NULL;
+
+	cpu_buffer->reader_page->page =
+		(void *)cpu_buffer->subbuf_ids[cpu_buffer->meta_page->reader.id];
+	cpu_buffer->reader_page->id = cpu_buffer->meta_page->reader.id;
+	cpu_buffer->reader_page->read = 0;
+	cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
+	cpu_buffer->lost_events = cpu_buffer->meta_page->reader.lost_events;
+
+	WARN_ON(prev_reader == cpu_buffer->meta_page->reader.id);
+
+	return rb_page_size(cpu_buffer->reader_page) ? cpu_buffer->reader_page : NULL;
+}
+
+static struct buffer_page *
+__rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	struct buffer_page *reader = NULL;
 	unsigned long bsize = READ_ONCE(cpu_buffer->buffer->subbuf_size);
@@ -5450,6 +5582,13 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
 	return reader;
 }
 
+static struct buffer_page *
+rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	return cpu_buffer->remote ? __rb_get_reader_page_from_remote(cpu_buffer) :
+				    __rb_get_reader_page(cpu_buffer);
+}
+
 static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	struct ring_buffer_event *event;
@@ -5854,7 +5993,7 @@ ring_buffer_read_prepare(struct trace_buffer *buffer, int cpu, gfp_t flags)
 	struct ring_buffer_per_cpu *cpu_buffer;
 	struct ring_buffer_iter *iter;
 
-	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+	if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->remote)
 		return NULL;
 
 	iter = kzalloc(sizeof(*iter), flags);
@@ -6024,6 +6163,23 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	struct buffer_page *page;
 
+	if (cpu_buffer->remote) {
+		if (!cpu_buffer->remote->reset)
+			return;
+
+		cpu_buffer->remote->reset(cpu_buffer->cpu, cpu_buffer->remote->priv);
+		rb_read_remote_meta_page(cpu_buffer);
+
+		/* Read related values, not covered by the meta-page */
+		local_set(&cpu_buffer->pages_read, 0);
+		cpu_buffer->read = 0;
+		cpu_buffer->read_bytes = 0;
+		cpu_buffer->last_overrun = 0;
+		cpu_buffer->reader_page->read = 0;
+
+		return;
+	}
+
 	rb_head_page_deactivate(cpu_buffer);
 
 	cpu_buffer->head_page
@@ -6259,6 +6415,49 @@ bool ring_buffer_empty_cpu(struct trace_buffer *buffer, int cpu)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
 
+int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags;
+
+	if (cpu != RING_BUFFER_ALL_CPUS) {
+		if (!cpumask_test_cpu(cpu, buffer->cpumask))
+			return -EINVAL;
+
+		cpu_buffer = buffer->buffers[cpu];
+
+		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+		if (rb_read_remote_meta_page(cpu_buffer))
+			rb_wakeups(buffer, cpu_buffer);
+		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+		return 0;
+	}
+
+	/*
+	 * Make sure all the ring buffers are up to date before we start reading
+	 * them.
+	 */
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+		rb_read_remote_meta_page(buffer->buffers[cpu]);
+		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+	}
+
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+		if (rb_num_of_entries(cpu_buffer))
+			rb_wakeups(buffer, buffer->buffers[cpu]);
+		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+	}
+
+	return 0;
+}
+
 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 /**
  * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
@@ -6510,6 +6709,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	unsigned int commit;
 	unsigned int read;
 	u64 save_timestamp;
+	bool force_memcpy;
 	int ret = -1;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
@@ -6547,6 +6747,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	/* Check if any events were dropped */
 	missed_events = cpu_buffer->lost_events;
 
+	force_memcpy = cpu_buffer->mapped || cpu_buffer->remote;
+
 	/*
 	 * If this page has been partially read or
 	 * if len is not big enough to read the rest of the page or
@@ -6556,7 +6758,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	 */
 	if (read || (len < (commit - read)) ||
 	    cpu_buffer->reader_page == cpu_buffer->commit_page ||
-	    cpu_buffer->mapped) {
+	    force_memcpy) {
 		struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
 		unsigned int rpos = read;
 		unsigned int pos = 0;
@@ -7138,7 +7340,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 	unsigned long flags, *subbuf_ids;
 	int err = 0;
 
-	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+	if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->remote)
 		return -EINVAL;
 
 	cpu_buffer = buffer->buffers[cpu];
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 02/24] tracing: Introduce trace remotes

[Vincent Donnefort]

A trace remote relies on ring-buffer remotes to read and control
compatible tracing buffers, written by entity such as firmware or
hypervisor.

Add a Tracefs directory remotes/ that contains all instances of trace
remotes. Each instance follows the same hierarchy as any other to ease
the support by existing user-space tools.

This currently does not provide any event support, which will come
later.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
new file mode 100644
index 000000000000..de043a6f2fe0
--- /dev/null
+++ b/include/linux/trace_remote.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_TRACE_REMOTE_H
+#define _LINUX_TRACE_REMOTE_H
+
+#include <linux/ring_buffer.h>
+
+struct trace_remote_callbacks {
+	struct trace_buffer_desc *
+		(*load_trace_buffer)(unsigned long size, void *priv);
+	void	(*unload_trace_buffer)(struct trace_buffer_desc *desc, void *priv);
+	int	(*enable_tracing)(bool enable, void *priv);
+	int	(*swap_reader_page)(unsigned int cpu, void *priv);
+};
+
+int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv);
+int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t size,
+			      const struct cpumask *cpumask);
+void trace_remote_free_buffer(struct trace_buffer_desc *desc);
+
+#endif
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index a3f35c7d83b6..2fcc86c7fe7e 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -1215,4 +1215,7 @@ config HIST_TRIGGERS_DEBUG
 
 source "kernel/trace/rv/Kconfig"
 
+config TRACE_REMOTE
+	bool
+
 endif # FTRACE
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 057cd975d014..b8204ae93744 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -110,4 +110,5 @@ obj-$(CONFIG_FPROBE_EVENTS) += trace_fprobe.o
 obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o
 obj-$(CONFIG_RV) += rv/
 
+obj-$(CONFIG_TRACE_REMOTE) += trace_remote.o
 libftrace-y := ftrace.o
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8ddf6b17215c..6ced57e089a9 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8839,7 +8839,7 @@ static struct dentry *tracing_dentry_percpu(struct trace_array *tr, int cpu)
 	return tr->percpu_dir;
 }
 
-static struct dentry *
+struct dentry *
 trace_create_cpu_file(const char *name, umode_t mode, struct dentry *parent,
 		      void *data, long cpu, const struct file_operations *fops)
 {
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 79be1995db44..f357e7e1ae71 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -670,6 +670,12 @@ struct dentry *trace_create_file(const char *name,
 				 struct dentry *parent,
 				 void *data,
 				 const struct file_operations *fops);
+struct dentry *trace_create_cpu_file(const char *name,
+				     umode_t mode,
+				     struct dentry *parent,
+				     void *data,
+				     long cpu,
+				     const struct file_operations *fops);
 
 int tracing_init_dentry(void);
 
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
new file mode 100644
index 000000000000..462c2d085a08
--- /dev/null
+++ b/kernel/trace/trace_remote.c
@@ -0,0 +1,517 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 - Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <linux/kstrtox.h>
+#include <linux/lockdep.h>
+#include <linux/mutex.h>
+#include <linux/tracefs.h>
+#include <linux/trace_remote.h>
+#include <linux/trace_seq.h>
+#include <linux/types.h>
+
+#include "trace.h"
+
+#define TRACEFS_DIR		"remotes"
+#define TRACEFS_MODE_WRITE	0640
+#define TRACEFS_MODE_READ	0440
+
+struct trace_remote_iterator {
+	struct trace_remote		*remote;
+	struct trace_seq		seq;
+	struct delayed_work		poll_work;
+	unsigned long			lost_events;
+	u64				ts;
+	int				cpu;
+	int				evt_cpu;
+};
+
+struct trace_remote {
+	struct trace_remote_callbacks	*cbs;
+	void				*priv;
+	struct trace_buffer		*trace_buffer;
+	struct trace_buffer_desc	*trace_buffer_desc;
+	unsigned long			trace_buffer_size;
+	struct ring_buffer_remote	rb_remote;
+	struct mutex			lock;
+	unsigned int			nr_readers;
+	unsigned int			poll_ms;
+	bool				tracing_on;
+};
+
+static bool trace_remote_loaded(struct trace_remote *remote)
+{
+	return remote->trace_buffer;
+}
+
+static bool trace_remote_busy(struct trace_remote *remote)
+{
+	return trace_remote_loaded(remote) &&
+		(remote->nr_readers || remote->tracing_on ||
+		 !ring_buffer_empty(remote->trace_buffer));
+}
+
+static int trace_remote_load(struct trace_remote *remote)
+{
+	struct ring_buffer_remote *rb_remote = &remote->rb_remote;
+
+	lockdep_assert_held(&remote->lock);
+
+	if (trace_remote_loaded(remote))
+		return 0;
+
+	remote->trace_buffer_desc = remote->cbs->load_trace_buffer(remote->trace_buffer_size,
+								   remote->priv);
+	if (!remote->trace_buffer_desc)
+		return -ENOMEM;
+
+	rb_remote->desc = remote->trace_buffer_desc;
+	rb_remote->swap_reader_page = remote->cbs->swap_reader_page;
+	rb_remote->priv = remote->priv;
+	remote->trace_buffer = ring_buffer_remote(rb_remote);
+	if (!remote->trace_buffer) {
+		remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void trace_remote_unload(struct trace_remote *remote)
+{
+	lockdep_assert_held(&remote->lock);
+
+	if (!trace_remote_loaded(remote) || trace_remote_busy(remote))
+		return;
+
+	ring_buffer_free(remote->trace_buffer);
+	remote->trace_buffer = NULL;
+	remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv);
+}
+
+static int trace_remote_start(struct trace_remote *remote)
+{
+	int ret;
+
+	lockdep_assert_held(&remote->lock);
+
+	if (remote->tracing_on)
+		return 0;
+
+	ret = trace_remote_load(remote);
+	if (ret)
+		return ret;
+
+	ret = remote->cbs->enable_tracing(true, remote->priv);
+	if (ret) {
+		trace_remote_unload(remote);
+		return ret;
+	}
+
+	remote->tracing_on = true;
+
+	return 0;
+}
+
+static int trace_remote_stop(struct trace_remote *remote)
+{
+	int ret;
+
+	lockdep_assert_held(&remote->lock);
+
+	if (!remote->tracing_on)
+		return 0;
+
+	ret = remote->cbs->enable_tracing(false, remote->priv);
+	if (ret)
+		return ret;
+
+	ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS);
+	remote->tracing_on = false;
+	trace_remote_unload(remote);
+
+	return 0;
+}
+
+static ssize_t
+tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_remote *remote = filp->private_data;
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+	if (ret)
+		return ret;
+
+	guard(mutex)(&remote->lock);
+
+	ret = val ? trace_remote_start(remote) : trace_remote_stop(remote);
+	if (ret)
+		return ret;
+
+	return cnt;
+}
+static int tracing_on_show(struct seq_file *s, void *unused)
+{
+	struct trace_remote *remote = s->private;
+
+	seq_printf(s, "%d\n", remote->tracing_on);
+
+	return 0;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(tracing_on);
+
+static ssize_t buffer_size_kb_write(struct file *filp, const char __user *ubuf, size_t cnt,
+				    loff_t *ppos)
+{
+	struct trace_remote *remote = filp->private_data;
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+	if (ret)
+		return ret;
+
+	/* KiB to Bytes */
+	if (!val || check_shl_overflow(val, 10, &val))
+		return -EINVAL;
+
+	guard(mutex)(&remote->lock);
+
+	remote->trace_buffer_size = val;
+
+	return cnt;
+}
+
+static int buffer_size_kb_show(struct seq_file *s, void *unused)
+{
+	struct trace_remote *remote = s->private;
+
+	seq_printf(s, "%lu (%s)\n", remote->trace_buffer_size >> 10,
+		   trace_remote_loaded(remote) ? "loaded" : "unloaded");
+
+	return 0;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(buffer_size_kb);
+
+static void __poll_remote(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct trace_remote_iterator *iter;
+
+	iter = container_of(dwork, struct trace_remote_iterator, poll_work);
+	ring_buffer_poll_remote(iter->remote->trace_buffer, iter->cpu);
+	schedule_delayed_work((struct delayed_work *)work,
+			      msecs_to_jiffies(iter->remote->poll_ms));
+}
+
+static struct trace_remote_iterator *trace_remote_iter(struct trace_remote *remote, int cpu)
+{
+	struct trace_remote_iterator *iter;
+	int ret;
+
+	if (remote->nr_readers == ULONG_MAX)
+		return ERR_PTR(-EBUSY);
+
+	ret = trace_remote_load(remote);
+	if (ret)
+		return ERR_PTR(ret);
+
+	/* Test the CPU */
+	ret = ring_buffer_poll_remote(remote->trace_buffer, cpu);
+	if (ret)
+		goto err;
+
+	iter = kzalloc(sizeof(*iter), GFP_KERNEL);
+	if (iter) {
+		remote->nr_readers++;
+
+		iter->remote = remote;
+		iter->cpu = cpu;
+		trace_seq_init(&iter->seq);
+		INIT_DELAYED_WORK(&iter->poll_work, __poll_remote);
+		schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_ms));
+
+		return iter;
+	}
+	ret = -ENOMEM;
+
+err:
+	trace_remote_unload(remote);
+
+	return ERR_PTR(ret);
+}
+
+static bool trace_remote_iter_next(struct trace_remote_iterator *iter)
+{
+	struct trace_buffer *trace_buffer = iter->remote->trace_buffer;
+	int cpu = iter->cpu;
+
+	if (cpu != RING_BUFFER_ALL_CPUS) {
+		if (ring_buffer_empty_cpu(trace_buffer, cpu))
+			return false;
+
+		if (!ring_buffer_peek(trace_buffer, cpu, &iter->ts, &iter->lost_events))
+			return false;
+
+		iter->evt_cpu = cpu;
+		return true;
+	}
+
+	iter->ts = U64_MAX;
+	for_each_possible_cpu(cpu) {
+		unsigned long lost_events;
+		u64 ts;
+
+		if (ring_buffer_empty_cpu(trace_buffer, cpu))
+			continue;
+
+		if (!ring_buffer_peek(trace_buffer, cpu, &ts, &lost_events))
+			continue;
+
+		if (ts >= iter->ts)
+			continue;
+
+		iter->ts = ts;
+		iter->evt_cpu = cpu;
+		iter->lost_events = lost_events;
+	}
+
+	return iter->ts != U64_MAX;
+}
+
+static int trace_remote_iter_print(struct trace_remote_iterator *iter)
+{
+	unsigned long usecs_rem;
+	u64 ts = iter->ts;
+
+	if (iter->lost_events)
+		trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n",
+				 iter->evt_cpu, iter->lost_events);
+
+	do_div(ts, 1000);
+	usecs_rem = do_div(ts, USEC_PER_SEC);
+
+	trace_seq_printf(&iter->seq, "[%03d]\t%5llu.%06lu: ", iter->evt_cpu,
+			 ts, usecs_rem);
+
+	return trace_seq_has_overflowed(&iter->seq) ? -EOVERFLOW : 0;
+}
+
+static int trace_pipe_open(struct inode *inode, struct file *filp)
+{
+	struct trace_remote *remote = inode->i_private;
+	struct trace_remote_iterator *iter;
+	int cpu = RING_BUFFER_ALL_CPUS;
+
+	if (inode->i_cdev)
+		cpu = (long)inode->i_cdev - 1;
+
+	guard(mutex)(&remote->lock);
+	iter = trace_remote_iter(remote, cpu);
+	filp->private_data = iter;
+
+	return IS_ERR(iter) ? PTR_ERR(iter) : 0;
+}
+
+static int trace_pipe_release(struct inode *inode, struct file *filp)
+{
+	struct trace_remote_iterator *iter = filp->private_data;
+	struct trace_remote *remote = iter->remote;
+
+	guard(mutex)(&remote->lock);
+
+	cancel_delayed_work_sync(&iter->poll_work);
+	remote->nr_readers--;
+	trace_remote_unload(remote);
+	kfree(iter);
+
+	return 0;
+}
+
+static ssize_t trace_pipe_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_remote_iterator *iter = filp->private_data;
+	struct trace_buffer *trace_buffer = iter->remote->trace_buffer;
+	int ret;
+
+copy_to_user:
+	ret = trace_seq_to_user(&iter->seq, ubuf, cnt);
+	if (ret != -EBUSY)
+		return ret;
+
+	trace_seq_init(&iter->seq);
+
+	ret = ring_buffer_wait(trace_buffer, iter->cpu, 0, NULL, NULL);
+	if (ret < 0)
+		return ret;
+
+	while (trace_remote_iter_next(iter)) {
+		int prev_len = iter->seq.seq.len;
+
+		if (trace_remote_iter_print(iter)) {
+			iter->seq.seq.len = prev_len;
+			break;
+		}
+
+		ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL);
+	}
+
+	goto copy_to_user;
+}
+
+static const struct file_operations trace_pipe_fops = {
+	.open		= trace_pipe_open,
+	.read		= trace_pipe_read,
+	.release	= trace_pipe_release,
+};
+
+static int trace_remote_init_tracefs(const char *name, struct trace_remote *remote)
+{
+	struct dentry *remote_d, *percpu_d;
+	static struct dentry *root;
+	static DEFINE_MUTEX(lock);
+	bool root_inited = false;
+	int cpu;
+
+	guard(mutex)(&lock);
+
+	if (!root) {
+		root = tracefs_create_dir(TRACEFS_DIR, NULL);
+		if (!root) {
+			pr_err("Failed to create tracefs dir "TRACEFS_DIR"\n");
+			goto err;
+		}
+		root_inited = true;
+	}
+
+	remote_d = tracefs_create_dir(name, root);
+	if (!remote_d) {
+		pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/\n", name);
+		goto err;
+	}
+
+	if (!trace_create_file("tracing_on", TRACEFS_MODE_WRITE, remote_d, remote,
+			       &tracing_on_fops) ||
+	    !trace_create_file("buffer_size_kb", TRACEFS_MODE_WRITE, remote_d, remote,
+			       &buffer_size_kb_fops) ||
+	    !trace_create_file("trace_pipe", TRACEFS_MODE_READ, remote_d, remote,
+			       &trace_pipe_fops))
+		goto err;
+
+	percpu_d = tracefs_create_dir("per_cpu", remote_d);
+	if (!percpu_d) {
+		pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/per_cpu/\n", name);
+		goto err;
+	}
+
+	for_each_possible_cpu(cpu) {
+		struct dentry *cpu_d;
+		char cpu_name[16];
+
+		snprintf(cpu_name, sizeof(cpu_name), "cpu%d", cpu);
+		cpu_d = tracefs_create_dir(cpu_name, percpu_d);
+		if (!cpu_d) {
+			pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/percpu/cpu%d\n",
+			       name, cpu);
+			goto err;
+		}
+
+		if (!trace_create_cpu_file("trace_pipe", TRACEFS_MODE_READ, cpu_d, remote, cpu,
+					   &trace_pipe_fops))
+			goto err;
+	}
+
+	return 0;
+
+err:
+	if (root_inited) {
+		tracefs_remove(root);
+		root = NULL;
+	} else {
+		tracefs_remove(remote_d);
+	}
+
+	return -ENOMEM;
+}
+
+int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv)
+{
+	struct trace_remote *remote;
+
+	remote = kzalloc(sizeof(*remote), GFP_KERNEL);
+	if (!remote)
+		return -ENOMEM;
+
+	remote->cbs = cbs;
+	remote->priv = priv;
+	remote->trace_buffer_size = 7 << 10;
+	remote->poll_ms = 100;
+	mutex_init(&remote->lock);
+
+	if (trace_remote_init_tracefs(name, remote)) {
+		kfree(remote);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+void trace_remote_free_buffer(struct trace_buffer_desc *desc)
+{
+	struct ring_buffer_desc *rb_desc;
+	int cpu;
+
+	for_each_ring_buffer_desc(rb_desc, cpu, desc) {
+		unsigned int id;
+
+		free_page(rb_desc->meta_va);
+
+		for (id = 0; id < rb_desc->nr_page_va; id++)
+			free_page(rb_desc->page_va[id]);
+	}
+}
+
+int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t size,
+			      const struct cpumask *cpumask)
+{
+	int nr_pages = (PAGE_ALIGN(size) / PAGE_SIZE) + 1;
+	struct ring_buffer_desc *rb_desc;
+	int cpu;
+
+	desc->nr_cpus = 0;
+	desc->struct_len = offsetof(struct trace_buffer_desc, __data);
+
+	rb_desc = (struct ring_buffer_desc *)&desc->__data[0];
+
+	for_each_cpu(cpu, cpumask) {
+		unsigned int id;
+
+		rb_desc->cpu = cpu;
+		rb_desc->nr_page_va = 0;
+		rb_desc->meta_va = (unsigned long)__get_free_page(GFP_KERNEL);
+		if (!rb_desc->meta_va)
+			goto err;
+
+		for (id = 0; id < nr_pages; id++) {
+			rb_desc->page_va[id] = (unsigned long)__get_free_page(GFP_KERNEL);
+			if (!rb_desc->page_va[id])
+				goto err;
+
+			rb_desc->nr_page_va++;
+		}
+		desc->nr_cpus++;
+		desc->struct_len += offsetof(struct ring_buffer_desc, page_va);
+		desc->struct_len += sizeof(rb_desc->page_va[0]) * rb_desc->nr_page_va;
+		rb_desc = __next_ring_buffer_desc(rb_desc);
+	}
+
+	return 0;
+
+err:
+	trace_remote_free_buffer(desc);
+	return -ENOMEM;
+}
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 03/24] tracing: Add reset to trace remotes

[Vincent Donnefort]

For standard trace instance, "trace" files allow to do non-consuming
read of the ring-buffers. This is however not applicable to ring-buffer
remotes due to the lack of support in the meta-page. Nonetheless this
file is still useful to reset a ring-buffer so let's add a write-only
version.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
index de043a6f2fe0..1aa99da3c96a 100644
--- a/include/linux/trace_remote.h
+++ b/include/linux/trace_remote.h
@@ -11,6 +11,7 @@ struct trace_remote_callbacks {
 	void	(*unload_trace_buffer)(struct trace_buffer_desc *desc, void *priv);
 	int	(*enable_tracing)(bool enable, void *priv);
 	int	(*swap_reader_page)(unsigned int cpu, void *priv);
+	int	(*reset)(unsigned int cpu, void *priv);
 };
 
 int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv);
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 462c2d085a08..2221705f65f4 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -70,6 +70,7 @@ static int trace_remote_load(struct trace_remote *remote)
 	rb_remote->desc = remote->trace_buffer_desc;
 	rb_remote->swap_reader_page = remote->cbs->swap_reader_page;
 	rb_remote->priv = remote->priv;
+	rb_remote->reset = remote->cbs->reset;
 	remote->trace_buffer = ring_buffer_remote(rb_remote);
 	if (!remote->trace_buffer) {
 		remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv);
@@ -135,6 +136,19 @@ static int trace_remote_stop(struct trace_remote *remote)
 	return 0;
 }
 
+static void trace_remote_reset(struct trace_remote *remote, int cpu)
+{
+	lockdep_assert_held(&remote->lock);
+
+	if (!trace_remote_loaded(remote))
+		return;
+
+	if (cpu == RING_BUFFER_ALL_CPUS)
+		ring_buffer_reset(remote->trace_buffer);
+	else
+		ring_buffer_reset_cpu(remote->trace_buffer, cpu);
+}
+
 static ssize_t
 tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
 {
@@ -369,6 +383,26 @@ static const struct file_operations trace_pipe_fops = {
 	.release	= trace_pipe_release,
 };
 
+static ssize_t trace_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct inode *inode = file_inode(filp);
+	struct trace_remote *remote = inode->i_private;
+	int cpu = RING_BUFFER_ALL_CPUS;
+
+	if (inode->i_cdev)
+		cpu = (long)inode->i_cdev - 1;
+
+	guard(mutex)(&remote->lock);
+
+	trace_remote_reset(remote, cpu);
+
+	return cnt;
+}
+
+static const struct file_operations trace_fops = {
+	.write		= trace_write,
+};
+
 static int trace_remote_init_tracefs(const char *name, struct trace_remote *remote)
 {
 	struct dentry *remote_d, *percpu_d;
@@ -399,7 +433,9 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 	    !trace_create_file("buffer_size_kb", TRACEFS_MODE_WRITE, remote_d, remote,
 			       &buffer_size_kb_fops) ||
 	    !trace_create_file("trace_pipe", TRACEFS_MODE_READ, remote_d, remote,
-			       &trace_pipe_fops))
+			       &trace_pipe_fops) ||
+	    !trace_create_file("trace", 0200, remote_d, remote,
+			       &trace_fops))
 		goto err;
 
 	percpu_d = tracefs_create_dir("per_cpu", remote_d);
@@ -421,7 +457,9 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 		}
 
 		if (!trace_create_cpu_file("trace_pipe", TRACEFS_MODE_READ, cpu_d, remote, cpu,
-					   &trace_pipe_fops))
+					   &trace_pipe_fops) ||
+		    !trace_create_cpu_file("trace", 0200, cpu_d, remote, cpu,
+					   &trace_fops))
 			goto err;
 	}
 
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 04/24] tracing: Add init callback to trace remotes

[Vincent Donnefort]

Add a .init call back so the trace remote callers can add entries to the
tracefs directory.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
index 1aa99da3c96a..82d26d97a536 100644
--- a/include/linux/trace_remote.h
+++ b/include/linux/trace_remote.h
@@ -3,9 +3,11 @@
 #ifndef _LINUX_TRACE_REMOTE_H
 #define _LINUX_TRACE_REMOTE_H
 
+#include <linux/dcache.h>
 #include <linux/ring_buffer.h>
 
 struct trace_remote_callbacks {
+	int	(*init)(struct dentry *d, void *priv);
 	struct trace_buffer_desc *
 		(*load_trace_buffer)(unsigned long size, void *priv);
 	void	(*unload_trace_buffer)(struct trace_buffer_desc *desc, void *priv);
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 2221705f65f4..6f4b921f6955 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -479,6 +479,7 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv)
 {
 	struct trace_remote *remote;
+	int ret;
 
 	remote = kzalloc(sizeof(*remote), GFP_KERNEL);
 	if (!remote)
@@ -495,7 +496,11 @@ int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs,
 		return -ENOMEM;
 	}
 
-	return 0;
+	ret = cbs->init ? cbs->init(remote->dentry, priv) : 0;
+	if (ret)
+		pr_err("Init failed for trace remote '%s' (%d)\n", name, ret);
+
+	return ret;
 }
 
 void trace_remote_free_buffer(struct trace_buffer_desc *desc)
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 05/24] tracing: Add events to trace remotes

[Vincent Donnefort]

An event is predefined point in the writer code that allows to log
data. Following the same scheme as kernel events, add remote events,
described to user-space within the events/ tracefs directory found in
the corresponding trace remote.

