[for-next][PATCH 00/18] ring-buffer: Add remote buffer infrastructure

[for-next][PATCH 00/18] ring-buffer: Add remote buffer infrastructure

[Steven Rostedt]

  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
ring-buffer/for-next

Head SHA1: a717943d8ecc0e533c581bf04473b50f6f17f2cb


Vincent Donnefort (18):
      ring-buffer: Add page statistics to the meta-page
      ring-buffer: Store bpage pointers into subbuf_ids
      ring-buffer: Introduce ring-buffer remotes
      ring-buffer: Add non-consuming read for ring-buffer remotes
      tracing: Introduce trace remotes
      tracing: Add reset to trace remotes
      tracing: Add non-consuming read 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: Export buffer_data_page and macros
      tracing: Introduce simple_ring_buffer
      tracing: Add a trace remote module for testing
      tracing: selftests: Add trace remote tests
      Documentation: tracing: Add tracing remotes
      tracing: load/unload page callbacks for simple_ring_buffer
      tracing: Check for undefined symbols in simple_ring_buffer

----
 Documentation/trace/index.rst                      |   11 +
 Documentation/trace/remotes.rst                    |   66 +
 fs/tracefs/inode.c                                 |    1 +
 include/linux/ring_buffer.h                        |   58 +
 include/linux/ring_buffer_types.h                  |   41 +
 include/linux/simple_ring_buffer.h                 |   65 +
 include/linux/trace_remote.h                       |   48 +
 include/linux/trace_remote_event.h                 |   33 +
 include/trace/define_remote_events.h               |   73 ++
 include/uapi/linux/trace_mmap.h                    |    8 +-
 kernel/trace/Kconfig                               |   14 +
 kernel/trace/Makefile                              |   20 +
 kernel/trace/remote_test.c                         |  261 ++++
 kernel/trace/remote_test_events.h                  |   10 +
 kernel/trace/ring_buffer.c                         |  354 ++++-
 kernel/trace/simple_ring_buffer.c                  |  517 ++++++++
 kernel/trace/trace.c                               |    4 +-
 kernel/trace/trace.h                               |    7 +
 kernel/trace/trace_remote.c                        | 1368 ++++++++++++++++++++
 .../selftests/ftrace/test.d/remotes/buffer_size.tc |   25 +
 .../selftests/ftrace/test.d/remotes/functions      |   88 ++
 .../selftests/ftrace/test.d/remotes/reset.tc       |   90 ++
 .../selftests/ftrace/test.d/remotes/trace.tc       |  127 ++
 .../selftests/ftrace/test.d/remotes/trace_pipe.tc  |  127 ++
 .../selftests/ftrace/test.d/remotes/unloading.tc   |   41 +
 25 files changed, 3400 insertions(+), 57 deletions(-)
 create mode 100644 Documentation/trace/remotes.rst
 create mode 100644 include/linux/ring_buffer_types.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/reset.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/trace.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

[for-next][PATCH 01/18] ring-buffer: Add page statistics to the meta-page

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

Add two fields pages_touched and pages_lost to the ring-buffer
meta-page. Those fields are useful to get the number of used pages in
the ring-buffer.

Link: https://patch.msgid.link/20260309162516.2623589-2-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/uapi/linux/trace_mmap.h | 8 ++++----
 kernel/trace/ring_buffer.c      | 2 ++
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
index c102ef35d11e..e8185889a1c8 100644
--- a/include/uapi/linux/trace_mmap.h
+++ b/include/uapi/linux/trace_mmap.h
@@ -17,8 +17,8 @@
  * @entries:		Number of entries in the ring-buffer.
  * @overrun:		Number of entries lost in the ring-buffer.
  * @read:		Number of entries that have been read.
- * @Reserved1:		Internal use only.
- * @Reserved2:		Internal use only.
+ * @pages_lost:		Number of pages overwritten by the writer.
+ * @pages_touched:	Number of pages written by the writer.
  */
 struct trace_buffer_meta {
 	__u32		meta_page_size;
@@ -39,8 +39,8 @@ struct trace_buffer_meta {
 	__u64	overrun;
 	__u64	read;
 
-	__u64	Reserved1;
-	__u64	Reserved2;
+	__u64	pages_lost;
+	__u64	pages_touched;
 };
 
 #define TRACE_MMAP_IOCTL_GET_READER		_IO('R', 0x20)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 17d0ea0cc3e6..82b4df579670 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -6154,6 +6154,8 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
 	meta->entries = local_read(&cpu_buffer->entries);
 	meta->overrun = local_read(&cpu_buffer->overrun);
 	meta->read = cpu_buffer->read;
+	meta->pages_lost = local_read(&cpu_buffer->pages_lost);
+	meta->pages_touched = local_read(&cpu_buffer->pages_touched);
 
 	/* Some archs do not have data cache coherency between kernel and user-space */
 	flush_kernel_vmap_range(cpu_buffer->meta_page, PAGE_SIZE);
-- 
2.51.0

[for-next][PATCH 02/18] ring-buffer: Store bpage pointers into subbuf_ids

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

The subbuf_ids field allows to point to a specific page from the
ring-buffer based on its ID. As a preparation or the upcoming
ring-buffer remote support, point this array to the buffer_page instead
of the buffer_data_page.

Link: https://patch.msgid.link/20260309162516.2623589-3-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 82b4df579670..3d2804a7e8ab 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -555,7 +555,7 @@ struct ring_buffer_per_cpu {
 	unsigned int			mapped;
 	unsigned int			user_mapped;	/* user space mapping */
 	struct mutex			mapping_lock;
-	unsigned long			*subbuf_ids;	/* ID to subbuf VA */
+	struct buffer_page		**subbuf_ids;	/* ID to subbuf VA */
 	struct trace_buffer_meta	*meta_page;
 	struct ring_buffer_cpu_meta	*ring_meta;
 
@@