Remote events are expected to be described during the trace remote
registration.

Add also a .enable_event callback for trace_remote to toggle the event
logging, if supported.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
index 82d26d97a536..4cf8efa83578 100644
--- a/include/linux/trace_remote.h
+++ b/include/linux/trace_remote.h
@@ -5,6 +5,7 @@
 
 #include <linux/dcache.h>
 #include <linux/ring_buffer.h>
+#include <linux/trace_remote_event.h>
 
 struct trace_remote_callbacks {
 	int	(*init)(struct dentry *d, void *priv);
@@ -14,9 +15,11 @@ struct trace_remote_callbacks {
 	int	(*enable_tracing)(bool enable, void *priv);
 	int	(*swap_reader_page)(unsigned int cpu, void *priv);
 	int	(*reset)(unsigned int cpu, void *priv);
+	int	(*enable_event)(unsigned short id, bool enable, void *priv);
 };
 
-int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv);
+int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv,
+			  struct remote_event *events, size_t nr_events);
 int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t size,
 			      const struct cpumask *cpumask);
 void trace_remote_free_buffer(struct trace_buffer_desc *desc);
diff --git a/include/linux/trace_remote_event.h b/include/linux/trace_remote_event.h
new file mode 100644
index 000000000000..621c5dff0664
--- /dev/null
+++ b/include/linux/trace_remote_event.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_TRACE_REMOTE_EVENTS_H
+#define _LINUX_TRACE_REMOTE_EVENTS_H
+
+struct trace_remote;
+struct trace_event_fields;
+
+struct remote_event_hdr {
+	unsigned short	id;
+};
+
+#define REMOTE_EVENT_NAME_MAX 29
+struct remote_event {
+	char				name[REMOTE_EVENT_NAME_MAX];
+	unsigned short			id;
+	bool				enabled;
+	struct trace_remote		*remote;
+	struct trace_event_fields	*fields;
+	char				*print_fmt;
+	void				(*print)(void *evt, struct trace_seq *seq);
+};
+#endif
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 6f4b921f6955..00ef80da043b 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -24,6 +24,7 @@ struct trace_remote_iterator {
 	struct delayed_work		poll_work;
 	unsigned long			lost_events;
 	u64				ts;
+	struct remote_event_hdr		*evt;
 	int				cpu;
 	int				evt_cpu;
 };
@@ -33,6 +34,10 @@ struct trace_remote {
 	void				*priv;
 	struct trace_buffer		*trace_buffer;
 	struct trace_buffer_desc	*trace_buffer_desc;
+	struct dentry			*dentry;
+	struct eventfs_inode		*eventfs;
+	struct remote_event		*events;
+	unsigned long			nr_events;
 	unsigned long			trace_buffer_size;
 	struct ring_buffer_remote	rb_remote;
 	struct mutex			lock;
@@ -152,7 +157,8 @@ static void trace_remote_reset(struct trace_remote *remote, int cpu)
 static ssize_t
 tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
 {
-	struct trace_remote *remote = filp->private_data;
+	struct seq_file *seq = filp->private_data;
+	struct trace_remote *remote = seq->private;
 	unsigned long val;
 	int ret;
 
@@ -181,7 +187,8 @@ DEFINE_SHOW_STORE_ATTRIBUTE(tracing_on);
 static ssize_t buffer_size_kb_write(struct file *filp, const char __user *ubuf, size_t cnt,
 				    loff_t *ppos)
 {
-	struct trace_remote *remote = filp->private_data;
+	struct seq_file *seq = filp->private_data;
+	struct trace_remote *remote = seq->private;
 	unsigned long val;
 	int ret;
 
@@ -262,16 +269,19 @@ static struct trace_remote_iterator *trace_remote_iter(struct trace_remote *remo
 static bool trace_remote_iter_next(struct trace_remote_iterator *iter)
 {
 	struct trace_buffer *trace_buffer = iter->remote->trace_buffer;
+	struct ring_buffer_event *rb_evt;
 	int cpu = iter->cpu;
 
 	if (cpu != RING_BUFFER_ALL_CPUS) {
 		if (ring_buffer_empty_cpu(trace_buffer, cpu))
 			return false;
 
-		if (!ring_buffer_peek(trace_buffer, cpu, &iter->ts, &iter->lost_events))
+		rb_evt = ring_buffer_peek(trace_buffer, cpu, &iter->ts, &iter->lost_events);
+		if (!rb_evt)
 			return false;
 
 		iter->evt_cpu = cpu;
+		iter->evt = (struct remote_event_hdr *)&rb_evt->array[1];
 		return true;
 	}
 
@@ -283,7 +293,8 @@ static bool trace_remote_iter_next(struct trace_remote_iterator *iter)
 		if (ring_buffer_empty_cpu(trace_buffer, cpu))
 			continue;
 
-		if (!ring_buffer_peek(trace_buffer, cpu, &ts, &lost_events))
+		rb_evt = ring_buffer_peek(trace_buffer, cpu, &ts, &lost_events);
+		if (!rb_evt)
 			continue;
 
 		if (ts >= iter->ts)
@@ -291,14 +302,18 @@ static bool trace_remote_iter_next(struct trace_remote_iterator *iter)
 
 		iter->ts = ts;
 		iter->evt_cpu = cpu;
+		iter->evt = (struct remote_event_hdr *)&rb_evt->array[1];
 		iter->lost_events = lost_events;
 	}
 
 	return iter->ts != U64_MAX;
 }
 
+static struct remote_event *trace_remote_find_event(struct trace_remote *remote, unsigned short id);
+
 static int trace_remote_iter_print(struct trace_remote_iterator *iter)
 {
+	struct remote_event *evt;
 	unsigned long usecs_rem;
 	u64 ts = iter->ts;
 
@@ -312,6 +327,12 @@ static int trace_remote_iter_print(struct trace_remote_iterator *iter)
 	trace_seq_printf(&iter->seq, "[%03d]\t%5llu.%06lu: ", iter->evt_cpu,
 			 ts, usecs_rem);
 
+	evt = trace_remote_find_event(iter->remote, iter->evt->id);
+	if (!evt)
+		trace_seq_printf(&iter->seq, "UNKNOWN id=%d\n", iter->evt->id);
+	else
+		evt->print(iter->evt, &iter->seq);
+
 	return trace_seq_has_overflowed(&iter->seq) ? -EOVERFLOW : 0;
 }
 
@@ -463,6 +484,8 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 			goto err;
 	}
 
+	remote->dentry = remote_d;
+
 	return 0;
 
 err:
@@ -476,7 +499,11 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 	return -ENOMEM;
 }
 
-int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv)
+static int trace_remote_register_events(const char *remote_name, struct trace_remote *remote,
+					struct remote_event *events, size_t nr_events);
+
+int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv,
+			  struct remote_event *events, size_t nr_events)
 {
 	struct trace_remote *remote;
 	int ret;
@@ -496,6 +523,13 @@ int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs,
 		return -ENOMEM;
 	}
 
+	ret = trace_remote_register_events(name, remote, events, nr_events);
+	if (ret) {
+		pr_err("Failed to register events for trace remote '%s' (%d)\n",
+		       name, ret);
+		return ret;
+	}
+
 	ret = cbs->init ? cbs->init(remote->dentry, priv) : 0;
 	if (ret)
 		pr_err("Init failed for trace remote '%s' (%d)\n", name, ret);
@@ -558,3 +592,220 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t size,
 	trace_remote_free_buffer(desc);
 	return -ENOMEM;
 }
+
+static int
+trace_remote_enable_event(struct trace_remote *remote, struct remote_event *evt, bool enable)
+{
+	int ret;
+
+	lockdep_assert_held(&remote->lock);
+
+	if (evt->enabled == enable)
+		return 0;
+
+	ret = remote->cbs->enable_event(evt->id, enable, remote->priv);
+	if (ret)
+		return ret;
+
+	evt->enabled = enable;
+
+	return 0;
+}
+
+static int remote_event_enable_show(struct seq_file *s, void *unused)
+{
+	struct remote_event *evt = s->private;
+
+	seq_printf(s, "%d\n", evt->enabled);
+
+	return 0;
+}
+
+static ssize_t remote_event_enable_write(struct file *filp, const char __user *ubuf,
+					 size_t count, loff_t *ppos)
+{
+	struct seq_file *seq = filp->private_data;
+	struct remote_event *evt = seq->private;
+	struct trace_remote *remote = evt->remote;
+	u8 enable;
+	int ret;
+
+	ret = kstrtou8_from_user(ubuf, count, 10, &enable);
+	if (ret)
+		return ret;
+
+	guard(mutex)(&remote->lock);
+
+	ret = trace_remote_enable_event(remote, evt, enable);
+	if (ret)
+		return ret;
+
+	return count;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(remote_event_enable);
+
+static int remote_event_id_show(struct seq_file *s, void *unused)
+{
+	struct remote_event *evt = s->private;
+
+	seq_printf(s, "%d\n", evt->id);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(remote_event_id);
+
+static int remote_event_format_show(struct seq_file *s, void *unused)
+{
+	size_t offset = sizeof(struct remote_event_hdr);
+	struct remote_event *evt = s->private;
+	struct trace_event_fields *field;
+
+	seq_printf(s, "name: %s\n", evt->name);
+	seq_printf(s, "ID: %d\n", evt->id);
+	seq_puts(s,
+		 "format:\n\tfield:unsigned short common_type;\toffset:0;\tsize:2;\tsigned:0;\n\n");
+
+	field = &evt->fields[0];
+	while (field->name) {
+		seq_printf(s, "\tfield:%s %s;\toffset:%lu;\tsize:%u;\tsigned:%d;\n",
+			   field->type, field->name, offset, field->size,
+			   !field->is_signed);
+		offset += field->size;
+		field++;
+	}
+
+	if (field != &evt->fields[0])
+		seq_puts(s, "\n");
+
+	seq_printf(s, "print fmt: %s\n", evt->print_fmt);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(remote_event_format);
+
+static int remote_event_callback(const char *name, umode_t *mode, void **data,
+				 const struct file_operations **fops)
+{
+	if (!strcmp(name, "enable")) {
+		*mode = TRACEFS_MODE_WRITE;
+		*fops = &remote_event_enable_fops;
+		return 1;
+	}
+
+	if (!strcmp(name, "id")) {
+		*mode = TRACEFS_MODE_READ;
+		*fops = &remote_event_id_fops;
+		return 1;
+	}
+
+	if (!strcmp(name, "format")) {
+		*mode = TRACEFS_MODE_READ;
+		*fops = &remote_event_id_fops;
+		return 1;
+	}
+
+	return 0;
+}
+
+static int trace_remote_init_eventfs(const char *remote_name, struct trace_remote *remote,
+				     struct remote_event *evt)
+{
+	struct eventfs_inode *eventfs = remote->eventfs;
+	static struct eventfs_entry entries[] = {
+		{
+			.name		= "enable",
+			.callback	= remote_event_callback,
+		}, {
+			.name		= "id",
+			.callback	= remote_event_callback,
+		}, {
+			.name		= "format",
+			.callback	= remote_event_callback,
+		}
+	};
+	bool eventfs_create = false;
+
+	if (!eventfs) {
+		eventfs = eventfs_create_events_dir("events", remote->dentry, NULL, 0, NULL);
+		if (IS_ERR(eventfs))
+			return PTR_ERR(eventfs);
+
+		/*
+		 * Create similar hierarchy as local events even if a single system is supported at
+		 * the moment
+		 */
+		eventfs = eventfs_create_dir(remote_name, eventfs, NULL, 0, NULL);
+		if (IS_ERR(eventfs))
+			return PTR_ERR(eventfs);
+
+		remote->eventfs = eventfs;
+		eventfs_create = true;
+	}
+
+	eventfs = eventfs_create_dir(evt->name, eventfs, entries, ARRAY_SIZE(entries), evt);
+	if (IS_ERR(eventfs)) {
+		if (eventfs_create) {
+			eventfs_remove_events_dir(remote->eventfs);
+			remote->eventfs = NULL;
+		}
+		return PTR_ERR(eventfs);
+	}
+
+	return 0;
+}
+
+static int trace_remote_attach_events(struct trace_remote *remote, struct remote_event *events,
+				      size_t nr_events)
+{
+	int i;
+
+	for (i = 0; i < nr_events; i++) {
+		struct remote_event *evt = &events[i];
+
+		if (evt->remote)
+			return -EEXIST;
+
+		evt->remote = remote;
+
+		/* We need events to be sorted for efficient lookup */
+		if (i && evt->id <= events[i - 1].id)
+			return -EINVAL;
+	}
+
+	remote->events = events;
+	remote->nr_events = nr_events;
+
+	return 0;
+}
+
+static int trace_remote_register_events(const char *remote_name, struct trace_remote *remote,
+					struct remote_event *events, size_t nr_events)
+{
+	int i, ret;
+
+	ret = trace_remote_attach_events(remote, events, nr_events);
+	if (ret)
+		return ret;
+
+	for (i = 0; i < nr_events; i++) {
+		struct remote_event *evt = &events[i];
+
+		ret = trace_remote_init_eventfs(remote_name, remote, evt);
+		if (ret)
+			pr_warn("Failed to init eventfs for event '%s' (%d)",
+				evt->name, ret);
+	}
+
+	return 0;
+}
+
+static int __cmp_events(const void *id, const void *evt)
+{
+	return (long)id - ((struct remote_event *)evt)->id;
+}
+
+static struct remote_event *trace_remote_find_event(struct trace_remote *remote, unsigned short id)
+{
+	return bsearch((const void *)(unsigned long)id, remote->events, remote->nr_events,
+		       sizeof(*remote->events), __cmp_events);
+}
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 06/24] tracing: Add events/ root files to trace remotes

[Vincent Donnefort]

Just like for the kernel events directory, add 'enable', 'header_page'
and 'header_event' at the root of the trace remote events/ directory.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a96a0b231fee..cff1e700d4b7 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -604,7 +604,8 @@ int ring_buffer_print_page_header(struct trace_buffer *buffer, struct trace_seq
 	trace_seq_printf(s, "\tfield: char data;\t"
 			 "offset:%u;\tsize:%u;\tsigned:%u;\n",
 			 (unsigned int)offsetof(typeof(field), data),
-			 (unsigned int)buffer->subbuf_size,
+			 (unsigned int)(buffer ? buffer->subbuf_size :
+						 PAGE_SIZE - BUF_PAGE_HDR_SIZE),
 			 (unsigned int)is_signed_type(char));
 
 	return !trace_seq_has_overflowed(s);
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 00ef80da043b..5c9f2b07941f 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -707,10 +707,118 @@ static int remote_event_callback(const char *name, umode_t *mode, void **data,
 	return 0;
 }
 
+static ssize_t remote_events_dir_enable_write(struct file *filp, const char __user *ubuf,
+					      size_t count, loff_t *ppos)
+{
+	struct trace_remote *remote = file_inode(filp)->i_private;
+	u8 enable;
+	int i, ret;
+
+	ret = kstrtou8_from_user(ubuf, count, 10, &enable);
+	if (ret)
+		return ret;
+
+	guard(mutex)(&remote->lock);
+
+	for (i = 0; i < remote->nr_events; i++) {
+		struct remote_event *evt = &remote->events[i];
+
+		trace_remote_enable_event(remote, evt, enable);
+	}
+
+	return count;
+}
+
+static const struct file_operations remote_events_dir_enable_fops = {
+	.write = remote_events_dir_enable_write,
+};
+
+static ssize_t
+remote_events_dir_header_page_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_seq *s;
+	int ret;
+
+	s = kmalloc(sizeof(*s), GFP_KERNEL);
+	if (!s)
+		return -ENOMEM;
+
+	trace_seq_init(s);
+
+	ring_buffer_print_page_header(NULL, s);
+	ret = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, trace_seq_used(s));
+	kfree(s);
+
+	return ret;
+}
+
+static const struct file_operations remote_events_dir_header_page_fops = {
+	.read = remote_events_dir_header_page_read,
+};
+
+static ssize_t
+remote_events_dir_header_event_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_seq *s;
+	int ret;
+
+	s = kmalloc(sizeof(*s), GFP_KERNEL);
+	if (!s)
+		return -ENOMEM;
+
+	trace_seq_init(s);
+
+	ring_buffer_print_entry_header(s);
+	ret = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, trace_seq_used(s));
+	kfree(s);
+
+	return ret;
+}
+
+static const struct file_operations remote_events_dir_header_event_fops = {
+	.read = remote_events_dir_header_event_read,
+};
+
+static int remote_events_dir_callback(const char *name, umode_t *mode, void **data,
+				      const struct file_operations **fops)
+{
+	if (!strcmp(name, "enable")) {
+		*mode = 0200;
+		*fops = &remote_events_dir_enable_fops;
+		return 1;
+	}
+
+	if (!strcmp(name, "header_page")) {
+		*mode = TRACEFS_MODE_READ;
+		*fops = &remote_events_dir_header_page_fops;
+		return 1;
+	}
+
+	if (!strcmp(name, "header_event")) {
+		*mode = TRACEFS_MODE_READ;
+		*fops = &remote_events_dir_header_event_fops;
+		return 1;
+	}
+
+	return 0;
+}
+
 static int trace_remote_init_eventfs(const char *remote_name, struct trace_remote *remote,
 				     struct remote_event *evt)
 {
 	struct eventfs_inode *eventfs = remote->eventfs;
+	static struct eventfs_entry dir_entries[] = {
+		{
+			.name		= "enable",
+			.callback	= remote_events_dir_callback,
+		}, {
+			.name		= "header_page",
+			.callback	= remote_events_dir_callback,
+		}, {
+			.name		= "header_event",
+			.callback	= remote_events_dir_callback,
+		}
+	};
 	static struct eventfs_entry entries[] = {
 		{
 			.name		= "enable",
@@ -726,7 +834,8 @@ static int trace_remote_init_eventfs(const char *remote_name, struct trace_remot
 	bool eventfs_create = false;
 
 	if (!eventfs) {
-		eventfs = eventfs_create_events_dir("events", remote->dentry, NULL, 0, NULL);
+		eventfs = eventfs_create_events_dir("events", remote->dentry, dir_entries,
+						    ARRAY_SIZE(dir_entries), remote);
 		if (IS_ERR(eventfs))
 			return PTR_ERR(eventfs);
 
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 07/24] tracing: Add helpers to create trace remote events

[Vincent Donnefort]

Declaring remote events can be cumbersome let's add a set of macros to
simplify developers life. The declaration of a remote event is very
similar to kernel's events:

 REMOTE_EVENT(name, id,
     RE_STRUCT(
        re_field(u64 foo)
     ),
     RE_PRINTK("foo=%llu", __entry->foo)
 )

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/trace_remote_event.h b/include/linux/trace_remote_event.h
index 621c5dff0664..d00e85d2a633 100644
--- a/include/linux/trace_remote_event.h
+++ b/include/linux/trace_remote_event.h
@@ -5,6 +5,7 @@
 
 struct trace_remote;
 struct trace_event_fields;
+struct trace_seq;
 
 struct remote_event_hdr {
 	unsigned short	id;
@@ -20,4 +21,13 @@ struct remote_event {
 	char				*print_fmt;
 	void				(*print)(void *evt, struct trace_seq *seq);
 };
+
+#define RE_STRUCT(__args...) __args
+#define re_field(__type, __field) __type __field;
+
+#define REMOTE_EVENT_FORMAT(__name, __struct)	\
+	struct remote_event_format_##__name {	\
+		struct remote_event_hdr hdr;	\
+		__struct			\
+	}
 #endif
diff --git a/include/trace/define_remote_events.h b/include/trace/define_remote_events.h
new file mode 100644
index 000000000000..03c9f5515c5a
--- /dev/null
+++ b/include/trace/define_remote_events.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/trace_events.h>
+#include <linux/trace_remote_event.h>
+#include <linux/trace_seq.h>
+#include <linux/stringify.h>
+
+#define REMOTE_EVENT_INCLUDE(__file) __stringify(../../__file)
+
+#ifdef REMOTE_EVENT_SECTION
+# define __REMOTE_EVENT_SECTION(__name) __used __section(REMOTE_EVENT_SECTION"."#__name)
+#else
+# define __REMOTE_EVENT_SECTION(__name)
+#endif
+
+#define __REMOTE_PRINTK_COUNT_ARGS(_0, _1, _2, _n, __args...) _n
+#define REMOTE_PRINTK_COUNT_ARGS(__args...) __REMOTE_PRINTK_COUNT_ARGS(, ##__args, 2, 1, 0)
+
+#define __remote_printk0()								\
+	trace_seq_putc(seq, '\n')
+
+#define __remote_printk1(__fmt)								\
+	trace_seq_puts(seq, " " __fmt "\n")						\
+
+#define __remote_printk2(__fmt, __args...)						\
+do {											\
+	trace_seq_putc(seq, ' ');							\
+	trace_seq_printf(seq, __fmt, __args);						\
+	trace_seq_putc(seq, '\n');							\
+} while (0)
+
+/* Apply the appropriate trace_seq sequence according to the number of arguments */
+#define remote_printk(__args...)							\
+	CONCATENATE(__remote_printk, REMOTE_PRINTK_COUNT_ARGS(__args))(__args)
+
+#define RE_PRINTK(__args...) __args
+
+#define REMOTE_EVENT(__name, __id, __struct, __printk)					\
+	REMOTE_EVENT_FORMAT(__name, __struct);						\
+	static void remote_event_print_##__name(void *evt, struct trace_seq *seq)	\
+	{										\
+		struct remote_event_format_##__name __maybe_unused *__entry = evt;	\
+		trace_seq_puts(seq, #__name);						\
+		remote_printk(__printk);						\
+	}
+#include REMOTE_EVENT_INCLUDE(REMOTE_EVENT_INCLUDE_FILE)
+
+#undef REMOTE_EVENT
+#undef RE_PRINTK
+#undef re_field
+#define re_field(__type, __field)							\
+	{										\
+		.type = #__type, .name = #__field,					\
+		.size = sizeof(__type), .align = __alignof__(__type),			\
+		.is_signed = is_signed_type(__type),					\
+	},
+#define __entry REC
+#define RE_PRINTK(__fmt, __args...) "\"" __fmt "\", " __stringify(__args)
+#define REMOTE_EVENT(__name, __id, __struct, __printk)					\
+	static struct trace_event_fields remote_event_fields_##__name[] = {		\
+		__struct								\
+		{}									\
+	};										\
+	static char remote_event_print_fmt_##__name[] = __printk;			\
+	static struct remote_event __REMOTE_EVENT_SECTION(__name)			\
+	remote_event_##__name = {							\
+		.name		= #__name,						\
+		.id		= __id,							\
+		.fields		= remote_event_fields_##__name,				\
+		.print_fmt	= remote_event_print_fmt_##__name,			\
+		.print		= remote_event_print_##__name,				\
+	}
+#include REMOTE_EVENT_INCLUDE(REMOTE_EVENT_INCLUDE_FILE)
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 08/24] ring-buffer: Expose buffer_data_page material

[Vincent Donnefort]

In preparation for allowing the write of ring-buffer compliant pages
outside of ring_buffer.c, move buffer_data_page and timestamps
encoding functions into the publicly available ring_buffer.h.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index c0c7f8a0dcb3..c26fba4a643c 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -3,8 +3,10 @@
 #define _LINUX_RING_BUFFER_H
 
 #include <linux/mm.h>
-#include <linux/seq_file.h>
 #include <linux/poll.h>
+#include <linux/seq_file.h>
+
+#include <asm/local.h>
 
 #include <uapi/linux/trace_mmap.h>
 
@@ -61,11 +63,46 @@ enum ring_buffer_type {
 	RINGBUF_TYPE_TIME_STAMP,
 };
 
+#define TS_SHIFT        27
+#define TS_MASK         ((1ULL << TS_SHIFT) - 1)
+#define TS_DELTA_TEST   (~TS_MASK)
+
+/*
+ * We need to fit the time_stamp delta into 27 bits.
+ */
+static inline bool test_time_stamp(u64 delta)
+{
+	return !!(delta & TS_DELTA_TEST);
+}
+
 unsigned ring_buffer_event_length(struct ring_buffer_event *event);
 void *ring_buffer_event_data(struct ring_buffer_event *event);
 u64 ring_buffer_event_time_stamp(struct trace_buffer *buffer,
 				 struct ring_buffer_event *event);
 
+#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
+
+#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
+#define RB_ALIGNMENT		4U
+#define RB_MAX_SMALL_DATA	(RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
+#define RB_EVNT_MIN_SIZE	8U	/* two 32bit words */
+
+#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
+# define RB_FORCE_8BYTE_ALIGNMENT	0
+# define RB_ARCH_ALIGNMENT		RB_ALIGNMENT
+#else
+# define RB_FORCE_8BYTE_ALIGNMENT	1
+# define RB_ARCH_ALIGNMENT		8U
+#endif
+
+#define RB_ALIGN_DATA		__aligned(RB_ARCH_ALIGNMENT)
+
+struct buffer_data_page {
+	u64		 time_stamp;	/* page time stamp */
+	local_t		 commit;	/* write committed index */
+	unsigned char	 data[] RB_ALIGN_DATA;	/* data of buffer page */
+};
+
 /*
  * ring_buffer_discard_commit will remove an event that has not
  *   been committed yet. If this is used, then ring_buffer_unlock_commit
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index cff1e700d4b7..e99e8d4ab615 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -156,23 +156,6 @@ int ring_buffer_print_entry_header(struct trace_seq *s)
 /* Used for individual buffers (after the counter) */
 #define RB_BUFFER_OFF		(1 << 20)
 
-#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
-
-#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
-#define RB_ALIGNMENT		4U
-#define RB_MAX_SMALL_DATA	(RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
-#define RB_EVNT_MIN_SIZE	8U	/* two 32bit words */
-
-#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
-# define RB_FORCE_8BYTE_ALIGNMENT	0
-# define RB_ARCH_ALIGNMENT		RB_ALIGNMENT
-#else
-# define RB_FORCE_8BYTE_ALIGNMENT	1
-# define RB_ARCH_ALIGNMENT		8U
-#endif
-
-#define RB_ALIGN_DATA		__aligned(RB_ARCH_ALIGNMENT)
-
 /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
 #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
 
@@ -315,10 +298,6 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
 #define for_each_online_buffer_cpu(buffer, cpu)		\
 	for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
 
-#define TS_SHIFT	27
-#define TS_MASK		((1ULL << TS_SHIFT) - 1)
-#define TS_DELTA_TEST	(~TS_MASK)
-
 static u64 rb_event_time_stamp(struct ring_buffer_event *event)
 {
 	u64 ts;
@@ -337,12 +316,6 @@ static u64 rb_event_time_stamp(struct ring_buffer_event *event)
 
 #define RB_MISSED_MASK		(3 << 30)
 
-struct buffer_data_page {
-	u64		 time_stamp;	/* page time stamp */
-	local_t		 commit;	/* write committed index */
-	unsigned char	 data[] RB_ALIGN_DATA;	/* data of buffer page */
-};
-
 struct buffer_data_read_page {
 	unsigned		order;	/* order of the page */
 	struct buffer_data_page	*data;	/* actual data, stored in this page */
@@ -401,14 +374,6 @@ static void free_buffer_page(struct buffer_page *bpage)
 	kfree(bpage);
 }
 
-/*
- * We need to fit the time_stamp delta into 27 bits.
- */
-static inline bool test_time_stamp(u64 delta)
-{
-	return !!(delta & TS_DELTA_TEST);
-}
-
 struct rb_irq_work {
 	struct irq_work			work;
 	wait_queue_head_t		waiters;
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 09/24] tracing: Introduce simple_ring_buffer

[Vincent Donnefort]

Add a simple implementation of the kernel ring-buffer. This intends to
be used later by ring-buffer remotes such as the pKVM hypervisor, hence
the need for a cut down version (write only) without any dependency.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/simple_ring_buffer.h b/include/linux/simple_ring_buffer.h
new file mode 100644
index 000000000000..6cf8486d46e2
--- /dev/null
+++ b/include/linux/simple_ring_buffer.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_SIMPLE_RING_BUFFER_H
+#define _LINUX_SIMPLE_RING_BUFFER_H
+
+#include <linux/list.h>
+#include <linux/ring_buffer.h>
+#include <linux/types.h>
+
+/*
+ * Ideally those struct would stay private but the caller needs to know how big they are to allocate
+ * the memory for simple_ring_buffer_init().
+ */
+struct simple_buffer_page {
+	struct list_head	list;
+	struct buffer_data_page	*page;
+	u64			entries;
+	u32			write;
+	u32			id;
+};
+
+struct simple_rb_per_cpu {
+	struct simple_buffer_page	*tail_page;
+	struct simple_buffer_page	*reader_page;
+	struct simple_buffer_page	*head_page;
+	struct simple_buffer_page	*bpages;
+	struct trace_buffer_meta	*meta;
+	u32				nr_pages;
+
+#define SIMPLE_RB_UNAVAILABLE	0
+#define SIMPLE_RB_READY		1
+#define SIMPLE_RB_WRITING	2
+	u32				status;
+
+	u64				last_overrun;
+	u64				write_stamp;
+
+	struct simple_rb_cbs		*cbs;
+};
+
+void *simple_ring_buffer_reserve(struct simple_rb_per_cpu *cpu_buffer, unsigned long length,
+				 u64 timestamp);
+void simple_ring_buffer_commit(struct simple_rb_per_cpu *cpu_buffer);
+void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer);
+int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_buffer_page *bpages,
+			    const struct ring_buffer_desc *desc);
+int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool enable);
+int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer);
+int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer);
+#endif
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 2fcc86c7fe7e..407cb05cc8a0 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -1218,4 +1218,7 @@ source "kernel/trace/rv/Kconfig"
 config TRACE_REMOTE
 	bool
 
+config SIMPLE_RING_BUFFER
+	bool
+
 endif # FTRACE
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index b8204ae93744..cece10b1f97c 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -111,4 +111,5 @@ obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o
 obj-$(CONFIG_RV) += rv/
 
 obj-$(CONFIG_TRACE_REMOTE) += trace_remote.o
+obj-$(CONFIG_SIMPLE_RING_BUFFER) += simple_ring_buffer.o
 libftrace-y := ftrace.o
diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c
new file mode 100644
index 000000000000..da9ea42b9926
--- /dev/null
+++ b/kernel/trace/simple_ring_buffer.c
@@ -0,0 +1,352 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 - Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <linux/atomic.h>
+#include <linux/simple_ring_buffer.h>
+
+#include <asm/barrier.h>
+#include <asm/local.h>
+
+#define SIMPLE_RB_LINK_HEAD	1UL
+#define SIMPLE_RB_LINK_MASK	~SIMPLE_RB_LINK_HEAD
+
+static bool simple_bpage_try_shunt_link(struct simple_buffer_page *bpage,
+					struct simple_buffer_page *dst,
+					unsigned long old_flags, unsigned long flags)
+{
+	unsigned long *ptr = (unsigned long *)(&bpage->list.next);
+	unsigned long old = (*ptr & SIMPLE_RB_LINK_MASK) | old_flags;
+	unsigned long new = (unsigned long)(&dst->list) | flags;
+
+	return cmpxchg(ptr, old, new) == old;
+}
+
+static void simple_bpage_set_link_flag(struct simple_buffer_page *bpage, unsigned long flag)
+{
+	bpage->list.next = (struct list_head *)
+		(((unsigned long)bpage->list.next & SIMPLE_RB_LINK_MASK) | flag);
+}
+
+static struct simple_buffer_page *simple_bpage_from_link(struct list_head *list)
+{
+	unsigned long ptr = (unsigned long)list & SIMPLE_RB_LINK_MASK;
+
+	return container_of((struct list_head *)ptr, struct simple_buffer_page, list);
+}
+
+static struct simple_buffer_page *simple_bpage_next_page(struct simple_buffer_page *bpage)
+{
+	return simple_bpage_from_link(bpage->list.next);
+}
+
+static bool simple_bpage_is_head(struct simple_buffer_page *bpage)
+{
+	return (unsigned long)bpage->list.prev->next & SIMPLE_RB_LINK_HEAD;
+}
+
+static void simple_bpage_reset(struct simple_buffer_page *bpage)
+{
+	bpage->write = 0;
+	bpage->entries = 0;
+
+	local_set(&bpage->page->commit, 0);
+}
+
+static void simple_bpage_init(struct simple_buffer_page *bpage, unsigned long page)
+{
+	INIT_LIST_HEAD(&bpage->list);
+	bpage->page = (struct buffer_data_page *)page;
+
+	simple_bpage_reset(bpage);
+}
+
+#define simple_rb_meta_inc(__meta, __inc)		\
+	WRITE_ONCE((__meta), (__meta + __inc))
+
+static bool simple_rb_loaded(struct simple_rb_per_cpu *cpu_buffer)
+{
+	return !!cpu_buffer->bpages;
+}
+
+int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer)
+{
+	struct simple_buffer_page *last, *head, *reader;
+	unsigned long overrun;
+
+	if (!simple_rb_loaded(cpu_buffer))
+		return -ENODEV;
+
+	head = cpu_buffer->head_page;
+	reader = cpu_buffer->reader_page;
+
+	do {
+		/* Run after the writer to find the head */
+		while (!simple_bpage_is_head(head))
+			cpu_buffer->head_page = head = simple_bpage_next_page(head);
+
+		/* Connect the reader page around the header page */
+		reader->list.next = head->list.next;
+		reader->list.prev = head->list.prev;
+
+		/* The last page before the head */
+		last = simple_bpage_from_link(head->list.prev);
+
+		/* The reader page points to the new header page */
+		simple_bpage_set_link_flag(reader, SIMPLE_RB_LINK_HEAD);
+
+		overrun = smp_load_acquire(&cpu_buffer->meta->overrun);
+	} while (!simple_bpage_try_shunt_link(last, reader, SIMPLE_RB_LINK_HEAD, 0));
+
+	cpu_buffer->head_page = simple_bpage_from_link(reader->list.next);
+	cpu_buffer->head_page->list.prev = &reader->list;
+	cpu_buffer->reader_page = head;
+	cpu_buffer->meta->reader.lost_events = overrun - cpu_buffer->last_overrun;
+	cpu_buffer->meta->reader.id = cpu_buffer->reader_page->id;
+	cpu_buffer->last_overrun = overrun;
+
+	return 0;
+}
+
+static struct simple_buffer_page *simple_rb_move_tail(struct simple_rb_per_cpu *cpu_buffer)
+{
+	struct simple_buffer_page *tail, *new_tail;
+
+	tail = cpu_buffer->tail_page;
+	new_tail = simple_bpage_next_page(tail);
+
+	if (simple_bpage_try_shunt_link(tail, new_tail, SIMPLE_RB_LINK_HEAD, 0)) {
+		/*
+		 * Oh no! we've caught the head. There is none anymore and swap_reader will spin
+		 * until we set the new one. Overrun must be written first, to make sure we report
+		 * the correct number of lost events.
+		 */
+		simple_rb_meta_inc(cpu_buffer->meta->overrun, new_tail->entries);
+		simple_rb_meta_inc(meta_pages_lost(cpu_buffer->meta), 1);
+
+		smp_store_release(&new_tail->list.next,
+				  (unsigned long)new_tail->list.next | SIMPLE_RB_LINK_HEAD);
+	}
+
+	simple_bpage_reset(new_tail);
+	cpu_buffer->tail_page = new_tail;
+
+	simple_rb_meta_inc(meta_pages_touched(cpu_buffer->meta), 1);
+
+	return new_tail;
+}
+
+static unsigned long rb_event_size(unsigned long length)
+{
+	struct ring_buffer_event *event;
+
+	return length + RB_EVNT_HDR_SIZE + sizeof(event->array[0]);
+}
+
+static struct ring_buffer_event *
+rb_event_add_ts_extend(struct ring_buffer_event *event, u64 delta)
+{
+	event->type_len = RINGBUF_TYPE_TIME_EXTEND;
+	event->time_delta = delta & TS_MASK;
+	event->array[0] = delta >> TS_SHIFT;
+
+	return (struct ring_buffer_event *)((unsigned long)event + 8);
+}
+
+static struct ring_buffer_event *
+simple_rb_reserve_next(struct simple_rb_per_cpu *cpu_buffer, unsigned long length, u64 timestamp)
+{
+	unsigned long ts_ext_size = 0, event_size = rb_event_size(length);
+	struct simple_buffer_page *tail = cpu_buffer->tail_page;
+	struct ring_buffer_event *event;
+	u32 write, prev_write;
+	u64 time_delta;
+
+	time_delta = timestamp - cpu_buffer->write_stamp;
+
+	if (test_time_stamp(time_delta))
+		ts_ext_size = 8;
+
+	prev_write = tail->write;
+	write = prev_write + event_size + ts_ext_size;
+
+	if (unlikely(write > (PAGE_SIZE - BUF_PAGE_HDR_SIZE)))
+		tail = simple_rb_move_tail(cpu_buffer);
+
+	if (!tail->entries) {
+		tail->page->time_stamp = timestamp;
+		time_delta = 0;
+		ts_ext_size = 0;
+		write = event_size;
+		prev_write = 0;
+	}
+
+	tail->write = write;
+	tail->entries++;
+
+	cpu_buffer->write_stamp = timestamp;
+
+	event = (struct ring_buffer_event *)(tail->page->data + prev_write);
+	if (ts_ext_size) {
+		event = rb_event_add_ts_extend(event, time_delta);
+		time_delta = 0;
+	}
+
+	event->type_len = 0;
+	event->time_delta = time_delta;
+	event->array[0] = event_size - RB_EVNT_HDR_SIZE;
+
+	return event;
+}
+
+void *simple_ring_buffer_reserve(struct simple_rb_per_cpu *cpu_buffer, unsigned long length,
+				 u64 timestamp)
+{
+	struct ring_buffer_event *rb_event;
+
+	if (cmpxchg(&cpu_buffer->status, SIMPLE_RB_READY, SIMPLE_RB_WRITING) != SIMPLE_RB_READY)
+		return NULL;
+
+	rb_event = simple_rb_reserve_next(cpu_buffer, length, timestamp);
+
+	return &rb_event->array[1];
+}
+
+void simple_ring_buffer_commit(struct simple_rb_per_cpu *cpu_buffer)
+{
+	local_set(&cpu_buffer->tail_page->page->commit,
+		  cpu_buffer->tail_page->write);
+	simple_rb_meta_inc(cpu_buffer->meta->entries, 1);
+
+	/*
+	 * Paired with simple_rb_enable_tracing() to ensure data is
+	 * written to the ring-buffer before teardown.
+	 */
+	smp_store_release(&cpu_buffer->status, SIMPLE_RB_READY);
+}
+
+static u32 simple_rb_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool enable)
+{
+	u32 prev_status;
+
+	if (enable)
+		return cmpxchg(&cpu_buffer->status, SIMPLE_RB_UNAVAILABLE, SIMPLE_RB_READY);
+
+	/* Wait for the buffer to be released */
+	do {
+		prev_status = cmpxchg_acquire(&cpu_buffer->status,
+					      SIMPLE_RB_READY,
+					      SIMPLE_RB_UNAVAILABLE);
+	} while (prev_status == SIMPLE_RB_WRITING);
+
+	return prev_status;
+}
+
+int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer)
+{
+	struct simple_buffer_page *bpage;
+	u32 prev_status;
+
+	if (!simple_rb_loaded(cpu_buffer))
+		return -ENODEV;
+
+	prev_status = simple_rb_enable_tracing(cpu_buffer, false);
+
+	while (!simple_bpage_is_head(cpu_buffer->head_page))
+		cpu_buffer->head_page = simple_bpage_next_page(cpu_buffer->head_page);
+
+	bpage = cpu_buffer->tail_page = cpu_buffer->head_page;
+	do {
+		simple_bpage_reset(bpage);
+		bpage = simple_bpage_next_page(bpage);
+	} while (bpage != cpu_buffer->head_page);
+
+	simple_bpage_reset(cpu_buffer->reader_page);
+
+	cpu_buffer->last_overrun = 0;
+	cpu_buffer->write_stamp = 0;
+
+	cpu_buffer->meta->reader.read = 0;
+	cpu_buffer->meta->reader.lost_events = 0;
+	cpu_buffer->meta->entries = 0;
+	cpu_buffer->meta->overrun = 0;
+	cpu_buffer->meta->read = 0;
+	meta_pages_lost(cpu_buffer->meta) = 0;
+	meta_pages_touched(cpu_buffer->meta) = 0;
+
+	if (prev_status == SIMPLE_RB_READY)
+		simple_rb_enable_tracing(cpu_buffer, true);
+
+	return 0;
+}
+
+int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_buffer_page *bpages,
+			    const struct ring_buffer_desc *desc)
+{
+	struct simple_buffer_page *bpage = bpages;
+	int i;
+
+	/* At least 1 reader page and one head */
+	if (desc->nr_page_va < 2)
+		return -EINVAL;
+
+	memset(cpu_buffer, 0, sizeof(*cpu_buffer));
+
+	cpu_buffer->bpages = bpages;
+
+	cpu_buffer->meta = (void *)desc->meta_va;
+	memset(cpu_buffer->meta, 0, sizeof(*cpu_buffer->meta));
+	cpu_buffer->meta->meta_page_size = PAGE_SIZE;
+	cpu_buffer->meta->nr_subbufs = cpu_buffer->nr_pages;
+
+	/* The reader page is not part of the ring initially */
+	simple_bpage_init(bpage, desc->page_va[0]);
+	bpage->id = 0;
+
+	cpu_buffer->nr_pages = 1;
+
+	cpu_buffer->reader_page = bpage;
+	cpu_buffer->tail_page = bpage + 1;
+	cpu_buffer->head_page = bpage + 1;
+
+	for (i = 1; i < desc->nr_page_va; i++) {
+		simple_bpage_init(++bpage, desc->page_va[i]);
+
+		bpage->list.next = &(bpage + 1)->list;
+		bpage->list.prev = &(bpage - 1)->list;
+		bpage->id = i;
+
+		cpu_buffer->nr_pages = i + 1;
+	}
+
+	/* Close the ring */
+	bpage->list.next = &cpu_buffer->tail_page->list;
+	cpu_buffer->tail_page->list.prev = &bpage->list;
+
+	/* The last init'ed page points to the head page */
+	simple_bpage_set_link_flag(bpage, SIMPLE_RB_LINK_HEAD);
+
+	return 0;
+}
+
+void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer)
+{
+	if (!simple_rb_loaded(cpu_buffer))
+		return;
+
+	simple_rb_enable_tracing(cpu_buffer, false);
+
+	cpu_buffer->bpages = 0;
+}
+
+int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool enable)
+{
+	if (!simple_rb_loaded(cpu_buffer))
+		return -ENODEV;
+
+	simple_rb_enable_tracing(cpu_buffer, enable);
+
+	return 0;
+}
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 10/24] tracing: Add a trace remote module for testing

[Vincent Donnefort]

Add a module to help testing the tracefs support for trace remotes. This
module:

  * Use simple_ring_buffer to write into a ring-buffer.
  * Declare a single "selftest" event that can be triggered from
    user-space.
  * Register a "test" trace remote.

This is intended to be used by trace remote selftests.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 407cb05cc8a0..2e27d9d1799e 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -1221,4 +1221,12 @@ config TRACE_REMOTE
 config SIMPLE_RING_BUFFER
 	bool
 
+config TRACE_REMOTE_TEST
+	tristate "Test module for remote tracing"
+	select TRACE_REMOTE
+	select SIMPLE_RING_BUFFER
+	help
+	  This trace remote includes a ring-buffer writer implementation using
+	  "simple_ring_buffer". This is solely intending for testing.
+
 endif # FTRACE
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index cece10b1f97c..8f5e194eba71 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -112,4 +112,6 @@ obj-$(CONFIG_RV) += rv/
 
 obj-$(CONFIG_TRACE_REMOTE) += trace_remote.o
 obj-$(CONFIG_SIMPLE_RING_BUFFER) += simple_ring_buffer.o
+obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test.o
+
 libftrace-y := ftrace.o
diff --git a/kernel/trace/remote_test.c b/kernel/trace/remote_test.c
new file mode 100644
index 000000000000..05556a879ba7
--- /dev/null
+++ b/kernel/trace/remote_test.c
@@ -0,0 +1,259 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 - Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <linux/module.h>
+#include <linux/simple_ring_buffer.h>
+#include <linux/trace_remote.h>
+#include <linux/tracefs.h>
+#include <linux/types.h>
+
+#define REMOTE_EVENT_INCLUDE_FILE kernel/trace/remote_test_events.h
+#include <trace/define_remote_events.h>
+
+static DEFINE_PER_CPU(struct simple_rb_per_cpu *, simple_rbs);
+static struct trace_buffer_desc *remote_test_buffer_desc;
+
+/*
+ * The trace_remote lock already serializes accesses from the trace_remote_callbacks.
+ * However write_event can still race with load/unload.
+ */
+static DEFINE_MUTEX(simple_rbs_lock);
+
+static int remote_test_load_simple_rb(int cpu, struct ring_buffer_desc *rb_desc)
+{
+	struct simple_rb_per_cpu *cpu_buffer;
+	struct simple_buffer_page *bpages;
+	int ret = -ENOMEM;
+
+	cpu_buffer = kzalloc(sizeof(*cpu_buffer), GFP_KERNEL);
+	if (!cpu_buffer)
+		return ret;
+
+	bpages = kmalloc_array(rb_desc->nr_page_va, sizeof(*bpages), GFP_KERNEL);
+	if (!bpages)
+		goto err_free_cpu_buffer;
+
+	ret = simple_ring_buffer_init(cpu_buffer, bpages, rb_desc);
+	if (ret)
+		goto err_free_bpages;
+
+	guard(mutex)(&simple_rbs_lock);
+
+	*per_cpu_ptr(&simple_rbs, cpu) = cpu_buffer;
+
+	return 0;
+
+err_free_bpages:
+	kfree(bpages);
+
+err_free_cpu_buffer:
+	kfree(cpu_buffer);
+
+	return ret;
+}
+
+static void remote_test_unload_simple_rb(int cpu)
+{
+	struct simple_rb_per_cpu *cpu_buffer = *per_cpu_ptr(&simple_rbs, cpu);
+	struct simple_buffer_page *bpages;
+
+	if (!cpu_buffer)
+		return;
+
+	guard(mutex)(&simple_rbs_lock);
+
+	bpages = cpu_buffer->bpages;
+	simple_ring_buffer_unload(cpu_buffer);
+	kfree(bpages);
+	kfree(cpu_buffer);
+	*per_cpu_ptr(&simple_rbs, cpu) = NULL;
+}
+
+static struct trace_buffer_desc *remote_test_load(unsigned long size, void *unused)
+{
+	struct ring_buffer_desc *rb_desc;
+	struct trace_buffer_desc *desc;
+	size_t desc_size;
+	int cpu, ret;
+
+	if (WARN_ON(remote_test_buffer_desc))
+		return NULL;
+
+	cpus_read_lock();
+
+	desc_size = trace_buffer_desc_size(size, num_online_cpus());
+	if (desc_size == SIZE_MAX)
+		goto err_unlock_cpus;
+
+	desc = kmalloc(desc_size, GFP_KERNEL);
+	if (!desc)
+		goto err_unlock_cpus;
+
+	ret = trace_remote_alloc_buffer(desc, size, cpu_online_mask);
+	if (ret)
+		goto err_free_desc;
+
+	for_each_ring_buffer_desc(rb_desc, cpu, desc) {
+		ret = remote_test_load_simple_rb(rb_desc->cpu, rb_desc);
+		if (ret)
+			goto err;
+	}
+
+	remote_test_buffer_desc = desc;
+
+	cpus_read_unlock();
+
+	return remote_test_buffer_desc;
+
+err:
+	for_each_ring_buffer_desc(rb_desc, cpu, remote_test_buffer_desc)
+		remote_test_unload_simple_rb(rb_desc->cpu);
+	trace_remote_free_buffer(remote_test_buffer_desc);
+
+err_free_desc:
+	kfree(desc);
+
+err_unlock_cpus:
+	cpus_read_unlock();
+
+	return NULL;
+}
+
+static void remote_test_unload(struct trace_buffer_desc *desc, void *unused)
+{
+	struct ring_buffer_desc *rb_desc;
+	int cpu;
+
+	if (WARN_ON(desc != remote_test_buffer_desc))
+		return;
+
+	for_each_ring_buffer_desc(rb_desc, cpu, desc)
+		remote_test_unload_simple_rb(rb_desc->cpu);
+
+	remote_test_buffer_desc = NULL;
+	trace_remote_free_buffer(desc);
+}
+
+static int remote_test_enable_tracing(bool enable, void *unused)
+{
+	struct ring_buffer_desc *rb_desc;
+	int cpu;
+
+	if (!remote_test_buffer_desc)
+		return -ENODEV;
+
+	for_each_ring_buffer_desc(rb_desc, cpu, remote_test_buffer_desc)
+		WARN_ON(simple_ring_buffer_enable_tracing(*per_cpu_ptr(&simple_rbs, rb_desc->cpu),
+							  enable));
+	return 0;
+}
+
+static int remote_test_swap_reader_page(unsigned int cpu, void *unused)
+{
+	struct simple_rb_per_cpu *cpu_buffer;
+
+	if (cpu >= NR_CPUS)
+		return -EINVAL;
+
+	cpu_buffer = *per_cpu_ptr(&simple_rbs, cpu);
+	if (!cpu_buffer)
+		return -EINVAL;
+
+	return simple_ring_buffer_swap_reader_page(cpu_buffer);
+}
+
+static int remote_test_reset(unsigned int cpu, void *unused)
+{
+	struct simple_rb_per_cpu *cpu_buffer;
+
+	if (cpu >= NR_CPUS)
+		return -EINVAL;
+
+	cpu_buffer = *per_cpu_ptr(&simple_rbs, cpu);
+	if (!cpu_buffer)
+		return -EINVAL;
+
+	return simple_ring_buffer_reset(cpu_buffer);
+}
+
+static int remote_test_enable_event(unsigned short id, bool enable, void *unused)
+{
+	if (id != REMOTE_TEST_EVENT_ID)
+		return -EINVAL;
+
+	/*
+	 * Let's just use the struct remote_event enabled field that is turned on and off by
+	 * trace_remote. This is a bit racy but good enough for a simple test module.
+	 */
+	return 0;
+}
+
+static ssize_t
+write_event_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *pos)
+{
+	struct remote_event_format_selftest *evt_test;
+	struct simple_rb_per_cpu *cpu_buffer;
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+	if (ret)
+		return ret;
+
+	guard(mutex)(&simple_rbs_lock);
+
+	if (!remote_event_selftest.enabled)
+		return cnt;
+
+	cpu_buffer = *this_cpu_ptr(&simple_rbs);
+	if (!cpu_buffer)
+		return -ENODEV;
+
+	evt_test = simple_ring_buffer_reserve(cpu_buffer,
+					      sizeof(struct remote_event_format_selftest),
+					      trace_clock_global());
+	if (!evt_test)
+		return -ENODEV;
+
+	evt_test->hdr.id = REMOTE_TEST_EVENT_ID;
+	evt_test->id = val;
+
+	simple_ring_buffer_commit(cpu_buffer);
+
+	return cnt;
+}
+
+static const struct file_operations write_event_fops = {
+	.write	= write_event_write,
+};
+
+static int remote_test_init_tracefs(struct dentry *d, void *unused)
+{
+	return tracefs_create_file("write_event", 0200, d, NULL, &write_event_fops) ?
+		0 : -ENOMEM;
+}
+
+static struct trace_remote_callbacks trace_remote_callbacks = {
+	.init			= remote_test_init_tracefs,
+	.load_trace_buffer	= remote_test_load,
+	.unload_trace_buffer	= remote_test_unload,
+	.enable_tracing		= remote_test_enable_tracing,
+	.swap_reader_page	= remote_test_swap_reader_page,
+	.reset			= remote_test_reset,
+	.enable_event		= remote_test_enable_event,
+};
+
+static int __init remote_test_init(void)
+{
+	return trace_remote_register("test", &trace_remote_callbacks, NULL,
+				     &remote_event_selftest, 1);
+}
+
+module_init(remote_test_init);
+
+MODULE_DESCRIPTION("Test module for the trace remote interface");
+MODULE_AUTHOR("Vincent Donnefort");
+MODULE_LICENSE("GPL");
diff --git a/kernel/trace/remote_test_events.h b/kernel/trace/remote_test_events.h
new file mode 100644
index 000000000000..bb68aac4a25c
--- /dev/null
+++ b/kernel/trace/remote_test_events.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#define REMOTE_TEST_EVENT_ID 1
+
+REMOTE_EVENT(selftest, REMOTE_TEST_EVENT_ID,
+	RE_STRUCT(
+		re_field(u64, id)
+	),
+	RE_PRINTK("id=%lld", __entry->id)
+);
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 11/24] tracing: selftests: Add trace remote tests

[Vincent Donnefort]

Exercise the tracefs interface for trace remote with a set of tests to
check:

  * loading/unloading (unloading.tc)
  * reset (reset.tc)
  * size changes (buffer_size.tc)
  * event integrity (trace_pipe)

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc b/tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc
new file mode 100644
index 000000000000..60bf431ccc91
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc
@@ -0,0 +1,24 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote buffer size
+
+. $TEST_DIR/remotes/functions
+
+test_buffer_size()
+{
+    echo 0 > tracing_on
+    assert_unloaded
+
+    echo 4096 > buffer_size_kb
+    echo 1 > tracing_on
+    assert_loaded
+
+    echo 0 > tracing_on
+    echo 7 > buffer_size_kb
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+    set -e
+    setup_remote_test
+    test_buffer_size
+fi
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/functions b/tools/testing/selftests/ftrace/test.d/remotes/functions
new file mode 100644
index 000000000000..504a495b3b1b
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/functions
@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: GPL-2.0
+
+setup_remote()
+{
+	local name=$1
+
+	[ -e $TRACING_DIR/remotes/$name/write_event ] || exit_unresolved
+
+	cd remotes/$name/
+	echo 0 > tracing_on
+	clear_trace
+	echo 7 > buffer_size_kb
+	echo 0 > events/enable
+	echo 1 > events/$name/selftest/enable
+	echo 1 > tracing_on
+}
+
+setup_remote_test()
+{
+	[ -d $TRACING_DIR/remotes/test/ ] || modprobe remote_test || exit_unresolved
+
+	setup_remote "test"
+}
+
+assert_loaded()
+{
+	grep -q "(loaded)" buffer_size_kb
+}
+
+assert_unloaded()
+{
+	grep -q "(unloaded)" buffer_size_kb
+}
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/reset.tc b/tools/testing/selftests/ftrace/test.d/remotes/reset.tc
new file mode 100644
index 000000000000..93d6eb2a807f
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/reset.tc
@@ -0,0 +1,105 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote reset
+
+. $TEST_DIR/remotes/functions
+
+get_cpu_ids()
+{
+    sed -n 's/^processor\s*:\s*\([0-9]\+\).*/\1/p' /proc/cpuinfo
+}
+
+dump_trace()
+{
+    output=$(mktemp /tmp/remote_test.XXXXXX)
+    cat trace_pipe > $output &
+    pid=$!
+    sleep 1
+    kill -1 $pid
+
+    echo $output
+}
+
+check_reset()
+{
+    write_event_path="write_event"
+    taskset=""
+
+    clear_trace
+
+    # Is the buffer empty?
+    output=$(dump_trace)
+    test $(wc -l $output | cut -d ' ' -f1) -eq 0
+
+    if $(echo $(pwd) | grep -q "per_cpu/cpu"); then
+        write_event_path="../../write_event"
+        cpu_id=$(echo $(pwd) | sed -e 's/.*per_cpu\/cpu//')
+        taskset="taskset -c $cpu_id"
+    fi
+    rm $output
+
+    # Can we properly write a new event?
+    $taskset echo 7890 > $write_event_path
+    output=$(dump_trace)
+    test $(wc -l $output | cut -d ' ' -f1) -eq 1
+    grep -q "id=7890" $output
+    rm $output
+}
+
+test_global_interface()
+{
+    output=$(mktemp /tmp/remote_test.XXXXXX)
+
+    # Confidence check
+    echo 123456 > write_event
+    output=$(dump_trace)
+    grep -q "id=123456" $output
+    rm $output
+
+    # Reset single event
+    echo 1 > write_event
+    check_reset
+
+    # Reset lost events
+    for i in $(seq 1 10000); do
+        echo 1 > write_event
+    done
+    check_reset
+}
+
+test_percpu_interface()
+{
+    [ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 0
+
+    for cpu in $(get_cpu_ids); do
+        taskset -c $cpu echo 1 > write_event
+    done
+
+    check_non_empty=0
+    for cpu in $(get_cpu_ids); do
+        cd per_cpu/cpu$cpu/
+
+        if [ $check_non_empty -eq 0 ]; then
+            check_reset
+            check_non_empty=1
+        else
+            # Check we have only reset 1 CPU
+            output=$(dump_trace)
+            test $(wc -l $output | cut -d ' ' -f1) -eq 1
+            rm $output
+        fi
+        cd -
+    done
+}
+
+test_reset()
+{
+    test_global_interface
+    test_percpu_interface
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+    set -e
+    setup_remote_test
+    test_reset
+fi
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc b/tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc
new file mode 100644
index 000000000000..f4bd2b3655e0
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc
@@ -0,0 +1,57 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote trace_pipe
+
+. $TEST_DIR/remotes/functions
+
+test_trace_pipe()
+{
+    echo 0 > tracing_on
+    assert_unloaded
+
+    echo 1024 > buffer_size_kb
+    echo 1 > tracing_on
+    assert_loaded
+
+    output=$(mktemp /tmp/remote_test.XXXXXX)
+
+    cat trace_pipe > $output &
+    pid=$!
+
+    for i in $(seq 1 1000); do
+        echo $i > write_event
+    done
+
+    echo 0 > tracing_on
+    sleep 1
+    kill $pid
+
+    prev_ts=0 # TODO: Init with proper clock value
+    prev_id=0
+
+    # Only keep <timestamp> <id>
+    sed -i -e 's/\[[0-9]*\]\s*\([0-9]*.[0-9]*\): [a-z]* id=\([0-9]*\)/\1 \2/' $output
+
+    IFS=$'\n'
+    for line in $(cat $output); do
+        ts=$(echo $line | cut -d ' ' -f 1)
+        id=$(echo $line | cut -d ' ' -f 2)
+
+        test $(echo "$ts>$prev_ts" | bc) -eq 1
+        test $id -eq $((prev_id + 1))
+
+        prev_ts=$ts
+        prev_id=$id
+    done
+
+    test $prev_id -eq 1000
+
+    rm $output
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+    set -e
+
+    setup_remote_test
+    test_trace_pipe
+fi
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/unloading.tc b/tools/testing/selftests/ftrace/test.d/remotes/unloading.tc
new file mode 100644
index 000000000000..05bb21f80e34
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/unloading.tc
@@ -0,0 +1,36 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote unloading
+
+. $TEST_DIR/remotes/functions
+
+test_unloading()
+{
+    # No reader, writing
+    assert_loaded
+
+    # No reader, no writing
+    echo 0 > tracing_on
+    assert_unloaded
+
+    # 1 reader, no writing
+    cat trace_pipe &
+    pid=$!
+    sleep 1
+    assert_loaded
+    kill $pid
+    assert_unloaded
+
+    # No reader, no writing, events
+    echo 1 > tracing_on
+    echo 1 > write_event
+    echo 0 > tracing_on
+    assert_loaded
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+    set -e
+
+    setup_remote_test
+    test_unloading
+fi
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 12/24] tracing: load/unload page callbacks for simple_ring_buffer

[Vincent Donnefort]

Add load/unload callback used for each admitted page in the ring-buffer.
This will be later useful for the pKVM hypervisor which uses a different
VA space and need to dynamically map/unmap the ring-buffer pages.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/simple_ring_buffer.h b/include/linux/simple_ring_buffer.h
index 6cf8486d46e2..10e385d347a0 100644
--- a/include/linux/simple_ring_buffer.h
+++ b/include/linux/simple_ring_buffer.h
@@ -46,4 +46,12 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool enable);
 int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer);
 int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer);
+
+int __simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer,
+			      struct simple_buffer_page *bpages,
+			      const struct ring_buffer_desc *desc,
+			      void *(*load_page)(unsigned long va),
+			      void (*unload_page)(void *va));
+void __simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer,
+				 void (*unload_page)(void *));
 #endif
diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c
index da9ea42b9926..54c8f221f693 100644
--- a/kernel/trace/simple_ring_buffer.c
+++ b/kernel/trace/simple_ring_buffer.c
@@ -55,7 +55,7 @@ static void simple_bpage_reset(struct simple_buffer_page *bpage)
 	local_set(&bpage->page->commit, 0);
 }
 
-static void simple_bpage_init(struct simple_buffer_page *bpage, unsigned long page)
+static void simple_bpage_init(struct simple_buffer_page *bpage, void *page)
 {
 	INIT_LIST_HEAD(&bpage->list);
 	bpage->page = (struct buffer_data_page *)page;
@@ -282,10 +282,14 @@ int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer)
 	return 0;
 }
 
-int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_buffer_page *bpages,
-			    const struct ring_buffer_desc *desc)
+int __simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_buffer_page *bpages,
+			      const struct ring_buffer_desc *desc,
+			      void *(*load_page)(unsigned long va),
+			      void (*unload_page)(void *va))
 {
 	struct simple_buffer_page *bpage = bpages;
+	int ret = 0;
+	void *page;
 	int i;
 
 	/* At least 1 reader page and one head */
@@ -294,15 +298,22 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 
 	memset(cpu_buffer, 0, sizeof(*cpu_buffer));
 
-	cpu_buffer->bpages = bpages;
+	cpu_buffer->meta = load_page(desc->meta_va);
+	if (!cpu_buffer->meta)
+		return -EINVAL;
 
-	cpu_buffer->meta = (void *)desc->meta_va;
 	memset(cpu_buffer->meta, 0, sizeof(*cpu_buffer->meta));
 	cpu_buffer->meta->meta_page_size = PAGE_SIZE;
 	cpu_buffer->meta->nr_subbufs = cpu_buffer->nr_pages;
 
 	/* The reader page is not part of the ring initially */
-	simple_bpage_init(bpage, desc->page_va[0]);
+	page = load_page(desc->page_va[0]);
+	if (!page) {
+		unload_page(cpu_buffer->meta);
+		return -EINVAL;
+	}
+
+	simple_bpage_init(bpage, page);
 	bpage->id = 0;
 
 	cpu_buffer->nr_pages = 1;
@@ -312,7 +323,13 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 	cpu_buffer->head_page = bpage + 1;
 
 	for (i = 1; i < desc->nr_page_va; i++) {
-		simple_bpage_init(++bpage, desc->page_va[i]);
+		page = load_page(desc->page_va[i]);
+		if (!page) {
+			ret = -EINVAL;
+			break;
+		}
+
+		simple_bpage_init(++bpage, page);
 
 		bpage->list.next = &(bpage + 1)->list;
 		bpage->list.prev = &(bpage - 1)->list;
@@ -321,6 +338,14 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 		cpu_buffer->nr_pages = i + 1;
 	}
 
+	if (ret) {
+		for (i--; i >= 0; i--)
+			unload_page((void *)desc->page_va[i]);
+		unload_page(cpu_buffer->meta);
+
+		return ret;
+	}
+
 	/* Close the ring */
 	bpage->list.next = &cpu_buffer->tail_page->list;
 	cpu_buffer->tail_page->list.prev = &bpage->list;
@@ -328,19 +353,46 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 	/* The last init'ed page points to the head page */
 	simple_bpage_set_link_flag(bpage, SIMPLE_RB_LINK_HEAD);
 
+	cpu_buffer->bpages = bpages;
+
 	return 0;
 }
 
-void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer)
+static void *__load_page(unsigned long page)
 {
+	return (void *)page;
+}
+
+static void __unload_page(void *page) { }
+
+int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_buffer_page *bpages,
+			    const struct ring_buffer_desc *desc)
+{
+	return __simple_ring_buffer_init(cpu_buffer, bpages, desc, __load_page, __unload_page);
+}
+
+void __simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer,
+				 void (*unload_page)(void *))
+{
+	int p;
+
 	if (!simple_rb_loaded(cpu_buffer))
 		return;
 
 	simple_rb_enable_tracing(cpu_buffer, false);
 
+	unload_page(cpu_buffer->meta);
+	for (p = 0; p < cpu_buffer->nr_pages; p++)
+		unload_page(cpu_buffer->bpages[p].page);
+
 	cpu_buffer->bpages = 0;
 }
 
+void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer)
+{
+	return __simple_ring_buffer_unload(cpu_buffer, __unload_page);
+}
+
 int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool enable)
 {
 	if (!simple_rb_loaded(cpu_buffer))
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 13/24] tracing: Check for undefined symbols in simple_ring_buffer

[Vincent Donnefort]

The simple_ring_buffer implementation must remain simple enough to be
used by the pKVM hypervisor. Prevent the object build if unresolved
symbols are found.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 8f5e194eba71..a2f1489e11af 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -114,4 +114,19 @@ obj-$(CONFIG_TRACE_REMOTE) += trace_remote.o
 obj-$(CONFIG_SIMPLE_RING_BUFFER) += simple_ring_buffer.o
 obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test.o
 
+#
+# simple_ring_buffer is used by the pKVM hypervisor which does not have access
+# to all kernel symbols. Fail the build if forbidden symbols are found.
+#
+UNDEFINED_ALLOWLIST := alt_cb_patch_nops
+UNDEFINED_ALLOWLIST := $(addprefix -e , $(UNDEFINED_ALLOWLIST))
+
+quiet_cmd_check_undefined = NM      $<
+      cmd_check_undefined = test -z "`$(NM) -u $< | grep -v $(UNDEFINED_ALLOWLIST)`"
+
+$(obj)/%.o.checked: $(obj)/%.o FORCE
+	$(call if_changed,check_undefined)
+
+always-$(CONFIG_SIMPLE_RING_BUFFER) +=  simple_ring_buffer.o.checked
+
 libftrace-y := ftrace.o
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 14/24] KVM: arm64: Support unaligned fixmap in the nVHE hyp

[Vincent Donnefort]

Return the fixmap VA with the page offset, instead of the page base
address. This allows to use hyp_fixmap_map() seamlessly regardless of
the address alignment.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
index f41c7440b34b..720cc3b36596 100644
--- a/arch/arm64/kvm/hyp/nvhe/mm.c
+++ b/arch/arm64/kvm/hyp/nvhe/mm.c
@@ -240,7 +240,7 @@ void *hyp_fixmap_map(phys_addr_t phys)
 	WRITE_ONCE(*ptep, pte);
 	dsb(ishst);
 
-	return (void *)slot->addr;
+	return (void *)slot->addr + offset_in_page(phys);
 }
 
 static void fixmap_clear_slot(struct hyp_fixmap_slot *slot)
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 15/24] KVM: arm64: Add .hyp.data section

[Vincent Donnefort]

Allow the init of non-zero data in the pKVM hypervisor by adding support
for the .data section.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/include/asm/sections.h b/arch/arm64/include/asm/sections.h
index 40971ac1303f..51b0d594239e 100644
--- a/arch/arm64/include/asm/sections.h
+++ b/arch/arm64/include/asm/sections.h
@@ -11,6 +11,7 @@ extern char __alt_instructions[], __alt_instructions_end[];
 extern char __hibernate_exit_text_start[], __hibernate_exit_text_end[];
 extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[];
 extern char __hyp_text_start[], __hyp_text_end[];
+extern char __hyp_data_start[], __hyp_data_end[];
 extern char __hyp_rodata_start[], __hyp_rodata_end[];
 extern char __hyp_reloc_begin[], __hyp_reloc_end[];
 extern char __hyp_bss_start[], __hyp_bss_end[];
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index 5e3c4b58f279..9c5345f1ab66 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -131,6 +131,8 @@ KVM_NVHE_ALIAS(__hyp_text_start);
 KVM_NVHE_ALIAS(__hyp_text_end);
 KVM_NVHE_ALIAS(__hyp_bss_start);
 KVM_NVHE_ALIAS(__hyp_bss_end);
+KVM_NVHE_ALIAS(__hyp_data_start);
+KVM_NVHE_ALIAS(__hyp_data_end);
 KVM_NVHE_ALIAS(__hyp_rodata_start);
 KVM_NVHE_ALIAS(__hyp_rodata_end);
 
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index e73326bd3ff7..7c770053f072 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -13,7 +13,7 @@
 	*(__kvm_ex_table)					\
 	__stop___kvm_ex_table = .;
 
-#define HYPERVISOR_DATA_SECTIONS				\
+#define HYPERVISOR_RODATA_SECTIONS				\
 	HYP_SECTION_NAME(.rodata) : {				\
 		. = ALIGN(PAGE_SIZE);				\
 		__hyp_rodata_start = .;				\
@@ -23,6 +23,15 @@
 		__hyp_rodata_end = .;				\
 	}
 
+#define HYPERVISOR_DATA_SECTION					\
+	HYP_SECTION_NAME(.data) : {				\
+		. = ALIGN(PAGE_SIZE);				\
+		__hyp_data_start = .;				\
+		*(HYP_SECTION_NAME(.data))			\
+		. = ALIGN(PAGE_SIZE);				\
+		__hyp_data_end = .;				\
+	}
+
 #define HYPERVISOR_PERCPU_SECTION				\
 	. = ALIGN(PAGE_SIZE);					\
 	HYP_SECTION_NAME(.data..percpu) : {			\
@@ -51,7 +60,8 @@
 #define SBSS_ALIGN			PAGE_SIZE
 #else /* CONFIG_KVM */
 #define HYPERVISOR_EXTABLE
-#define HYPERVISOR_DATA_SECTIONS
+#define HYPERVISOR_RODATA_SECTIONS
+#define HYPERVISOR_DATA_SECTION
 #define HYPERVISOR_PERCPU_SECTION
 #define HYPERVISOR_RELOC_SECTION
 #define SBSS_ALIGN			0
@@ -190,7 +200,7 @@ SECTIONS
 	/* everything from this point to __init_begin will be marked RO NX */
 	RO_DATA(PAGE_SIZE)
 
-	HYPERVISOR_DATA_SECTIONS
+	HYPERVISOR_RODATA_SECTIONS
 
 	.got : { *(.got) }
 	/*
@@ -295,6 +305,8 @@ SECTIONS
 	_sdata = .;
 	RW_DATA(L1_CACHE_BYTES, PAGE_SIZE, THREAD_ALIGN)
 
+	HYPERVISOR_DATA_SECTION
+
 	/*
 	 * Data written with the MMU off but read with the MMU on requires
 	 * cache lines to be invalidated, discarding up to a Cache Writeback
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 68fec8c95fee..58e8119f66bd 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2604,6 +2604,13 @@ static int __init init_hyp_mode(void)
 		goto out_err;
 	}
 
+	err = create_hyp_mappings(kvm_ksym_ref(__hyp_data_start),
+				  kvm_ksym_ref(__hyp_data_end), PAGE_HYP);
+	if (err) {
+		kvm_err("Cannot map .hyp.data section\n");
+		goto out_err;
+	}
+
 	err = create_hyp_mappings(kvm_ksym_ref(__hyp_rodata_start),
 				  kvm_ksym_ref(__hyp_rodata_end), PAGE_HYP_RO);
 	if (err) {
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
index f4562f417d3f..d724f6d69302 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
@@ -25,5 +25,7 @@ SECTIONS {
 	BEGIN_HYP_SECTION(.data..percpu)
 		PERCPU_INPUT(L1_CACHE_BYTES)
 	END_HYP_SECTION
+
 	HYP_SECTION(.bss)
+	HYP_SECTION(.data)
 }
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index d62bcb5634a2..46d9bd04348f 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -119,6 +119,10 @@ static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
 	if (ret)
 		return ret;
 
+	ret = pkvm_create_mappings(__hyp_data_start, __hyp_data_end, PAGE_HYP);
+	if (ret)
+		return ret;
+
 	ret = pkvm_create_mappings(__hyp_rodata_start, __hyp_rodata_end, PAGE_HYP_RO);
 	if (ret)
 		return ret;
diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index 0f89157d31fd..c462140e640a 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -262,6 +262,7 @@ static int __init finalize_pkvm(void)
 	 * at, which would end badly once inaccessible.
 	 */
 	kmemleak_free_part(__hyp_bss_start, __hyp_bss_end - __hyp_bss_start);
+	kmemleak_free_part(__hyp_data_start, __hyp_data_end - __hyp_data_start);
 	kmemleak_free_part(__hyp_rodata_start, __hyp_rodata_end - __hyp_rodata_start);
 	kmemleak_free_part_phys(hyp_mem_base, hyp_mem_size);
 
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 16/24] KVM: arm64: Add clock support for the pKVM hyp

[Vincent Donnefort]

By default, the arm64 host kernel is using the arch timer as a source
for sched_clock. Conveniently, EL2 has access to that same counter,
allowing to generate clock values that are synchronized.

The clock needs nonetheless to be setup with the same slope values as
the kernel. Introducing at the same time trace_clock() which is expected
to be later configured by the hypervisor tracing.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
index e6be1f5d0967..d46621d936e3 100644
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -146,5 +146,4 @@ extern u64 kvm_nvhe_sym(id_aa64smfr0_el1_sys_val);
 extern unsigned long kvm_nvhe_sym(__icache_flags);
 extern unsigned int kvm_nvhe_sym(kvm_arm_vmid_bits);
 extern unsigned int kvm_nvhe_sym(kvm_host_sve_max_vl);
-
 #endif /* __ARM64_KVM_HYP_H__ */
diff --git a/arch/arm64/kvm/hyp/include/nvhe/clock.h b/arch/arm64/kvm/hyp/include/nvhe/clock.h
new file mode 100644
index 000000000000..9e152521f345
--- /dev/null
+++ b/arch/arm64/kvm/hyp/include/nvhe/clock.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM64_KVM_HYP_NVHE_CLOCK_H
+#define __ARM64_KVM_HYP_NVHE_CLOCK_H
+#include <linux/types.h>
+
+#include <asm/kvm_hyp.h>
+
+#ifdef CONFIG_PKVM_TRACING
+void trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc);
+u64 trace_clock(void);
+#else
+static inline void
+trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc) { }
+static inline u64 trace_clock(void) { return 0; }
+#endif
+#endif
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index b43426a493df..68d14258165c 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -28,6 +28,7 @@ hyp-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o
 hyp-obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
 	 ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
 hyp-obj-$(CONFIG_LIST_HARDENED) += list_debug.o
+hyp-obj-$(CONFIG_PKVM_TRACING) += clock.o
 hyp-obj-y += $(lib-objs)
 
 ##
diff --git a/arch/arm64/kvm/hyp/nvhe/clock.c b/arch/arm64/kvm/hyp/nvhe/clock.c
new file mode 100644
index 000000000000..879c6b09d9ca
--- /dev/null
+++ b/arch/arm64/kvm/hyp/nvhe/clock.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <nvhe/clock.h>
+
+#include <asm/arch_timer.h>
+#include <asm/div64.h>
+
+static struct clock_data {
+	struct {
+		u32 mult;
+		u32 shift;
+		u64 epoch_ns;
+		u64 epoch_cyc;
+		u64 cyc_overflow64;
+	} data[2];
+	u64 cur;
+} trace_clock_data;
+
+static u64 __clock_mult_uint128(u64 cyc, u32 mult, u32 shift)
+{
+	__uint128_t ns = (__uint128_t)cyc * mult;
+
+	ns >>= shift;
+
+	return (u64)ns;
+}
+
+/* Does not guarantee no reader on the modified bank. */
+void trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
+{
+	struct clock_data *clock = &trace_clock_data;
+	u64 bank = clock->cur ^ 1;
+
+	clock->data[bank].mult			= mult;
+	clock->data[bank].shift			= shift;
+	clock->data[bank].epoch_ns		= epoch_ns;
+	clock->data[bank].epoch_cyc		= epoch_cyc;
+	clock->data[bank].cyc_overflow64	= ULONG_MAX / mult;
+
+	smp_store_release(&clock->cur, bank);
+}
+
+/* Using host provided data. Do not use for anything else than debugging. */
+u64 trace_clock(void)
+{
+	struct clock_data *clock = &trace_clock_data;
+	u64 bank = smp_load_acquire(&clock->cur);
+	u64 cyc, ns;
+
+	cyc = __arch_counter_get_cntpct() - clock->data[bank].epoch_cyc;
+
+	if (likely(cyc < clock->data[bank].cyc_overflow64)) {
+		ns = cyc * clock->data[bank].mult;
+		ns >>= clock->data[bank].shift;
+	} else {
+		ns = __clock_mult_uint128(cyc, clock->data[bank].mult,
+					   clock->data[bank].shift);
+	}
+
+	return (u64)ns + clock->data[bank].epoch_ns;
+}
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 17/24] KVM: arm64: Add tracing capability for the pKVM hyp

[Vincent Donnefort]

When running with protected mode, the host has very little knowledge
about what is happening in the hypervisor. Of course this is an
essential feature for security but nonetheless, that piece of code
growing with more responsibilities, we need now a way to debug and
profile it. Tracefs by its reliability, versatility and support for
user-space is the perfect tool.

There's no way the hypervisor could log events directly into the host
tracefs ring-buffers. So instead let's use our own, where the hypervisor
is the writer and the host the reader.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index bec227f9500a..437ac948d136 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -87,6 +87,10 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_load,
 	__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_put,
 	__KVM_HOST_SMCCC_FUNC___pkvm_tlb_flush_vmid,
+	__KVM_HOST_SMCCC_FUNC___pkvm_load_tracing,
+	__KVM_HOST_SMCCC_FUNC___pkvm_unload_tracing,
+	__KVM_HOST_SMCCC_FUNC___pkvm_enable_tracing,
+	__KVM_HOST_SMCCC_FUNC___pkvm_swap_reader_tracing,
 };
 
 #define DECLARE_KVM_VHE_SYM(sym)	extern char sym[]
diff --git a/arch/arm64/include/asm/kvm_hyptrace.h b/arch/arm64/include/asm/kvm_hyptrace.h
new file mode 100644
index 000000000000..9c30a479bc36
--- /dev/null
+++ b/arch/arm64/include/asm/kvm_hyptrace.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ARM64_KVM_HYPTRACE_H_
+#define __ARM64_KVM_HYPTRACE_H_
+
+#include <linux/ring_buffer.h>
+
+struct hyp_trace_desc {
+	unsigned long			bpages_backing_start;
+	size_t				bpages_backing_size;
+	struct trace_buffer_desc	trace_buffer_desc;
+
+};
+#endif
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 096e45acadb2..f65eba00c1c9 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -83,4 +83,11 @@ config PTDUMP_STAGE2_DEBUGFS
 
 	  If in doubt, say N.
 
+config PKVM_TRACING
+	bool
+	depends on KVM
+	depends on TRACING
+	select SIMPLE_RING_BUFFER
+	default y
+
 endif # VIRTUALIZATION
diff --git a/arch/arm64/kvm/hyp/include/nvhe/trace.h b/arch/arm64/kvm/hyp/include/nvhe/trace.h
new file mode 100644
index 000000000000..996e90c0974f
--- /dev/null
+++ b/arch/arm64/kvm/hyp/include/nvhe/trace.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ARM64_KVM_HYP_NVHE_TRACE_H
+#define __ARM64_KVM_HYP_NVHE_TRACE_H
+#include <asm/kvm_hyptrace.h>
+
+#ifdef CONFIG_PKVM_TRACING
+void *tracing_reserve_entry(unsigned long length);
+void tracing_commit_entry(void);
+
+int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size);
+void __pkvm_unload_tracing(void);
+int __pkvm_enable_tracing(bool enable);
+int __pkvm_swap_reader_tracing(unsigned int cpu);
+#else
+static inline void *tracing_reserve_entry(unsigned long length) { return NULL; }
+static inline void tracing_commit_entry(void) { }
+
+static inline int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size) { return -ENODEV; }
+static inline void __pkvm_unload_tracing(void) { }
+static inline int __pkvm_enable_tracing(bool enable) { return -ENODEV; }
+static inline int __pkvm_swap_reader_tracing(unsigned int cpu) { return -ENODEV; }
+#endif
+#endif
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index 68d14258165c..6d92f58aea7e 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -28,7 +28,7 @@ hyp-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o
 hyp-obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
 	 ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
 hyp-obj-$(CONFIG_LIST_HARDENED) += list_debug.o
-hyp-obj-$(CONFIG_PKVM_TRACING) += clock.o
+hyp-obj-$(CONFIG_PKVM_TRACING) += clock.o trace.o ../../../../../kernel/trace/simple_ring_buffer.o
 hyp-obj-y += $(lib-objs)
 
 ##
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 2c37680d954c..68b98547666b 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -18,6 +18,7 @@
 #include <nvhe/mem_protect.h>
 #include <nvhe/mm.h>
 #include <nvhe/pkvm.h>
+#include <nvhe/trace.h>
 #include <nvhe/trap_handler.h>
 
 DEFINE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
@@ -570,6 +571,35 @@ static void handle___pkvm_teardown_vm(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) = __pkvm_teardown_vm(handle);
 }
 
+static void handle___pkvm_load_tracing(struct kvm_cpu_context *host_ctxt)
+{
+	 DECLARE_REG(unsigned long, desc_hva, host_ctxt, 1);
+	 DECLARE_REG(size_t, desc_size, host_ctxt, 2);
+
+	 cpu_reg(host_ctxt, 1) = __pkvm_load_tracing(desc_hva, desc_size);
+}
+
+static void handle___pkvm_unload_tracing(struct kvm_cpu_context *host_ctxt)
+{
+	__pkvm_unload_tracing();
+
+	cpu_reg(host_ctxt, 1) = 0;
+}
+
+static void handle___pkvm_enable_tracing(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(bool, enable, host_ctxt, 1);
+
+	cpu_reg(host_ctxt, 1) = __pkvm_enable_tracing(enable);
+}
+
+static void handle___pkvm_swap_reader_tracing(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(unsigned int, cpu, host_ctxt, 1);
+
+	cpu_reg(host_ctxt, 1) = __pkvm_swap_reader_tracing(cpu);
+}
+
 typedef void (*hcall_t)(struct kvm_cpu_context *);
 
 #define HANDLE_FUNC(x)	[__KVM_HOST_SMCCC_FUNC_##x] = (hcall_t)handle_##x
@@ -609,6 +639,10 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_vcpu_load),
 	HANDLE_FUNC(__pkvm_vcpu_put),
 	HANDLE_FUNC(__pkvm_tlb_flush_vmid),
+	HANDLE_FUNC(__pkvm_load_tracing),
+	HANDLE_FUNC(__pkvm_unload_tracing),
+	HANDLE_FUNC(__pkvm_enable_tracing),
+	HANDLE_FUNC(__pkvm_swap_reader_tracing),
 };
 
 static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
new file mode 100644
index 000000000000..f9949b243844
--- /dev/null
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -0,0 +1,251 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <nvhe/clock.h>
+#include <nvhe/mem_protect.h>
+#include <nvhe/mm.h>
+#include <nvhe/trace.h>
+
+#include <asm/percpu.h>
+#include <asm/kvm_mmu.h>
+#include <asm/local.h>
+
+#include <linux/simple_ring_buffer.h>
+
+DEFINE_PER_CPU(struct simple_rb_per_cpu, __simple_rbs);
+
+static struct hyp_trace_buffer {
+	struct simple_rb_per_cpu		*simple_rbs;
+	unsigned long				bpages_backing_start;
+	size_t					bpages_backing_size;
+	hyp_spinlock_t				lock;
+} trace_buffer = {
+	.simple_rbs = &__simple_rbs,
+	.lock = __HYP_SPIN_LOCK_UNLOCKED,
+};
+
+static bool hyp_trace_buffer_loaded(struct hyp_trace_buffer *trace_buffer)
+{
+	return trace_buffer->bpages_backing_size > 0;
+}
+
+void *tracing_reserve_entry(unsigned long length)
+{
+	return simple_ring_buffer_reserve(this_cpu_ptr(trace_buffer.simple_rbs), length,
+					  trace_clock());
+}
+
+void tracing_commit_entry(void)
+{
+	simple_ring_buffer_commit(this_cpu_ptr(trace_buffer.simple_rbs));
+}
+
+static int hyp_trace_buffer_load_bpage_backing(struct hyp_trace_buffer *trace_buffer,
+					       struct hyp_trace_desc *desc)
+{
+	unsigned long start = kern_hyp_va(desc->bpages_backing_start);
+	size_t size = desc->bpages_backing_size;
+	int ret;
+
+	if (!PAGE_ALIGNED(start) || !PAGE_ALIGNED(size))
+		return -EINVAL;
+
+	ret = __pkvm_host_donate_hyp(hyp_virt_to_pfn((void *)start), size >> PAGE_SHIFT);
+	if (ret)
+		return ret;
+
+	memset((void *)start, 0, size);
+
+	trace_buffer->bpages_backing_start = start;
+	trace_buffer->bpages_backing_size = size;
+
+	return 0;
+}
+
+static void hyp_trace_buffer_unload_bpage_backing(struct hyp_trace_buffer *trace_buffer)
+{
+	unsigned long start = trace_buffer->bpages_backing_start;
+	size_t size = trace_buffer->bpages_backing_size;
+
+	if (!size)
+		return;
+
+	memset((void *)start, 0, size);
+
+	WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(start), size >> PAGE_SHIFT));
+
+	trace_buffer->bpages_backing_start = 0;
+	trace_buffer->bpages_backing_size = 0;
+}
+
+static void *__pin_shared_page(unsigned long kern_va)
+{
+	void *va = kern_hyp_va((void *)kern_va);
+
+	return hyp_pin_shared_mem(va, va + PAGE_SIZE) ? NULL : va;
+}
+
+static void __unpin_shared_page(void *va)
+{
+	hyp_unpin_shared_mem(va, va + PAGE_SIZE);
+}
+
+static void hyp_trace_buffer_unload(struct hyp_trace_buffer *trace_buffer)
+{
+	int cpu;
+
+	hyp_assert_lock_held(&trace_buffer->lock);
+
+	if (!hyp_trace_buffer_loaded(trace_buffer))
+		return;
+
+	for (cpu = 0; cpu < hyp_nr_cpus; cpu++)
+		__simple_ring_buffer_unload(per_cpu_ptr(trace_buffer->simple_rbs, cpu),
+					    __unpin_shared_page);
+
+	hyp_trace_buffer_unload_bpage_backing(trace_buffer);
+}
+
+static int hyp_trace_buffer_load(struct hyp_trace_buffer *trace_buffer,
+				 struct hyp_trace_desc *desc)
+{
+	struct simple_buffer_page *bpages;
+	struct ring_buffer_desc *rb_desc;
+	int ret, cpu;
+
+	hyp_assert_lock_held(&trace_buffer->lock);
+
+	if (hyp_trace_buffer_loaded(trace_buffer))
+		return -EINVAL;
+
+	ret = hyp_trace_buffer_load_bpage_backing(trace_buffer, desc);
+	if (ret)
+		return ret;
+
+	bpages = (struct simple_buffer_page *)trace_buffer->bpages_backing_start;
+	for_each_ring_buffer_desc(rb_desc, cpu, &desc->trace_buffer_desc) {
+		ret = __simple_ring_buffer_init(per_cpu_ptr(trace_buffer->simple_rbs, cpu),
+						bpages, rb_desc, __pin_shared_page,
+						__unpin_shared_page);
+		if (ret)
+			break;
+
+		bpages += rb_desc->nr_page_va;
+	}
+
+	if (ret)
+		hyp_trace_buffer_unload(trace_buffer);
+
+	return ret;
+}
+
+static bool hyp_trace_desc_validate(struct hyp_trace_desc *desc, size_t desc_size)
+{
+	struct simple_buffer_page *bpages = (struct simple_buffer_page *)desc->bpages_backing_start;
+	struct ring_buffer_desc *rb_desc;
+	void *bpages_end, *desc_end;
+	int cpu;
+
+	desc_end = (void *)desc + desc_size;
+	bpages_end = (void *)desc->bpages_backing_start + desc->bpages_backing_size;
+
+	for_each_ring_buffer_desc(rb_desc, cpu, &desc->trace_buffer_desc) {
+		/* Can we read nr_page_va? */
+		if ((void *)(&rb_desc->nr_page_va + sizeof(rb_desc->nr_page_va)) > desc_end)
+			return false;
+
+		/* Overflow desc? */
+		if ((void *)(rb_desc->page_va + rb_desc->nr_page_va + 1) > desc_end)
+			return false;
+
+		/* Overflow bpages backing memory? */
+		if ((void *)(bpages + rb_desc->nr_page_va + 1) > bpages_end)
+			return false;
+
+		if (cpu >= hyp_nr_cpus)
+			return false;
+
+		bpages += rb_desc->nr_page_va;
+	}
+
+	return true;
+}
+
+int __pkvm_load_tracing(unsigned long desc_hva, size_t desc_size)
+{
+	struct hyp_trace_desc *desc = (struct hyp_trace_desc *)kern_hyp_va(desc_hva);
+	int ret;
+
+	if (!desc_size || !PAGE_ALIGNED(desc_hva) || !PAGE_ALIGNED(desc_size))
+		return -EINVAL;
+
+	ret = __pkvm_host_donate_hyp(hyp_virt_to_pfn((void *)desc),
+				     desc_size >> PAGE_SHIFT);
+	if (ret)
+		return ret;
+
+	if (!hyp_trace_desc_validate(desc, desc_size))
+		goto err_donate_desc;
+
+	hyp_spin_lock(&trace_buffer.lock);
+
+	ret = hyp_trace_buffer_load(&trace_buffer, desc);
+
+	hyp_spin_unlock(&trace_buffer.lock);
+
+err_donate_desc:
+	WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn((void *)desc),
+				       desc_size >> PAGE_SHIFT));
+	return ret;
+}
+
+void __pkvm_unload_tracing(void)
+{
+	hyp_spin_lock(&trace_buffer.lock);
+	hyp_trace_buffer_unload(&trace_buffer);
+	hyp_spin_unlock(&trace_buffer.lock);
+}
+
+int __pkvm_enable_tracing(bool enable)
+{
+	int cpu, ret = enable ? -EINVAL : 0;
+
+	hyp_spin_lock(&trace_buffer.lock);
+
+	if (!hyp_trace_buffer_loaded(&trace_buffer))
+		goto unlock;
+
+	for (cpu = 0; cpu < hyp_nr_cpus; cpu++)
+		simple_ring_buffer_enable_tracing(per_cpu_ptr(trace_buffer.simple_rbs, cpu),
+						  enable);
+
+	ret = 0;
+
+unlock:
+	hyp_spin_unlock(&trace_buffer.lock);
+
+	return ret;
+}
+
+int __pkvm_swap_reader_tracing(unsigned int cpu)
+{
+	int ret;
+
+	if (cpu >= hyp_nr_cpus)
+		return -EINVAL;
+
+	hyp_spin_lock(&trace_buffer.lock);
+
+	if (hyp_trace_buffer_loaded(&trace_buffer))
+		ret = simple_ring_buffer_swap_reader_page(
+				per_cpu_ptr(trace_buffer.simple_rbs, cpu));
+	else
+		ret = -ENODEV;
+
+	hyp_spin_unlock(&trace_buffer.lock);
+
+	return ret;
+}
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 18/24] KVM: arm64: Add trace remote for the pKVM hyp

[Vincent Donnefort]

When running with KVM protected mode, the hypervisor is able to generate
events into tracefs compatible ring-buffers. Create a trace remote so
the kernel can read those buffers.

This currently doesn't provide any event support which will come later.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index f65eba00c1c9..f7d1d8987cce 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -87,6 +87,7 @@ config PKVM_TRACING
 	bool
 	depends on KVM
 	depends on TRACING
+	select TRACE_REMOTE
 	select SIMPLE_RING_BUFFER
 	default y
 
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 209bc76263f1..fffbbc172bcc 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -29,6 +29,8 @@ kvm-$(CONFIG_HW_PERF_EVENTS)  += pmu-emul.o pmu.o
 kvm-$(CONFIG_ARM64_PTR_AUTH)  += pauth.o
 kvm-$(CONFIG_PTDUMP_STAGE2_DEBUGFS) += ptdump.o
 
+kvm-$(CONFIG_PKVM_TRACING) += hyp_trace.o
+
 always-y := hyp_constants.h hyp-constants.s
 
 define rule_gen_hyp_constants
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 58e8119f66bd..bb800cf55cfd 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -25,6 +25,7 @@
 
 #define CREATE_TRACE_POINTS
 #include "trace_arm.h"
+#include "hyp_trace.h"
 
 #include <linux/uaccess.h>
 #include <asm/ptrace.h>
@@ -2355,6 +2356,9 @@ static int __init init_subsystems(void)
 
 	kvm_register_perf_callbacks(NULL);
 
+	err = hyp_trace_init();
+	if (err)
+		kvm_err("Failed to initialize Hyp tracing\n");
 out:
 	if (err)
 		hyp_cpu_pm_exit();
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
new file mode 100644
index 000000000000..6a2f02cd6c7f
--- /dev/null
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -0,0 +1,209 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <linux/trace_remote.h>
+#include <linux/simple_ring_buffer.h>
+
+#include <asm/kvm_host.h>
+#include <asm/kvm_hyptrace.h>
+
+#include "hyp_trace.h"
+
+/* Access to this struct within the trace_remote_callbacks are protected by the trace_remote lock */
+struct hyp_trace_buffer {
+	struct hyp_trace_desc	*desc;
+	size_t			desc_size;
+} trace_buffer;
+
+static int hyp_trace_buffer_alloc_bpages_backing(struct hyp_trace_buffer *trace_buffer, size_t size)
+{
+	int nr_bpages = (PAGE_ALIGN(size) / PAGE_SIZE) + 1;
+	size_t backing_size;
+	void *start;
+
+	backing_size = PAGE_ALIGN(sizeof(struct simple_buffer_page) * nr_bpages *
+				  num_possible_cpus());
+
+	start = alloc_pages_exact(backing_size, GFP_KERNEL_ACCOUNT);
+	if (!start)
+		return -ENOMEM;
+
+	trace_buffer->desc->bpages_backing_start = (unsigned long)start;
+	trace_buffer->desc->bpages_backing_size = backing_size;
+
+	return 0;
+}
+
+static void hyp_trace_buffer_free_bpages_backing(struct hyp_trace_buffer *trace_buffer)
+{
+	free_pages_exact((void *)trace_buffer->desc->bpages_backing_start,
+			 trace_buffer->desc->bpages_backing_size);
+}
+
+static int __load_page(unsigned long va)
+{
+	return kvm_call_hyp_nvhe(__pkvm_host_share_hyp, virt_to_pfn((void *)va), 1);
+}
+
+static void __unload_page(unsigned long va)
+{
+	WARN_ON(kvm_call_hyp_nvhe(__pkvm_host_unshare_hyp, virt_to_pfn((void *)va), 1));
+}
+
+static void hyp_trace_buffer_unload_pages(struct hyp_trace_buffer *trace_buffer, int last_cpu)
+{
+	struct ring_buffer_desc *rb_desc;
+	int cpu, p;
+
+	for_each_ring_buffer_desc(rb_desc, cpu, &trace_buffer->desc->trace_buffer_desc) {
+		if (cpu > last_cpu)
+			break;
+
+		__unload_page(rb_desc->meta_va);
+		for (p = 0; p < rb_desc->nr_page_va; p++)
+			__unload_page(rb_desc->page_va[p]);
+	}
+}
+
+static int hyp_trace_buffer_load_pages(struct hyp_trace_buffer *trace_buffer)
+{
+	struct ring_buffer_desc *rb_desc;
+	int cpu, p, ret = 0;
+
+	for_each_ring_buffer_desc(rb_desc, cpu, &trace_buffer->desc->trace_buffer_desc) {
+		ret = __load_page(rb_desc->meta_va);
+		if (ret)
+			break;
+
+		for (p = 0; p < rb_desc->nr_page_va; p++) {
+			ret = __load_page(rb_desc->page_va[p]);
+			if (ret)
+				break;
+		}
+
+		if (ret) {
+			for (p--; p >= 0; p--)
+				__unload_page(rb_desc->page_va[p]);
+			break;
+		}
+	}
+
+	if (ret)
+		hyp_trace_buffer_unload_pages(trace_buffer, cpu--);
+
+	return ret;
+}
+
+static struct trace_buffer_desc *hyp_trace_load(unsigned long size, void *priv)
+{
+	struct hyp_trace_buffer *trace_buffer = priv;
+	struct hyp_trace_desc *desc;
+	size_t desc_size;
+	int ret;
+
+	if (WARN_ON(trace_buffer->desc))
+		return NULL;
+
+	desc_size = trace_buffer_desc_size(size, num_possible_cpus());
+	if (desc_size == SIZE_MAX)
+		return NULL;
+
+	/*
+	 * The hypervisor will unmap the descriptor from the host to protect the reading. Page
+	 * granularity for the allocation ensures no other useful data will be unmapped.
+	 */
+	desc_size = PAGE_ALIGN(desc_size);
+	desc = (struct hyp_trace_desc *)alloc_pages_exact(desc_size, GFP_KERNEL);
+	if (!desc)
+		return NULL;
+
+	trace_buffer->desc = desc;
+
+	ret = hyp_trace_buffer_alloc_bpages_backing(trace_buffer, size);
+	if (ret)
+		goto err_free_desc;
+
+	ret = trace_remote_alloc_buffer(&desc->trace_buffer_desc, size, cpu_possible_mask);
+	if (ret)
+		goto err_free_backing;
+
+	ret = hyp_trace_buffer_load_pages(trace_buffer);
+	if (ret)
+		goto err_free_buffer;
+
+	ret = kvm_call_hyp_nvhe(__pkvm_load_tracing, (unsigned long)desc, desc_size);
+	if (ret)
+		goto err_unload_pages;
+
+	return &desc->trace_buffer_desc;
+
+err_unload_pages:
+	hyp_trace_buffer_unload_pages(trace_buffer, INT_MAX);
+
+err_free_buffer:
+	trace_remote_free_buffer(&desc->trace_buffer_desc);
+
+err_free_backing:
+	hyp_trace_buffer_free_bpages_backing(trace_buffer);
+
+err_free_desc:
+	free_pages_exact(desc, desc_size);
+	trace_buffer->desc = NULL;
+
+	return NULL;
+}
+
+static void hyp_trace_unload(struct trace_buffer_desc *desc, void *priv)
+{
+	struct hyp_trace_buffer *trace_buffer = priv;
+
+	if (WARN_ON(desc != &trace_buffer->desc->trace_buffer_desc))
+		return;
+
+	kvm_call_hyp_nvhe(__pkvm_unload_tracing);
+	hyp_trace_buffer_unload_pages(trace_buffer, INT_MAX);
+	trace_remote_free_buffer(desc);
+	hyp_trace_buffer_free_bpages_backing(trace_buffer);
+	free_pages_exact(trace_buffer->desc, trace_buffer->desc_size);
+	trace_buffer->desc = NULL;
+}
+
+static int hyp_trace_enable_tracing(bool enable, void *priv)
+{
+	return kvm_call_hyp_nvhe(__pkvm_enable_tracing, enable);
+}
+
+static int hyp_trace_swap_reader_page(unsigned int cpu, void *priv)
+{
+	return kvm_call_hyp_nvhe(__pkvm_swap_reader_tracing, cpu);
+}
+
+static int hyp_trace_reset(unsigned int cpu, void *priv)
+{
+	return 0;
+}
+
+static int hyp_trace_enable_event(unsigned short id, bool enable, void *priv)
+{
+	return 0;
+}
+
+static struct trace_remote_callbacks trace_remote_callbacks = {
+	.load_trace_buffer	= hyp_trace_load,
+	.unload_trace_buffer	= hyp_trace_unload,
+	.enable_tracing		= hyp_trace_enable_tracing,
+	.swap_reader_page	= hyp_trace_swap_reader_page,
+	.reset			= hyp_trace_reset,
+	.enable_event		= hyp_trace_enable_event,
+};
+
+int hyp_trace_init(void)
+{
+	if (!is_protected_kvm_enabled())
+		return 0;
+
+	return trace_remote_register("hypervisor", &trace_remote_callbacks, &trace_buffer, NULL, 0);
+}
diff --git a/arch/arm64/kvm/hyp_trace.h b/arch/arm64/kvm/hyp_trace.h
new file mode 100644
index 000000000000..54d8b1f44ca5
--- /dev/null
+++ b/arch/arm64/kvm/hyp_trace.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ARM64_KVM_HYP_TRACE_H__
+#define __ARM64_KVM_HYP_TRACE_H__
+
+#ifdef CONFIG_PKVM_TRACING
+int hyp_trace_init(void);
+#else
+static inline int hyp_trace_init(void) { return 0; }
+#endif
+#endif
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 19/24] KVM: arm64: Sync boot clock with the pKVM hyp

[Vincent Donnefort]

Configure the pKVM hypervisor tracing clock with the kernel boot clock.
For tracing purpose, the boot clock is interesting as it doesn't stop on
suspend. However, it is corrected on a regular basis, which implies we
need to re-evaluate it every once in a while.

Cc: John Stultz <jstultz@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Christopher S. Hall <christopher.s.hall@intel.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 437ac948d136..d122d79718a0 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -87,6 +87,7 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_load,
 	__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_put,
 	__KVM_HOST_SMCCC_FUNC___pkvm_tlb_flush_vmid,
+	__KVM_HOST_SMCCC_FUNC___pkvm_update_clock_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_load_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_unload_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_enable_tracing,
diff --git a/arch/arm64/kvm/hyp/include/nvhe/trace.h b/arch/arm64/kvm/hyp/include/nvhe/trace.h
index 996e90c0974f..4e11dcdf049b 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/trace.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/trace.h
@@ -7,6 +7,7 @@
 void *tracing_reserve_entry(unsigned long length);
 void tracing_commit_entry(void);
 
+void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc);
 int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size);
 void __pkvm_unload_tracing(void);
 int __pkvm_enable_tracing(bool enable);
@@ -15,6 +16,8 @@ int __pkvm_swap_reader_tracing(unsigned int cpu);
 static inline void *tracing_reserve_entry(unsigned long length) { return NULL; }
 static inline void tracing_commit_entry(void) { }
 
+static inline
+void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc) { }
 static inline int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size) { return -ENODEV; }
 static inline void __pkvm_unload_tracing(void) { }
 static inline int __pkvm_enable_tracing(bool enable) { return -ENODEV; }
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 68b98547666b..c73229fb5e1b 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -571,6 +571,18 @@ static void handle___pkvm_teardown_vm(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) = __pkvm_teardown_vm(handle);
 }
 
+static void handle___pkvm_update_clock_tracing(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(u32, mult, host_ctxt, 1);
+	DECLARE_REG(u32, shift, host_ctxt, 2);
+	DECLARE_REG(u64, epoch_ns, host_ctxt, 3);
+	DECLARE_REG(u64, epoch_cyc, host_ctxt, 4);
+
+	__pkvm_update_clock_tracing(mult, shift, epoch_ns, epoch_cyc);
+
+	cpu_reg(host_ctxt, 1) = 0;
+}
+
 static void handle___pkvm_load_tracing(struct kvm_cpu_context *host_ctxt)
 {
 	 DECLARE_REG(unsigned long, desc_hva, host_ctxt, 1);
@@ -639,6 +651,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_vcpu_load),
 	HANDLE_FUNC(__pkvm_vcpu_put),
 	HANDLE_FUNC(__pkvm_tlb_flush_vmid),
+	HANDLE_FUNC(__pkvm_update_clock_tracing),
 	HANDLE_FUNC(__pkvm_load_tracing),
 	HANDLE_FUNC(__pkvm_unload_tracing),
 	HANDLE_FUNC(__pkvm_enable_tracing),
diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
index f9949b243844..32fd889315f0 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -249,3 +249,19 @@ int __pkvm_swap_reader_tracing(unsigned int cpu)
 
 	return ret;
 }
+
+void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
+{
+	int cpu;
+
+	/* After this loop, all CPUs are observing the new bank... */
+	for (cpu = 0; cpu < hyp_nr_cpus; cpu++) {
+		struct simple_rb_per_cpu *simple_rb = per_cpu_ptr(trace_buffer.simple_rbs, cpu);
+
+		while (READ_ONCE(simple_rb->status) == SIMPLE_RB_WRITING)
+			;
+	}
+
+	/* ...we can now override the old one and swap. */
+	trace_clock_update(mult, shift, epoch_ns, epoch_cyc);
+}
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 6a2f02cd6c7f..516d6c63c145 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/trace_remote.h>
+#include <linux/tracefs.h>
 #include <linux/simple_ring_buffer.h>
 
 #include <asm/kvm_host.h>
@@ -12,6 +13,121 @@
 
 #include "hyp_trace.h"
 
+/* Same 10min used by clocksource when width is more than 32-bits */
+#define CLOCK_MAX_CONVERSION_S	600
+/*
+ * Time to give for the clock init. Long enough to get a good mult/shift
+ * estimation. Short enough to not delay the tracing start too much.
+ */
+#define CLOCK_INIT_MS		100
+/*
+ * Time between clock checks. Must be small enough to catch clock deviation when
+ * it is still tiny.
+ */
+#define CLOCK_UPDATE_MS		500
+
+static struct hyp_trace_clock {
+	u64			cycles;
+	u64			cyc_overflow64;
+	u64			boot;
+	u32			mult;
+	u32			shift;
+	struct delayed_work	work;
+	struct completion	ready;
+	struct mutex		lock;
+	bool			running;
+} hyp_clock;
+
+static void __hyp_clock_work(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct hyp_trace_clock *hyp_clock;
+	struct system_time_snapshot snap;
+	u64 rate, delta_cycles;
+	u64 boot, delta_boot;
+
+	hyp_clock = container_of(dwork, struct hyp_trace_clock, work);
+
+	ktime_get_snapshot(&snap);
+	boot = ktime_to_ns(snap.boot);
+
+	delta_boot = boot - hyp_clock->boot;
+	delta_cycles = snap.cycles - hyp_clock->cycles;
+
+	/* Compare hyp clock with the kernel boot clock */
+	if (hyp_clock->mult) {
+		u64 err, cur = delta_cycles;
+
+		if (WARN_ON_ONCE(cur >= hyp_clock->cyc_overflow64)) {
+			__uint128_t tmp = (__uint128_t)cur * hyp_clock->mult;
+
+			cur = tmp >> hyp_clock->shift;
+		} else {
+			cur *= hyp_clock->mult;
+			cur >>= hyp_clock->shift;
+		}
+		cur += hyp_clock->boot;
+
+		err = abs_diff(cur, boot);
+		/* No deviation, only update epoch if necessary */
+		if (!err) {
+			if (delta_cycles >= (hyp_clock->cyc_overflow64 >> 1))
+				goto fast_forward;
+
+			goto resched;
+		}
+
+		/* Warn if the error is above tracing precision (1us) */
+		if (err > NSEC_PER_USEC)
+			pr_warn_ratelimited("hyp trace clock off by %lluus\n",
+					    err / NSEC_PER_USEC);
+	}
+
+	rate = div64_u64(delta_cycles * NSEC_PER_SEC, delta_boot);
+
+	clocks_calc_mult_shift(&hyp_clock->mult, &hyp_clock->shift,
+			       rate, NSEC_PER_SEC, CLOCK_MAX_CONVERSION_S);
+
+	/* Add a comfortable 50% margin */
+	hyp_clock->cyc_overflow64 = (U64_MAX / hyp_clock->mult) >> 1;
+
+fast_forward:
+	hyp_clock->cycles = snap.cycles;
+	hyp_clock->boot = boot;
+	kvm_call_hyp_nvhe(__pkvm_update_clock_tracing, hyp_clock->mult,
+			  hyp_clock->shift, hyp_clock->boot, hyp_clock->cycles);
+	complete(&hyp_clock->ready);
+
+resched:
+	schedule_delayed_work(&hyp_clock->work,
+			      msecs_to_jiffies(CLOCK_UPDATE_MS));
+}
+
+static void hyp_trace_clock_enable(struct hyp_trace_clock *hyp_clock, bool enable)
+{
+	struct system_time_snapshot snap;
+
+	if (hyp_clock->running == enable)
+		return;
+
+	if (!enable) {
+		cancel_delayed_work_sync(&hyp_clock->work);
+		hyp_clock->running = false;
+	}
+
+	ktime_get_snapshot(&snap);
+
+	hyp_clock->boot = ktime_to_ns(snap.boot);
+	hyp_clock->cycles = snap.cycles;
+	hyp_clock->mult = 0;
+
+	init_completion(&hyp_clock->ready);
+	INIT_DELAYED_WORK(&hyp_clock->work, __hyp_clock_work);
+	schedule_delayed_work(&hyp_clock->work, msecs_to_jiffies(CLOCK_INIT_MS));
+	wait_for_completion(&hyp_clock->ready);
+	hyp_clock->running = true;
+}
+
 /* Access to this struct within the trace_remote_callbacks are protected by the trace_remote lock */
 struct hyp_trace_buffer {
 	struct hyp_trace_desc	*desc;
@@ -173,6 +289,8 @@ static void hyp_trace_unload(struct trace_buffer_desc *desc, void *priv)
 
 static int hyp_trace_enable_tracing(bool enable, void *priv)
 {
+	hyp_trace_clock_enable(&hyp_clock, enable);
+
 	return kvm_call_hyp_nvhe(__pkvm_enable_tracing, enable);
 }
 
@@ -191,7 +309,22 @@ static int hyp_trace_enable_event(unsigned short id, bool enable, void *priv)
 	return 0;
 }
 
+static int hyp_trace_clock_show(struct seq_file *m, void *v)
+{
+	seq_puts(m, "[boot]\n");
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(hyp_trace_clock);
+
+static int hyp_trace_init_tracefs(struct dentry *d, void *priv)
+{
+	return tracefs_create_file("trace_clock", 0440, d, NULL, &hyp_trace_clock_fops) ?
+		0 : -ENOMEM;
+}
+
 static struct trace_remote_callbacks trace_remote_callbacks = {
+	.init			= hyp_trace_init_tracefs,
 	.load_trace_buffer	= hyp_trace_load,
 	.unload_trace_buffer	= hyp_trace_unload,
 	.enable_tracing		= hyp_trace_enable_tracing,
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 20/24] KVM: arm64: Add trace reset to the pKVM hyp

[Vincent Donnefort]

Let the hypervisor reset the trace buffer when triggered from the
tracefs file remotes/hypervisor/trace.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index d122d79718a0..c40820a4b049 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -91,6 +91,7 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_load_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_unload_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_enable_tracing,
+	__KVM_HOST_SMCCC_FUNC___pkvm_reset_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_swap_reader_tracing,
 };
 
diff --git a/arch/arm64/kvm/hyp/include/nvhe/trace.h b/arch/arm64/kvm/hyp/include/nvhe/trace.h
index 4e11dcdf049b..0d2732f0d406 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/trace.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/trace.h
@@ -11,6 +11,7 @@ void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cy
 int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size);
 void __pkvm_unload_tracing(void);
 int __pkvm_enable_tracing(bool enable);
+int __pkvm_reset_tracing(unsigned int cpu);
 int __pkvm_swap_reader_tracing(unsigned int cpu);
 #else
 static inline void *tracing_reserve_entry(unsigned long length) { return NULL; }
@@ -21,6 +22,7 @@ void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cy
 static inline int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size) { return -ENODEV; }
 static inline void __pkvm_unload_tracing(void) { }
 static inline int __pkvm_enable_tracing(bool enable) { return -ENODEV; }
+static inline int __pkvm_reset_tracing(unsigned int cpu) { return -ENODEV; }
 static inline int __pkvm_swap_reader_tracing(unsigned int cpu) { return -ENODEV; }
 #endif
 #endif
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index c73229fb5e1b..65260bfd33ac 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -605,6 +605,13 @@ static void handle___pkvm_enable_tracing(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) = __pkvm_enable_tracing(enable);
 }
 
+static void handle___pkvm_reset_tracing(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(unsigned int, cpu, host_ctxt, 1);
+
+	cpu_reg(host_ctxt, 1) = __pkvm_reset_tracing(cpu);
+}
+
 static void handle___pkvm_swap_reader_tracing(struct kvm_cpu_context *host_ctxt)
 {
 	DECLARE_REG(unsigned int, cpu, host_ctxt, 1);
@@ -655,6 +662,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_load_tracing),
 	HANDLE_FUNC(__pkvm_unload_tracing),
 	HANDLE_FUNC(__pkvm_enable_tracing),
+	HANDLE_FUNC(__pkvm_reset_tracing),
 	HANDLE_FUNC(__pkvm_swap_reader_tracing),
 };
 
diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
index 32fd889315f0..b6d97237a7a0 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -230,6 +230,25 @@ int __pkvm_enable_tracing(bool enable)
 	return ret;
 }
 
+int __pkvm_reset_tracing(unsigned int cpu)
+{
+	int ret = 0;
+
+	if (cpu >= hyp_nr_cpus)
+		return -EINVAL;
+
+	hyp_spin_lock(&trace_buffer.lock);
+
+	if (hyp_trace_buffer_loaded(&trace_buffer))
+		ret = simple_ring_buffer_reset(per_cpu_ptr(trace_buffer.simple_rbs, cpu));
+	else
+		ret = -ENODEV;
+
+	hyp_spin_unlock(&trace_buffer.lock);
+
+	return ret;
+}
+
 int __pkvm_swap_reader_tracing(unsigned int cpu)
 {
 	int ret;
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 516d6c63c145..c7ad36212a7d 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -301,7 +301,7 @@ static int hyp_trace_swap_reader_page(unsigned int cpu, void *priv)
 
 static int hyp_trace_reset(unsigned int cpu, void *priv)
 {
-	return 0;
+	return kvm_call_hyp_nvhe(__pkvm_reset_tracing, cpu);
 }
 
 static int hyp_trace_enable_event(unsigned short id, bool enable, void *priv)
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 21/24] KVM: arm64: Add event support to the pKVM hyp and trace remote

[Vincent Donnefort]

Allow the creation of hypervisor and trace remote events with a single
macro HYP_EVENT(). That macro expands in the kernel side to add all
the required declarations (based on REMOTE_EVENT()) as well as in the
hypervisor side to create the trace_<event>() function.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index c40820a4b049..79019e11f529 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -93,6 +93,7 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_enable_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_reset_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_swap_reader_tracing,
+	__KVM_HOST_SMCCC_FUNC___pkvm_enable_event,
 };
 
 #define DECLARE_KVM_VHE_SYM(sym)	extern char sym[]
diff --git a/arch/arm64/include/asm/kvm_define_hypevents.h b/arch/arm64/include/asm/kvm_define_hypevents.h
new file mode 100644
index 000000000000..0ef5a9eefcbe
--- /dev/null
+++ b/arch/arm64/include/asm/kvm_define_hypevents.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef HYP_EVENT_FILE
+# undef __ARM64_KVM_HYPEVENTS_H_
+# define REMOTE_EVENT_INCLUDE_FILE arch/arm64/include/asm/kvm_hypevents.h
+#else
+# define REMOTE_EVENT_INCLUDE_FILE HYP_EVENT_FILE
+#endif
+
+#define REMOTE_EVENT_SECTION "_hyp_events"
+
+#define HE_STRUCT(__args)		__args
+#define HE_PRINTK(__args...)		__args
+#define he_field			re_field
+
+#define HYP_EVENT(__name, __proto, __struct, __assign, __printk) \
+	REMOTE_EVENT(__name, 0, RE_STRUCT(__struct), RE_PRINTK(__printk))
+
+#define HYP_EVENT_MULTI_READ
+
+#include <trace/define_remote_events.h>
diff --git a/arch/arm64/include/asm/kvm_hypevents.h b/arch/arm64/include/asm/kvm_hypevents.h
new file mode 100644
index 000000000000..d6e033c96c52
--- /dev/null
+++ b/arch/arm64/include/asm/kvm_hypevents.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#if !defined(__ARM64_KVM_HYPEVENTS_H_) || defined(HYP_EVENT_MULTI_READ)
+#define __ARM64_KVM_HYPEVENTS_H_
+
+#ifdef __KVM_NVHE_HYPERVISOR__
+#include <nvhe/trace.h>
+#endif
+
+#endif
diff --git a/arch/arm64/include/asm/kvm_hyptrace.h b/arch/arm64/include/asm/kvm_hyptrace.h
index 9c30a479bc36..d6e0953a07d6 100644
--- a/arch/arm64/include/asm/kvm_hyptrace.h
+++ b/arch/arm64/include/asm/kvm_hyptrace.h
@@ -10,4 +10,17 @@ struct hyp_trace_desc {
 	struct trace_buffer_desc	trace_buffer_desc;
 
 };
+
+struct hyp_event_id {
+	unsigned short	id;
+	void		*data;
+};
+
+extern struct remote_event __hyp_events_start[];
+extern struct remote_event __hyp_events_end[];
+
+/* hyp_event section used by the hypervisor */
+extern struct hyp_event_id __hyp_event_ids_start[];
+extern struct hyp_event_id __hyp_event_ids_end[];
+
 #endif
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index 9c5345f1ab66..7466630ecb10 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -135,6 +135,10 @@ KVM_NVHE_ALIAS(__hyp_data_start);
 KVM_NVHE_ALIAS(__hyp_data_end);
 KVM_NVHE_ALIAS(__hyp_rodata_start);
 KVM_NVHE_ALIAS(__hyp_rodata_end);
+#ifdef CONFIG_PKVM_TRACING
+KVM_NVHE_ALIAS(__hyp_event_ids_start);
+KVM_NVHE_ALIAS(__hyp_event_ids_end);
+#endif
 
 /* pKVM static key */
 KVM_NVHE_ALIAS(kvm_protected_mode_initialized);
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 7c770053f072..c9baff9d6f3a 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -13,12 +13,23 @@
 	*(__kvm_ex_table)					\
 	__stop___kvm_ex_table = .;
 
+#ifdef CONFIG_PKVM_TRACING
+#define HYPERVISOR_EVENT_IDS 					\
+	. = ALIGN(PAGE_SIZE);					\
+	__hyp_event_ids_start = .;				\
+	*(HYP_SECTION_NAME(.event_ids))				\
+	__hyp_event_ids_end = .;
+#else
+#define HYPERVISOR_EVENT_IDS
+#endif
+
 #define HYPERVISOR_RODATA_SECTIONS				\
 	HYP_SECTION_NAME(.rodata) : {				\
 		. = ALIGN(PAGE_SIZE);				\
 		__hyp_rodata_start = .;				\
 		*(HYP_SECTION_NAME(.data..ro_after_init))	\
 		*(HYP_SECTION_NAME(.rodata))			\
+		HYPERVISOR_EVENT_IDS				\
 		. = ALIGN(PAGE_SIZE);				\
 		__hyp_rodata_end = .;				\
 	}
@@ -307,6 +318,13 @@ SECTIONS
 
 	HYPERVISOR_DATA_SECTION
 
+#ifdef CONFIG_PKVM_TRACING
+	.data.hyp_events : {
+		__hyp_events_start = .;
+		*(SORT(_hyp_events.*))
+		__hyp_events_end = .;
+	}
+#endif
 	/*
 	 * Data written with the MMU off but read with the MMU on requires
 	 * cache lines to be invalidated, discarding up to a Cache Writeback
diff --git a/arch/arm64/kvm/hyp/include/nvhe/define_events.h b/arch/arm64/kvm/hyp/include/nvhe/define_events.h
new file mode 100644
index 000000000000..2298b49cb355
--- /dev/null
+++ b/arch/arm64/kvm/hyp/include/nvhe/define_events.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef HYP_EVENT_FILE
+# define __HYP_EVENT_FILE <asm/kvm_hypevents.h>
+#else
+# define __HYP_EVENT_FILE __stringify(HYP_EVENT_FILE)
+#endif
+
+#undef HYP_EVENT
+#define HYP_EVENT(__name, __proto, __struct, __assign, __printk)	\
+	atomic_t __ro_after_init __name##_enabled = ATOMIC_INIT(0);	\
+	struct hyp_event_id hyp_event_id_##__name			\
+	__section(".hyp.event_ids."#__name) = {				\
+		.data = (void *)&__name##_enabled,			\
+	}
+
+#define HYP_EVENT_MULTI_READ
+#include __HYP_EVENT_FILE
+#undef HYP_EVENT_MULTI_READ
+
+#undef HYP_EVENT
diff --git a/arch/arm64/kvm/hyp/include/nvhe/trace.h b/arch/arm64/kvm/hyp/include/nvhe/trace.h
index 0d2732f0d406..09abbc8113ca 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/trace.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/trace.h
@@ -1,21 +1,51 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 #ifndef __ARM64_KVM_HYP_NVHE_TRACE_H
 #define __ARM64_KVM_HYP_NVHE_TRACE_H
+
+#include <linux/trace_remote_event.h>
+
 #include <asm/kvm_hyptrace.h>
 
 #ifdef CONFIG_PKVM_TRACING
 void *tracing_reserve_entry(unsigned long length);
 void tracing_commit_entry(void);
 
+#define HE_PROTO(__args...)	__args
+#define HE_ASSIGN(__args...)	__args
+#define HE_STRUCT		RE_STRUCT
+#define he_field		re_field
+
+#define HYP_EVENT(__name, __proto, __struct, __assign, __printk)		\
+	REMOTE_EVENT_FORMAT(__name, __struct);					\
+	extern atomic_t __name##_enabled;					\
+	extern struct hyp_event_id hyp_event_id_##__name;			\
+	static __always_inline void trace_##__name(__proto)			\
+	{									\
+		struct remote_event_format_##__name *__entry;			\
+		size_t length = sizeof(*__entry);				\
+										\
+		if (!atomic_read(&__name##_enabled))				\
+			return;							\
+		__entry = tracing_reserve_entry(length);			\
+		if (!__entry)							\
+			return;							\
+		__entry->hdr.id = hyp_event_id_##__name.id;			\
+		__assign							\
+		tracing_commit_entry();						\
+	}
+
 void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc);
 int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size);
 void __pkvm_unload_tracing(void);
 int __pkvm_enable_tracing(bool enable);
 int __pkvm_reset_tracing(unsigned int cpu);
 int __pkvm_swap_reader_tracing(unsigned int cpu);
+int __pkvm_enable_event(unsigned short id, bool enable);
 #else
 static inline void *tracing_reserve_entry(unsigned long length) { return NULL; }
 static inline void tracing_commit_entry(void) { }
+#define HYP_EVENT(__name, __proto, __struct, __assign, __printk)      \
+	static inline void trace_##__name(__proto) {}
 
 static inline
 void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc) { }
@@ -24,5 +54,6 @@ static inline void __pkvm_unload_tracing(void) { }
 static inline int __pkvm_enable_tracing(bool enable) { return -ENODEV; }
 static inline int __pkvm_reset_tracing(unsigned int cpu) { return -ENODEV; }
 static inline int __pkvm_swap_reader_tracing(unsigned int cpu) { return -ENODEV; }
+static inline int __pkvm_enable_event(unsigned short id, bool enable)  { return -ENODEV; }
 #endif
 #endif
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index 6d92f58aea7e..1467c9f28558 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -28,7 +28,7 @@ hyp-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o
 hyp-obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
 	 ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
 hyp-obj-$(CONFIG_LIST_HARDENED) += list_debug.o
-hyp-obj-$(CONFIG_PKVM_TRACING) += clock.o trace.o ../../../../../kernel/trace/simple_ring_buffer.o
+hyp-obj-$(CONFIG_PKVM_TRACING) += clock.o trace.o ../../../../../kernel/trace/simple_ring_buffer.o events.o
 hyp-obj-y += $(lib-objs)
 
 ##
diff --git a/arch/arm64/kvm/hyp/nvhe/events.c b/arch/arm64/kvm/hyp/nvhe/events.c
new file mode 100644
index 000000000000..5905b42cb0d0
--- /dev/null
+++ b/arch/arm64/kvm/hyp/nvhe/events.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <nvhe/mm.h>
+#include <nvhe/trace.h>
+
+#include <nvhe/define_events.h>
+
+extern struct hyp_event_id __hyp_event_ids_start[];
+extern struct hyp_event_id __hyp_event_ids_end[];
+
+int __pkvm_enable_event(unsigned short id, bool enable)
+{
+	struct hyp_event_id *event_id = __hyp_event_ids_start;
+	atomic_t *enable_key;
+
+	for (; (unsigned long)event_id < (unsigned long)__hyp_event_ids_end;
+	     event_id++) {
+		if (event_id->id != id)
+			continue;
+
+		enable_key = (atomic_t *)event_id->data;
+		enable_key = hyp_fixmap_map(__hyp_pa(enable_key));
+
+		atomic_set(enable_key, enable);
+
+		hyp_fixmap_unmap();
+
+		return 0;
+	}
+
+	return -EINVAL;
+}
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 65260bfd33ac..3d36be6d94ca 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -619,6 +619,14 @@ static void handle___pkvm_swap_reader_tracing(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) = __pkvm_swap_reader_tracing(cpu);
 }
 
+static void handle___pkvm_enable_event(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(unsigned short, id, host_ctxt, 1);
+	DECLARE_REG(bool, enable, host_ctxt, 2);
+
+	cpu_reg(host_ctxt, 1) = __pkvm_enable_event(id, enable);
+}
+
 typedef void (*hcall_t)(struct kvm_cpu_context *);
 
 #define HANDLE_FUNC(x)	[__KVM_HOST_SMCCC_FUNC_##x] = (hcall_t)handle_##x
@@ -664,6 +672,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_enable_tracing),
 	HANDLE_FUNC(__pkvm_reset_tracing),
 	HANDLE_FUNC(__pkvm_swap_reader_tracing),
+	HANDLE_FUNC(__pkvm_enable_event),
 };
 
 static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
index d724f6d69302..a68411bf4bef 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
@@ -16,6 +16,12 @@ SECTIONS {
 	HYP_SECTION(.text)
 	HYP_SECTION(.data..ro_after_init)
 	HYP_SECTION(.rodata)
+#ifdef CONFIG_PKVM_TRACING
+	. = ALIGN(PAGE_SIZE);
+	BEGIN_HYP_SECTION(.event_ids)
+		*(SORT(.hyp.event_ids.*))
+	END_HYP_SECTION
+#endif
 
 	/*
 	 * .hyp..data..percpu needs to be page aligned to maintain the same
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index c7ad36212a7d..1a4313362aa0 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -306,7 +306,7 @@ static int hyp_trace_reset(unsigned int cpu, void *priv)
 
 static int hyp_trace_enable_event(unsigned short id, bool enable, void *priv)
 {
-	return 0;
+	return kvm_call_hyp_nvhe(__pkvm_enable_event, id, enable);
 }
 
 static int hyp_trace_clock_show(struct seq_file *m, void *v)
@@ -333,10 +333,27 @@ static struct trace_remote_callbacks trace_remote_callbacks = {
 	.enable_event		= hyp_trace_enable_event,
 };
 
+#include <asm/kvm_define_hypevents.h>
+
+static void hyp_trace_init_events(void)
+{
+	struct hyp_event_id *hyp_event_id = __hyp_event_ids_start;
+	struct remote_event *event = __hyp_events_start;
+	int id = 0;
+
+	/* Events on both sides hypervisor are sorted */
+	for (; (unsigned long)event < (unsigned long)__hyp_events_end;
+		event++, hyp_event_id++, id++)
+		event->id = hyp_event_id->id = id;
+}
+
 int hyp_trace_init(void)
 {
 	if (!is_protected_kvm_enabled())
 		return 0;
 
-	return trace_remote_register("hypervisor", &trace_remote_callbacks, &trace_buffer, NULL, 0);
+	hyp_trace_init_events();
+
+	return trace_remote_register("hypervisor", &trace_remote_callbacks, &trace_buffer,
+				     __hyp_events_start, __hyp_events_end - __hyp_events_start);
 }
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 22/24] KVM: arm64: Add hyp_enter/hyp_exit events to pKVM hyp

[Vincent Donnefort]

The hyp_enter and hyp_exit events are logged by the hypervisor any time
it is entered and exited.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/include/asm/kvm_hypevents.h b/arch/arm64/include/asm/kvm_hypevents.h
index d6e033c96c52..ce3953bc884a 100644
--- a/arch/arm64/include/asm/kvm_hypevents.h
+++ b/arch/arm64/include/asm/kvm_hypevents.h
@@ -7,4 +7,21 @@
 #include <nvhe/trace.h>
 #endif
 
+HYP_EVENT(hyp_enter,
+	HE_PROTO(void),
+	HE_STRUCT(
+	),
+	HE_ASSIGN(
+	),
+	HE_PRINTK()
+);
+
+HYP_EVENT(hyp_exit,
+	HE_PROTO(void),
+	HE_STRUCT(
+	),
+	HE_ASSIGN(
+	),
+	HE_PRINTK()
+);
 #endif
diff --git a/arch/arm64/kvm/hyp/include/nvhe/arm-smccc.h b/arch/arm64/kvm/hyp/include/nvhe/arm-smccc.h
new file mode 100644
index 000000000000..4b69d33e4f2d
--- /dev/null
+++ b/arch/arm64/kvm/hyp/include/nvhe/arm-smccc.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <asm/kvm_hypevents.h>
+
+#include <linux/arm-smccc.h>
+
+#undef arm_smccc_1_1_smc
+#define arm_smccc_1_1_smc(...)					\
+	do {							\
+		trace_hyp_exit();				\
+		__arm_smccc_1_1(SMCCC_SMC_INST, __VA_ARGS__);	\
+		trace_hyp_enter();				\
+	} while (0)
diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 3369dd0c4009..e00931fd194f 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -26,10 +26,10 @@
  * the duration and are therefore serialised.
  */
 
-#include <linux/arm-smccc.h>
 #include <linux/arm_ffa.h>
 #include <asm/kvm_pkvm.h>
 
+#include <nvhe/arm-smccc.h>
 #include <nvhe/ffa.h>
 #include <nvhe/mem_protect.h>
 #include <nvhe/memory.h>
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 3d36be6d94ca..7d7d0c07a6d4 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -12,6 +12,7 @@
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_host.h>
 #include <asm/kvm_hyp.h>
+#include <asm/kvm_hypevents.h>
 #include <asm/kvm_mmu.h>
 
 #include <nvhe/ffa.h>
@@ -713,7 +714,9 @@ static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
 
 static void default_host_smc_handler(struct kvm_cpu_context *host_ctxt)
 {
+	trace_hyp_exit();
 	__kvm_hyp_host_forward_smc(host_ctxt);
+	trace_hyp_enter();
 }
 
 static void handle_host_smc(struct kvm_cpu_context *host_ctxt)
@@ -737,6 +740,8 @@ void handle_trap(struct kvm_cpu_context *host_ctxt)
 {
 	u64 esr = read_sysreg_el2(SYS_ESR);
 
+	trace_hyp_enter();
+
 	switch (ESR_ELx_EC(esr)) {
 	case ESR_ELx_EC_HVC64:
 		handle_host_hcall(host_ctxt);
@@ -751,4 +756,6 @@ void handle_trap(struct kvm_cpu_context *host_ctxt)
 	default:
 		BUG();
 	}
+
+	trace_hyp_exit();
 }
diff --git a/arch/arm64/kvm/hyp/nvhe/psci-relay.c b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
index c3e196fb8b18..64d1d418df1d 100644
--- a/arch/arm64/kvm/hyp/nvhe/psci-relay.c
+++ b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
@@ -6,11 +6,12 @@
 
 #include <asm/kvm_asm.h>
 #include <asm/kvm_hyp.h>
+#include <asm/kvm_hypevents.h>
 #include <asm/kvm_mmu.h>
-#include <linux/arm-smccc.h>
 #include <linux/kvm_host.h>
 #include <uapi/linux/psci.h>
 
+#include <nvhe/arm-smccc.h>
 #include <nvhe/memory.h>
 #include <nvhe/trap_handler.h>
 
@@ -205,6 +206,7 @@ asmlinkage void __noreturn __kvm_host_psci_cpu_entry(bool is_cpu_on)
 	struct psci_boot_args *boot_args;
 	struct kvm_cpu_context *host_ctxt;
 
+	trace_hyp_enter();
 	host_ctxt = host_data_ptr(host_ctxt);
 
 	if (is_cpu_on)
@@ -221,6 +223,7 @@ asmlinkage void __noreturn __kvm_host_psci_cpu_entry(bool is_cpu_on)
 	write_sysreg_el1(INIT_SCTLR_EL1_MMU_OFF, SYS_SCTLR);
 	write_sysreg(INIT_PSTATE_EL1, SPSR_EL2);
 
+	trace_hyp_exit();
 	__host_enter(host_ctxt);
 }
 
diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
index 7d2ba6ef0261..bbe035acda89 100644
--- a/arch/arm64/kvm/hyp/nvhe/switch.c
+++ b/arch/arm64/kvm/hyp/nvhe/switch.c
@@ -7,7 +7,6 @@
 #include <hyp/switch.h>
 #include <hyp/sysreg-sr.h>
 
-#include <linux/arm-smccc.h>
 #include <linux/kvm_host.h>
 #include <linux/types.h>
 #include <linux/jump_label.h>
@@ -21,6 +20,7 @@
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_hyp.h>
+#include <asm/kvm_hypevents.h>
 #include <asm/kvm_mmu.h>
 #include <asm/fpsimd.h>
 #include <asm/debug-monitors.h>
@@ -349,10 +349,13 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
 	__debug_switch_to_guest(vcpu);
 
 	do {
+		trace_hyp_exit();
+
 		/* Jump in the fire! */
 		exit_code = __guest_enter(vcpu);
 
 		/* And we're baaack! */
+		trace_hyp_enter();
 	} while (fixup_guest_exit(vcpu, &exit_code));
 
 	__sysreg_save_state_nvhe(guest_ctxt);
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 23/24] KVM: arm64: Add selftest event support to pKVM hyp

[Vincent Donnefort]

Add a selftest event that can be triggered from a `write_event` tracefs
file. This intends to be used by trace remote selftests.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 79019e11f529..522cccef32b7 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -94,6 +94,7 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_reset_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_swap_reader_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_enable_event,
+	__KVM_HOST_SMCCC_FUNC___pkvm_write_event,
 };
 
 #define DECLARE_KVM_VHE_SYM(sym)	extern char sym[]
diff --git a/arch/arm64/include/asm/kvm_hypevents.h b/arch/arm64/include/asm/kvm_hypevents.h
index ce3953bc884a..3d1244972869 100644
--- a/arch/arm64/include/asm/kvm_hypevents.h
+++ b/arch/arm64/include/asm/kvm_hypevents.h
@@ -24,4 +24,18 @@ HYP_EVENT(hyp_exit,
 	),
 	HE_PRINTK()
 );
+
+#ifdef CONFIG_PKVM_SELFTESTS
+HYP_EVENT(selftest,
+	HE_PROTO(u64 id),
+	HE_STRUCT(
+		he_field(u64, id)
+	),
+	HE_ASSIGN(
+		__entry->id = id;
+	),
+	RE_PRINTK("id=%lld", __entry->id)
+);
 #endif
+
+#endif /* __ARM64_KVM_HYPEVENTS_H_ */
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index f7d1d8987cce..333824325c9e 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -46,6 +46,7 @@ menuconfig KVM
 config NVHE_EL2_DEBUG
 	bool "Debug mode for non-VHE EL2 object"
 	depends on KVM
+	select PKVM_SELFTESTS
 	help
 	  Say Y here to enable the debug mode for the non-VHE KVM EL2 object.
 	  Failure reports will BUG() in the hypervisor. This is intended for
@@ -83,6 +84,15 @@ config PTDUMP_STAGE2_DEBUGFS
 
 	  If in doubt, say N.
 
+config PKVM_SELFTESTS
+	bool "Protected KVM hypervisor selftests"
+	depends on KVM
+	default n
+	help
+	  Say Y here to enable pKVM hypervisor testing infrastructure.
+
+	  If unsure, say N.
+
 config PKVM_TRACING
 	bool
 	depends on KVM
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 7d7d0c07a6d4..e6b45631c48b 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -628,6 +628,20 @@ static void handle___pkvm_enable_event(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) = __pkvm_enable_event(id, enable);
 }
 
+static void handle___pkvm_write_event(struct kvm_cpu_context *host_ctxt)
+{
+	int smc_ret = SMCCC_RET_NOT_SUPPORTED, ret = -EOPNOTSUPP;
+#ifdef CONFIG_PKVM_SELFTESTS
+	DECLARE_REG(u64, id, host_ctxt, 1);
+
+	trace_selftest(id);
+	smc_ret = SMCCC_RET_SUCCESS;
+	ret = 0;
+#endif
+	cpu_reg(host_ctxt, 0) = smc_ret;
+	cpu_reg(host_ctxt, 1) = ret;
+}
+
 typedef void (*hcall_t)(struct kvm_cpu_context *);
 
 #define HANDLE_FUNC(x)	[__KVM_HOST_SMCCC_FUNC_##x] = (hcall_t)handle_##x
@@ -674,6 +688,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_reset_tracing),
 	HANDLE_FUNC(__pkvm_swap_reader_tracing),
 	HANDLE_FUNC(__pkvm_enable_event),
+	HANDLE_FUNC(__pkvm_write_event),
 };
 
 static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 1a4313362aa0..ee3af685d8dc 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -317,8 +317,34 @@ static int hyp_trace_clock_show(struct seq_file *m, void *v)
 }
 DEFINE_SHOW_ATTRIBUTE(hyp_trace_clock);
 
+#ifdef CONFIG_PKVM_SELFTESTS
+static ssize_t hyp_trace_write_event_write(struct file *f, const char __user *ubuf,
+					   size_t cnt, loff_t *pos)
+{
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+	if (ret)
+		return ret;
+
+	ret = kvm_call_hyp_nvhe(__pkvm_write_event, val);
+	if (ret)
+		return ret;
+
+	return cnt;
+}
+
+static const struct file_operations hyp_trace_write_event_fops = {
+	.write	= hyp_trace_write_event_write,
+};
+#endif
+
 static int hyp_trace_init_tracefs(struct dentry *d, void *priv)
 {
+#ifdef CONFIG_PKVM_SELFTESTS
+	tracefs_create_file("write_event", 0200, d, NULL, &hyp_trace_write_event_fops);
+#endif
 	return tracefs_create_file("trace_clock", 0440, d, NULL, &hyp_trace_clock_fops) ?
 		0 : -ENOMEM;
 }
-- 
2.49.0.967.g6a0df3ecc3-goog

[PATCH v4 24/24] tracing: selftests: Add pKVM trace remote tests

[Vincent Donnefort]

Run the trace remote selftests with the pKVM trace remote "hypervisor".

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/tools/testing/selftests/ftrace/test.d/remotes/pkvm/buffer_size.tc b/tools/testing/selftests/ftrace/test.d/remotes/pkvm/buffer_size.tc
new file mode 100644
index 000000000000..383ef7a84274
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/pkvm/buffer_size.tc
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test pkvm hypervisor tracing buffer size
+
+SOURCE_REMOTE_TEST=1
+. $TEST_DIR/remotes/buffer_size.tc
+
+set -e
+setup_remote "hypervisor"
+test_buffer_size
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/pkvm/reset.tc b/tools/testing/selftests/ftrace/test.d/remotes/pkvm/reset.tc
new file mode 100644
index 000000000000..679e31257d0b
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/pkvm/reset.tc
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test pkvm hypervisor tracing reset
+
+SOURCE_REMOTE_TEST=1
+. $TEST_DIR/remotes/reset.tc
+
+set -e
+setup_remote "hypervisor"
+test_reset
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/pkvm/trace_pipe.tc b/tools/testing/selftests/ftrace/test.d/remotes/pkvm/trace_pipe.tc
new file mode 100644
index 000000000000..4c77431e884f
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/pkvm/trace_pipe.tc
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test pkvm hypervisor tracing pipe
+
+SOURCE_REMOTE_TEST=1
+. $TEST_DIR/remotes/trace_pipe.tc
+
+set -e
+setup_remote "hypervisor"
+test_trace_pipe
diff --git a/tools/testing/selftests/ftrace/test.d/remotes/pkvm/unloading.tc b/tools/testing/selftests/ftrace/test.d/remotes/pkvm/unloading.tc
new file mode 100644
index 000000000000..059c7ad1c008
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/pkvm/unloading.tc
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test pkvm hypervisor tracing buffer unloading
+
+SOURCE_REMOTE_TEST=1
+. $TEST_DIR/remotes/unloading.tc
+
+set -e
+setup_remote "hypervisor"
+test_unloading
-- 
2.49.0.967.g6a0df3ecc3-goog

Re: [PATCH v4 01/24] ring-buffer: Introduce ring-buffer remotes

[Steven Rostedt]

On Tue,  6 May 2025 17:47:57 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:


> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index 56e27263acf8..c0c7f8a0dcb3 100644
> --- a/include/linux/ring_buffer.h
> +++ b/include/linux/ring_buffer.h
> @@ -248,4 +248,67 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
>  		    struct vm_area_struct *vma);
>  int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
>  int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
> +
> +#define meta_pages_lost(__meta) \
> +	((__meta)->Reserved1)
> +#define meta_pages_touched(__meta) \
> +	((__meta)->Reserved2)

Hmm, I wonder if this would be worth adding to the user interface?

> +
> +struct ring_buffer_desc {
> +	int		cpu;
> +	unsigned int	nr_page_va; /* excludes the meta page */
> +	unsigned long	meta_va;
> +	unsigned long	page_va[];

	unsigned long page_val[] __counted_by(nr_page_va);

?

Or is this too hidden by the remote?

> +};
> +
> +struct trace_buffer_desc {
> +	int		nr_cpus;
> +	size_t		struct_len;
> +	char		__data[]; /* list of ring_buffer_desc */
> +};
> +
> +static inline struct ring_buffer_desc *__next_ring_buffer_desc(struct ring_buffer_desc *desc)
> +{
> +	size_t len = struct_size(desc, page_va, desc->nr_page_va);
> +
> +	return (struct ring_buffer_desc *)((void *)desc + len);
> +}
> +
> +static inline struct ring_buffer_desc *__first_ring_buffer_desc(struct trace_buffer_desc *desc)
> +{
> +	return (struct ring_buffer_desc *)(&desc->__data[0]);
> +}
> +
> +static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned int nr_cpus)
> +{
> +	unsigned int nr_pages = (PAGE_ALIGN(buffer_size) / PAGE_SIZE) + 1;

Hmm,

	unsigned int nr_pages = (buffer_size + (PAGE_SIZE - 1)) / PAGE_SIZE;

?

Of course buffer_size of zero is zero here. But is buffer_size of zero what we want?

> +	struct ring_buffer_desc *rbdesc;
> +
> +	return size_add(offsetof(struct trace_buffer_desc, __data),
> +			size_mul(nr_cpus, struct_size(rbdesc, page_va, nr_pages)));
> +}
> +
> +#define for_each_ring_buffer_desc(__pdesc, __cpu, __trace_pdesc)		\
> +	for (__pdesc = __first_ring_buffer_desc(__trace_pdesc), __cpu = 0;	\
> +	     __cpu < (__trace_pdesc)->nr_cpus;					\
> +	     __cpu++, __pdesc = __next_ring_buffer_desc(__pdesc))

Probably should add parenthesis:

#define for_each_ring_buffer_desc(__pdesc, __cpu, __trace_pdesc)		\
	for (__pdesc = __first_ring_buffer_desc(__trace_pdesc), __cpu = 0;	\
	     (__cpu) < (__trace_pdesc)->nr_cpus;					\
	     (__cpu)++, __pdesc = __next_ring_buffer_desc(__pdesc))

Especially if __cpu is passed in as "*pcpu"

> +
> +struct ring_buffer_remote {
> +	struct trace_buffer_desc	*desc;
> +	int				(*swap_reader_page)(unsigned int cpu, void *priv);
> +	int				(*reset)(unsigned int cpu, void *priv);
> +	void				*priv;
> +};
> +
> +int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu);
> +
> +struct trace_buffer *
> +__ring_buffer_alloc_remote(struct ring_buffer_remote *remote,
> +			   struct lock_class_key *key);
> +
> +#define ring_buffer_remote(remote)				\
> +({								\
> +	static struct lock_class_key __key;			\
> +	__ring_buffer_alloc_remote(remote, &__key);		\
> +})
>  #endif /* _LINUX_RING_BUFFER_H */
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index c0f877d39a24..a96a0b231fee 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -523,6 +523,8 @@ struct ring_buffer_per_cpu {
>  	struct trace_buffer_meta	*meta_page;
>  	struct ring_buffer_cpu_meta	*ring_meta;
>  
> +	struct ring_buffer_remote	*remote;
> +
>  	/* ring buffer pages to update, > 0 to add, < 0 to remove */
>  	long				nr_pages_to_update;
>  	struct list_head		new_pages; /* new pages to add */
> @@ -545,6 +547,8 @@ struct trace_buffer {
>  
>  	struct ring_buffer_per_cpu	**buffers;
>  
> +	struct ring_buffer_remote	*remote;
> +
>  	struct hlist_node		node;
>  	u64				(*clock)(void);
>  
> @@ -2196,6 +2200,41 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
>  	return -ENOMEM;
>  }
>  
> +static struct ring_buffer_desc *ring_buffer_desc(struct trace_buffer_desc *trace_desc, int cpu)
> +{
> +	struct ring_buffer_desc *desc, *end;
> +	size_t len;
> +	int i;
> +
> +	if (!trace_desc)
> +		return NULL;
> +
> +	if (cpu >= trace_desc->nr_cpus)
> +		return NULL;
> +
> +	end = (struct ring_buffer_desc *)((void *)trace_desc + trace_desc->struct_len);
> +	desc = __first_ring_buffer_desc(trace_desc);
> +	len = struct_size(desc, page_va, desc->nr_page_va);
> +	desc = (struct ring_buffer_desc *)((void *)desc + (len * cpu));
> +
> +	if (desc < end && desc->cpu == cpu)
> +		return desc;
> +
> +	/* Missing CPUs, need to linear search */
> +	for_each_ring_buffer_desc(desc, i, trace_desc) {
> +		if (desc->cpu == cpu)
> +			return desc;
> +	}
> +
> +	return NULL;
> +}
> +
> +static void *ring_buffer_desc_page(struct ring_buffer_desc *desc, int page_id)
> +{
> +	return page_id > desc->nr_page_va ? NULL : (void *)desc->page_va[page_id];
> +}
> +
> +
>  static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
>  			     unsigned long nr_pages)
>  {
> @@ -2256,6 +2295,30 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
>  
>  	cpu_buffer->reader_page = bpage;
>  
> +	if (buffer->remote) {
> +		struct ring_buffer_desc *desc = ring_buffer_desc(buffer->remote->desc, cpu);
> +
> +		if (!desc)
> +			goto fail_free_reader;
> +
> +		cpu_buffer->remote = buffer->remote;
> +		cpu_buffer->meta_page = (struct trace_buffer_meta *)(void *)desc->meta_va;
> +		cpu_buffer->subbuf_ids = desc->page_va;
> +		cpu_buffer->nr_pages = desc->nr_page_va - 1;

Probably should add a comment here:

		/* Remote buffers are read only and immutable */

> +		atomic_inc(&cpu_buffer->record_disabled);
> +		atomic_inc(&cpu_buffer->resize_disabled);
> +
> +		bpage->page = ring_buffer_desc_page(desc, cpu_buffer->meta_page->reader.id);
> +		if (!bpage->page)
> +			goto fail_free_reader;
> +		/*
> +		 * The meta-page can only describe which of the ring-buffer page
> +		 * is the reader. There is no need to init the rest of the
> +		 * ring-buffer.
> +		 */
> +		return cpu_buffer;
> +	}
> +
>  	if (buffer->range_addr_start) {
>  		/*
>  		 * Range mapped buffers have the same restrictions as memory
> @@ -2333,6 +2396,10 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
>  
>  	irq_work_sync(&cpu_buffer->irq_work.work);
>  
> +	/* remote ring-buffer. We do not own the data pages */
> +	if (cpu_buffer->remote)
> +		cpu_buffer->reader_page->page = NULL;
> +
>  	free_buffer_page(cpu_buffer->reader_page);
>  
>  	if (head) {
> @@ -2355,7 +2422,8 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
>  					 int order, unsigned long start,
>  					 unsigned long end,
>  					 unsigned long scratch_size,
> -					 struct lock_class_key *key)
> +					 struct lock_class_key *key,
> +					 struct ring_buffer_remote *remote)
>  {
>  	struct trace_buffer *buffer;
>  	long nr_pages;
> @@ -2383,6 +2451,11 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
>  	buffer->flags = flags;
>  	buffer->clock = trace_clock_local;
>  	buffer->reader_lock_key = key;
> +	if (remote) {
> +		buffer->remote = remote;
> +		/* The writer is remote. This ring-buffer is read-only */
> +		atomic_inc(&buffer->record_disabled);
> +	}
>  
>  	init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
>  	init_waitqueue_head(&buffer->irq_work.waiters);
> @@ -2502,7 +2575,7 @@ struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
>  					struct lock_class_key *key)
>  {
>  	/* Default buffer page size - one system page */
> -	return alloc_buffer(size, flags, 0, 0, 0, 0, key);
> +	return alloc_buffer(size, flags, 0, 0, 0, 0, key, NULL);
>  
>  }
>  EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
> @@ -2529,7 +2602,18 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
>  					       struct lock_class_key *key)
>  {
>  	return alloc_buffer(size, flags, order, start, start + range_size,
> -			    scratch_size, key);
> +			    scratch_size, key, NULL);
> +}
> +
> +/**
> + * __ring_buffer_alloc_remote - allocate a new ring_buffer from a remote
> + * @remote: Contains a description of the ring-buffer pages and remote callbacks.
> + * @key: ring buffer reader_lock_key.
> + */
> +struct trace_buffer *__ring_buffer_alloc_remote(struct ring_buffer_remote *remote,
> +						struct lock_class_key *key)
> +{
> +	return alloc_buffer(0, 0, 0, 0, 0, 0, key, remote);
>  }
>  
>  void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size)
> @@ -5278,8 +5362,56 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
>  	}
>  }
>  
> +static bool rb_read_remote_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
> +{
> +	local_set(&cpu_buffer->entries, READ_ONCE(cpu_buffer->meta_page->entries));
> +	local_set(&cpu_buffer->overrun, READ_ONCE(cpu_buffer->meta_page->overrun));
> +	local_set(&cpu_buffer->pages_touched, READ_ONCE(meta_pages_touched(cpu_buffer->meta_page)));
> +	local_set(&cpu_buffer->pages_lost, READ_ONCE(meta_pages_lost(cpu_buffer->meta_page)));
> +	/*
> +	 * No need to get the "read" field, it can be tracked here as any
> +	 * reader will have to go through a rign_buffer_per_cpu.
> +	 */
> +
> +	return rb_num_of_entries(cpu_buffer);
> +}
> +
>  static struct buffer_page *
> -rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
> +__rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer)
> +{
> +	u32 prev_reader;
> +
> +	if (!rb_read_remote_meta_page(cpu_buffer))
> +		return NULL;
> +
> +	/* More to read on the reader page */
> +	if (cpu_buffer->reader_page->read < rb_page_size(cpu_buffer->reader_page)) {
> +		if (!cpu_buffer->reader_page->read)
> +			cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
> +		return cpu_buffer->reader_page;
> +	}
> +
> +	prev_reader = cpu_buffer->meta_page->reader.id;
> +
> +	WARN_ON(cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu, cpu_buffer->remote->priv));

Please always use WARN_ON_ONCE() we don't need to spam the console when things go wrong.

> +	/* nr_pages doesn't include the reader page */
> +	if (WARN_ON(cpu_buffer->meta_page->reader.id > cpu_buffer->nr_pages))
> +		return NULL;
> +
> +	cpu_buffer->reader_page->page =
> +		(void *)cpu_buffer->subbuf_ids[cpu_buffer->meta_page->reader.id];
> +	cpu_buffer->reader_page->id = cpu_buffer->meta_page->reader.id;
> +	cpu_buffer->reader_page->read = 0;
> +	cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
> +	cpu_buffer->lost_events = cpu_buffer->meta_page->reader.lost_events;
> +
> +	WARN_ON(prev_reader == cpu_buffer->meta_page->reader.id);
> +
> +	return rb_page_size(cpu_buffer->reader_page) ? cpu_buffer->reader_page : NULL;
> +}

-- Steve

Re: [PATCH v4 02/24] tracing: Introduce trace remotes

[Steven Rostedt]

On Tue,  6 May 2025 17:47:58 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:

> +
> +static bool trace_remote_loaded(struct trace_remote *remote)
> +{
> +	return remote->trace_buffer;
> +}
> +
> +static bool trace_remote_busy(struct trace_remote *remote)

Can you add comments to what these functions are doing?

Doesn't need to be kerneldoc (it actually shouldn't be), but describe why
they would return true and why they would return false.

> +{
> +	return trace_remote_loaded(remote) &&
> +		(remote->nr_readers || remote->tracing_on ||
> +		 !ring_buffer_empty(remote->trace_buffer));
> +}
> +
> +static int trace_remote_load(struct trace_remote *remote)
> +{
> +	struct ring_buffer_remote *rb_remote = &remote->rb_remote;
> +
> +	lockdep_assert_held(&remote->lock);
> +
> +	if (trace_remote_loaded(remote))
> +		return 0;
> +
> +	remote->trace_buffer_desc = remote->cbs->load_trace_buffer(remote->trace_buffer_size,
> +								   remote->priv);
> +	if (!remote->trace_buffer_desc)
> +		return -ENOMEM;

The error may not be -ENOMEM, have the load_trace_buffer return an ERR_PTR
and then you can return:

	if (IS_ERR(remote->trace_buffer_desc)
		return PTR_ERR(remote->trace_buffer_desc);


> +
> +	rb_remote->desc = remote->trace_buffer_desc;
> +	rb_remote->swap_reader_page = remote->cbs->swap_reader_page;
> +	rb_remote->priv = remote->priv;
> +	remote->trace_buffer = ring_buffer_remote(rb_remote);
> +	if (!remote->trace_buffer) {

Same here.

> +		remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv);
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +
> +static void trace_remote_unload(struct trace_remote *remote)
> +{
> +	lockdep_assert_held(&remote->lock);
> +
> +	if (!trace_remote_loaded(remote) || trace_remote_busy(remote))
> +		return;

Can this cause leaks? Should trace_remote_unload() return an error value to
let the caller know it wasn't unloaded?

> +
> +	ring_buffer_free(remote->trace_buffer);
> +	remote->trace_buffer = NULL;
> +	remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv);
> +}
> +

Short description of what trace_remote_start does.

> +static int trace_remote_start(struct trace_remote *remote)
> +{
> +	int ret;
> +
> +	lockdep_assert_held(&remote->lock);
> +
> +	if (remote->tracing_on)
> +		return 0;
> +
> +	ret = trace_remote_load(remote);
> +	if (ret)
> +		return ret;
> +
> +	ret = remote->cbs->enable_tracing(true, remote->priv);
> +	if (ret) {
> +		trace_remote_unload(remote);
> +		return ret;
> +	}
> +
> +	remote->tracing_on = true;
> +
> +	return 0;
> +}
> +

Same for stop.

-- Steve

> +static int trace_remote_stop(struct trace_remote *remote)
> +{
> +	int ret;
> +
> +	lockdep_assert_held(&remote->lock);
> +
> +	if (!remote->tracing_on)
> +		return 0;
> +
> +	ret = remote->cbs->enable_tracing(false, remote->priv);
> +	if (ret)
> +		return ret;
> +
> +	ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS);
> +	remote->tracing_on = false;
> +	trace_remote_unload(remote);
> +
> +	return 0;
> +}

Re: [PATCH v4 01/24] ring-buffer: Introduce ring-buffer remotes

[Vincent Donnefort]

On Wed, May 07, 2025 at 07:47:22PM -0400, Steven Rostedt wrote:
> On Tue,  6 May 2025 17:47:57 +0100
> Vincent Donnefort <vdonnefort@google.com> wrote:
> 
> 
> > diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> > index 56e27263acf8..c0c7f8a0dcb3 100644
> > --- a/include/linux/ring_buffer.h
> > +++ b/include/linux/ring_buffer.h
> > @@ -248,4 +248,67 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
> >  		    struct vm_area_struct *vma);
> >  int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
> >  int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
> > +
> > +#define meta_pages_lost(__meta) \
> > +	((__meta)->Reserved1)
> > +#define meta_pages_touched(__meta) \
> > +	((__meta)->Reserved2)
> 
> Hmm, I wonder if this would be worth adding to the user interface?

Would trace-cmd have any use for those fields? That said, even if it does not at
the moment, it would mean the meta-page has a single version between
kern/user-space and hyp/kern which is probably better?

I can add an additional patch in this series to extend the meta-page.

[...]

Re: [PATCH v4 02/24] tracing: Introduce trace remotes

[Vincent Donnefort]

[...]
> > +		remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv);
> > +		return -ENOMEM;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static void trace_remote_unload(struct trace_remote *remote)
> > +{
> > +	lockdep_assert_held(&remote->lock);
> > +
> > +	if (!trace_remote_loaded(remote) || trace_remote_busy(remote))
> > +		return;
> 
> Can this cause leaks? Should trace_remote_unload() return an error value to
> let the caller know it wasn't unloaded?

No risk of leak here. This acts a like a refcount to make sure the buffer is
unloaded only when no one is reading and tracing_on=0.


[...]

Re: [PATCH v4 01/24] ring-buffer: Introduce ring-buffer remotes

[Steven Rostedt]

On Thu, 8 May 2025 10:10:40 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:

> > Hmm, I wonder if this would be worth adding to the user interface?  
> 
> Would trace-cmd have any use for those fields? That said, even if it does not at
> the moment, it would mean the meta-page has a single version between
> kern/user-space and hyp/kern which is probably better?

I was thinking that it's better to have the consistency than user space
using it. I'm not sure how much overhead it has for the normal buffer to
update those fields.

-- Steve

Re: [PATCH v4 05/24] tracing: Add events to trace remotes

[Steven Rostedt]

On Tue,  6 May 2025 17:48:01 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:

> diff --git a/include/linux/trace_remote_event.h b/include/linux/trace_remote_event.h
> new file mode 100644
> index 000000000000..621c5dff0664
> --- /dev/null
> +++ b/include/linux/trace_remote_event.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _LINUX_TRACE_REMOTE_EVENTS_H
> +#define _LINUX_TRACE_REMOTE_EVENTS_H
> +
> +struct trace_remote;
> +struct trace_event_fields;
> +
> +struct remote_event_hdr {
> +	unsigned short	id;
> +};
> +
> +#define REMOTE_EVENT_NAME_MAX 29

29 is a particularly strange number. It's not even divisible by
sizeof(short). This will leave a hole in the remote_event structure.

Should it be "30" to plug up that one byte space between name and "id"?

-- Steve

> +struct remote_event {
> +	char				name[REMOTE_EVENT_NAME_MAX];
> +	unsigned short			id;
> +	bool				enabled;
> +	struct trace_remote		*remote;
> +	struct trace_event_fields	*fields;
> +	char				*print_fmt;
> +	void				(*print)(void *evt, struct trace_seq *seq);
> +};

Re: [PATCH v4 08/24] ring-buffer: Expose buffer_data_page material

[Steven Rostedt]

On Tue,  6 May 2025 17:48:04 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:

> In preparation for allowing the write of ring-buffer compliant pages
> outside of ring_buffer.c, move buffer_data_page and timestamps
> encoding functions into the publicly available ring_buffer.h.
> 
> Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

Let's create a new file for this instead of adding it to ring_buffer.h.
Although it's being used by remote buffers, I rather not make this
something that people may think they can access anywhere.

Perhaps: ring_buffer_types.h

with a comment stating that these are to be used by the remote ring buffers
and the ring buffer internals and should not be used directly.

-- Steve

Re: [PATCH v4 05/24] tracing: Add events to trace remotes

[Vincent Donnefort]

On Fri, May 09, 2025 at 03:47:35PM -0400, Steven Rostedt wrote:
> On Tue,  6 May 2025 17:48:01 +0100
> Vincent Donnefort <vdonnefort@google.com> wrote:
> 
> > diff --git a/include/linux/trace_remote_event.h b/include/linux/trace_remote_event.h
> > new file mode 100644
> > index 000000000000..621c5dff0664
> > --- /dev/null
> > +++ b/include/linux/trace_remote_event.h
> > @@ -0,0 +1,23 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +
> > +#ifndef _LINUX_TRACE_REMOTE_EVENTS_H
> > +#define _LINUX_TRACE_REMOTE_EVENTS_H
> > +
> > +struct trace_remote;
> > +struct trace_event_fields;
> > +
> > +struct remote_event_hdr {
> > +	unsigned short	id;
> > +};
> > +
> > +#define REMOTE_EVENT_NAME_MAX 29
> 
> 29 is a particularly strange number. It's not even divisible by
> sizeof(short). This will leave a hole in the remote_event structure.
> 
> Should it be "30" to plug up that one byte space between name and "id"?

Ha yes 30 is what it should be!

> 
> -- Steve
> 
> > +struct remote_event {
> > +	char				name[REMOTE_EVENT_NAME_MAX];
> > +	unsigned short			id;
> > +	bool				enabled;
> > +	struct trace_remote		*remote;
> > +	struct trace_event_fields	*fields;
> > +	char				*print_fmt;
> > +	void				(*print)(void *evt, struct trace_seq *seq);
> > +};

Re: [PATCH v4 00/24] Tracefs support for pKVM

[Steven Rostedt]

On Tue,  6 May 2025 17:47:56 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:

> The growing set of features supported by the hypervisor in protected
> mode necessitates debugging and profiling tools. Tracefs is the
> ideal candidate for this task:
> 
>   * It is simple to use and to script.
> 
>   * It is supported by various tools, from the trace-cmd CLI to the
>     Android web-based perfetto.
> 
>   * The ring-buffer, where are stored trace events consists of linked
>     pages, making it an ideal structure for sharing between kernel and
>     hypervisor.
> 
> This series first introduces a new generic way of creating remote events and
> remote buffers. Then it adds support to the pKVM hypervisor.
> 
> 1. ring-buffer
> --------------
> 
> To setup the per-cpu ring-buffers, a new interface is created:
> 
>   ring_buffer_remote:	Describes what the kernel needs to know about the
> 			remote writer, that is, the set of pages forming the
> 			ring-buffer and a callback for the reader/head
> 			swapping (enables consuming read)
> 
>   ring_buffer_remote():	Creates a read-only ring-buffer from a
> 			ring_buffer_remote.
> 
> To keep the internals of `struct ring_buffer` in sync with the remote,
> the meta-page is used. It was originally introduced to enable user-space
> mapping of the ring-buffer [1]. In this case, the kernel is not the
> producer anymore but the reader. The function to read that meta-page is:
> 
>   ring_buffer_poll_remote():
> 			Update `struct ring_buffer` based on the remote
> 			meta-page. Wake-up readers if necessary.
> 
> The kernel has to poll the meta-page to be notified of newly written
> events.
> 
> 2. Tracefs
> ----------
> 
> This series introduce a new trace_remote that does the link between
> tracefs and the remote ring-buffer.
> 
> The interface is found in the remotes/ directory at the root of the
> tracefs mount point. Each remote is like an instance and you'll find
> there a subset of the regular Tracefs user-space interface:
> 
>   remotes/test/
>      buffer_size_kb
>      trace_clock
>      trace_pipe
>      trace
>      per_cpu/
>              cpuX/
>                  trace
>                  trace_pipe
>      events/
> 
>             test/
>                 selftest/
>                           enable
>                           id
> 
> Behind the scenes, kernel/trace/trace_remote.c creates this tracefs
> hierarchy without relying on kernel/trace/trace.c. This is due to
> fundamental differences:
> 
>   * Remote tracing doesn't support trace_array's system-specific
>     features (snapshots, tracers, etc.).
> 
>   * Logged event formats differ (e.g., no PID for remote events).
> 
>   * Buffer operations require specific remote interactions.
> 
> 3. Simple Ring-Buffer
> ---------------------
> 
> As the current ring-buffer.c implementation has too many dependencies to
> be used directly by the pKVM hypervisor. A new simple implementation is
> created and can be found in kernel/trace/simple-ring-buffer.c.
> 
> This implementation is write-only and is used by both the pKVM
> hypervisor and a trace_remote test module.
> 
> 4. Events
> ---------
> 
> A new REMOTE_EVENT() macro is added to simplify the creation of events
> on the kernel side. As remote tracing buffer are read only, only the
> event structure and a way of printing must be declared. The prototype of
> the macro is very similar to the well-known TRACE_EVENT()
> 
>  REMOTE_EVENT(my_event, id,
>      RE_STRUCT(
>          re_field(u64, foobar)
>      ),
>      RE_PRINTK("foobar=%lld", __entry->foobar)
>      )
>   )
> 
> 5. pKVM
> -------
> 
> The pKVM support simply creates a "hypervisor" trace_remote on the
> kernel side and inherits from simple-ring-buffer.c on the hypervisor
> side.
> 
> A new event macro is created HYP_EVENT() that is under the hood re-using
> REMOTE_EVENT() (defined in the previous paragaph) as well as generate
> hypervisor specific struct and trace_<event>() functions.
> 
> 5. Limitations:
> ---------------
> 
> Non-consuming reading of the buffer isn't supported (i.e. cat trace ->
> -EPERM) due to current the lack of support in the ring-buffer meta-page.
> 
> [1] https://tracingsummit.org/ts/2022/hypervisortracing/
> [2] https://lore.kernel.org/all/20240510140435.3550353-1-vdonnefort@google.com/
> 

BTW,  I tried to build this series and it fails.

  CALL    /work/git/test-linux.git/scripts/checksyscalls.sh
  CC      kernel/trace/simple_ring_buffer.o
In file included from ./arch/x86/include/generated/asm/rwonce.h:1,
                 from /work/git/test-linux.git/include/linux/compiler.h:390,
                 from /work/git/test-linux.git/arch/x86/include/asm/atomic.h:5,
                 from /work/git/test-linux.git/include/linux/atomic.h:7,
                 from /work/git/test-linux.git/kernel/trace/simple_ring_buffer.c:7:
/work/git/test-linux.git/kernel/trace/simple_ring_buffer.c: In function ‘simple_rb_move_tail’:
/work/git/test-linux.git/include/asm-generic/rwonce.h:55:37: error: assignment to ‘struct list_head *’ from ‘long unsigned int’ makes pointer from integer without a cast [-Wint-conversion]
   55 |         *(volatile typeof(x) *)&(x) = (val);                            \
      |                                     ^
/work/git/test-linux.git/include/asm-generic/rwonce.h:61:9: note: in expansion of macro ‘__WRITE_ONCE’
   61 |         __WRITE_ONCE(x, val);                                           \
      |         ^~~~~~~~~~~~
/work/git/test-linux.git/arch/x86/include/asm/barrier.h:63:9: note: in expansion of macro ‘WRITE_ONCE’
   63 |         WRITE_ONCE(*p, v);                                              \
      |         ^~~~~~~~~~
/work/git/test-linux.git/include/asm-generic/barrier.h:172:55: note: in expansion of macro ‘__smp_store_release’
  172 | #define smp_store_release(p, v) do { kcsan_release(); __smp_store_release(p, v); } while (0)
      |                                                       ^~~~~~~~~~~~~~~~~~~
/work/git/test-linux.git/kernel/trace/simple_ring_buffer.c:129:17: note: in expansion of macro ‘smp_store_release’
  129 |                 smp_store_release(&new_tail->list.next,
      |                 ^~~~~~~~~~~~~~~~~
make[5]: *** [/work/git/test-linux.git/scripts/Makefile.build:203: kernel/trace/simple_ring_buffer.o] Error 1
make[4]: *** [/work/git/test-linux.git/scripts/Makefile.build:461: kernel/trace] Error 2
make[3]: *** [/work/git/test-linux.git/scripts/Makefile.build:461: kernel] Error 2
make[2]: *** [/work/git/test-linux.git/Makefile:2004: .] Error 2
make[1]: *** [/work/git/test-linux.git/Makefile:248: __sub-make] Error 2
make[1]: Leaving directory '/work/build/trace/nobackup/debiantesting-x86-64'

Even when I fixed this, it then failed with the building of the sample module.

I think you need something like:

obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test_mod.o

remote_test_mod-y := simple_ring_buffer.o remote_test.o trace_remote.o

If the module needs more than one object file. Then the module should be
called something that doesn't have a .c file and use that name with ".o" to
add all the objects.

I think this could work, but this still had issues with functions not exported.

-- Steve

Re: [PATCH v4 00/24] Tracefs support for pKVM

[Vincent Donnefort]

On Wed, May 14, 2025 at 01:38:15PM -0400, Steven Rostedt wrote:
> On Tue,  6 May 2025 17:47:56 +0100
> Vincent Donnefort <vdonnefort@google.com> wrote:
> 
> > The growing set of features supported by the hypervisor in protected
> > mode necessitates debugging and profiling tools. Tracefs is the
> > ideal candidate for this task:
> > 
> >   * It is simple to use and to script.
> > 
> >   * It is supported by various tools, from the trace-cmd CLI to the
> >     Android web-based perfetto.
> > 
> >   * The ring-buffer, where are stored trace events consists of linked
> >     pages, making it an ideal structure for sharing between kernel and
> >     hypervisor.
> > 
> > This series first introduces a new generic way of creating remote events and
> > remote buffers. Then it adds support to the pKVM hypervisor.
> > 
> > 1. ring-buffer
> > --------------
> > 
> > To setup the per-cpu ring-buffers, a new interface is created:
> > 
> >   ring_buffer_remote:	Describes what the kernel needs to know about the
> > 			remote writer, that is, the set of pages forming the
> > 			ring-buffer and a callback for the reader/head
> > 			swapping (enables consuming read)
> > 
> >   ring_buffer_remote():	Creates a read-only ring-buffer from a
> > 			ring_buffer_remote.
> > 
> > To keep the internals of `struct ring_buffer` in sync with the remote,
> > the meta-page is used. It was originally introduced to enable user-space
> > mapping of the ring-buffer [1]. In this case, the kernel is not the
> > producer anymore but the reader. The function to read that meta-page is:
> > 
> >   ring_buffer_poll_remote():
> > 			Update `struct ring_buffer` based on the remote
> > 			meta-page. Wake-up readers if necessary.
> > 
> > The kernel has to poll the meta-page to be notified of newly written
> > events.
> > 
> > 2. Tracefs
> > ----------
> > 
> > This series introduce a new trace_remote that does the link between
> > tracefs and the remote ring-buffer.
> > 
> > The interface is found in the remotes/ directory at the root of the
> > tracefs mount point. Each remote is like an instance and you'll find
> > there a subset of the regular Tracefs user-space interface:
> > 
> >   remotes/test/
> >      buffer_size_kb
> >      trace_clock
> >      trace_pipe
> >      trace
> >      per_cpu/
> >              cpuX/
> >                  trace
> >                  trace_pipe
> >      events/
> > 
> >             test/
> >                 selftest/
> >                           enable
> >                           id
> > 
> > Behind the scenes, kernel/trace/trace_remote.c creates this tracefs
> > hierarchy without relying on kernel/trace/trace.c. This is due to
> > fundamental differences:
> > 
> >   * Remote tracing doesn't support trace_array's system-specific
> >     features (snapshots, tracers, etc.).
> > 
> >   * Logged event formats differ (e.g., no PID for remote events).
> > 
> >   * Buffer operations require specific remote interactions.
> > 
> > 3. Simple Ring-Buffer
> > ---------------------
> > 
> > As the current ring-buffer.c implementation has too many dependencies to
> > be used directly by the pKVM hypervisor. A new simple implementation is
> > created and can be found in kernel/trace/simple-ring-buffer.c.
> > 
> > This implementation is write-only and is used by both the pKVM
> > hypervisor and a trace_remote test module.
> > 
> > 4. Events
> > ---------
> > 
> > A new REMOTE_EVENT() macro is added to simplify the creation of events
> > on the kernel side. As remote tracing buffer are read only, only the
> > event structure and a way of printing must be declared. The prototype of
> > the macro is very similar to the well-known TRACE_EVENT()
> > 
> >  REMOTE_EVENT(my_event, id,
> >      RE_STRUCT(
> >          re_field(u64, foobar)
> >      ),
> >      RE_PRINTK("foobar=%lld", __entry->foobar)
> >      )
> >   )
> > 
> > 5. pKVM
> > -------
> > 
> > The pKVM support simply creates a "hypervisor" trace_remote on the
> > kernel side and inherits from simple-ring-buffer.c on the hypervisor
> > side.
> > 
> > A new event macro is created HYP_EVENT() that is under the hood re-using
> > REMOTE_EVENT() (defined in the previous paragaph) as well as generate
> > hypervisor specific struct and trace_<event>() functions.
> > 
> > 5. Limitations:
> > ---------------
> > 
> > Non-consuming reading of the buffer isn't supported (i.e. cat trace ->
> > -EPERM) due to current the lack of support in the ring-buffer meta-page.
> > 
> > [1] https://tracingsummit.org/ts/2022/hypervisortracing/
> > [2] https://lore.kernel.org/all/20240510140435.3550353-1-vdonnefort@google.com/
> > 
> 
> BTW,  I tried to build this series and it fails.


Yes, appologies, I've started applying your comments today and I've figured out
I haven't tried building for x86.

I already have fixes locally for what's below.

I probably can send a v5 this week if you wish, unless you prefer to wait a bit
more for more comments?

> 
>   CALL    /work/git/test-linux.git/scripts/checksyscalls.sh
>   CC      kernel/trace/simple_ring_buffer.o
> In file included from ./arch/x86/include/generated/asm/rwonce.h:1,
>                  from /work/git/test-linux.git/include/linux/compiler.h:390,
>                  from /work/git/test-linux.git/arch/x86/include/asm/atomic.h:5,
>                  from /work/git/test-linux.git/include/linux/atomic.h:7,
>                  from /work/git/test-linux.git/kernel/trace/simple_ring_buffer.c:7:
> /work/git/test-linux.git/kernel/trace/simple_ring_buffer.c: In function ‘simple_rb_move_tail’:
> /work/git/test-linux.git/include/asm-generic/rwonce.h:55:37: error: assignment to ‘struct list_head *’ from ‘long unsigned int’ makes pointer from integer without a cast [-Wint-conversion]
>    55 |         *(volatile typeof(x) *)&(x) = (val);                            \
>       |                                     ^
> /work/git/test-linux.git/include/asm-generic/rwonce.h:61:9: note: in expansion of macro ‘__WRITE_ONCE’
>    61 |         __WRITE_ONCE(x, val);                                           \
>       |         ^~~~~~~~~~~~
> /work/git/test-linux.git/arch/x86/include/asm/barrier.h:63:9: note: in expansion of macro ‘WRITE_ONCE’
>    63 |         WRITE_ONCE(*p, v);                                              \
>       |         ^~~~~~~~~~
> /work/git/test-linux.git/include/asm-generic/barrier.h:172:55: note: in expansion of macro ‘__smp_store_release’
>   172 | #define smp_store_release(p, v) do { kcsan_release(); __smp_store_release(p, v); } while (0)
>       |                                                       ^~~~~~~~~~~~~~~~~~~
> /work/git/test-linux.git/kernel/trace/simple_ring_buffer.c:129:17: note: in expansion of macro ‘smp_store_release’
>   129 |                 smp_store_release(&new_tail->list.next,
>       |                 ^~~~~~~~~~~~~~~~~
> make[5]: *** [/work/git/test-linux.git/scripts/Makefile.build:203: kernel/trace/simple_ring_buffer.o] Error 1
> make[4]: *** [/work/git/test-linux.git/scripts/Makefile.build:461: kernel/trace] Error 2
> make[3]: *** [/work/git/test-linux.git/scripts/Makefile.build:461: kernel] Error 2
> make[2]: *** [/work/git/test-linux.git/Makefile:2004: .] Error 2
> make[1]: *** [/work/git/test-linux.git/Makefile:248: __sub-make] Error 2
> make[1]: Leaving directory '/work/build/trace/nobackup/debiantesting-x86-64'
> 
> Even when I fixed this, it then failed with the building of the sample module.
> 
> I think you need something like:
> 
> obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test_mod.o
> 
> remote_test_mod-y := simple_ring_buffer.o remote_test.o trace_remote.o
> 
> If the module needs more than one object file. Then the module should be
> called something that doesn't have a .c file and use that name with ".o" to
> add all the objects.
> 
> I think this could work, but this still had issues with functions not exported.
> 
> -- Steve

Re: [PATCH v4 00/24] Tracefs support for pKVM

[Steven Rostedt]

On Wed, 14 May 2025 19:13:37 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:

> I probably can send a v5 this week if you wish, unless you prefer to wait a bit
> more for more comments?

Feel free to send them this week, but I'll be on PTO starting tonight, so I
won't look at them until Tuesday.

-- Steve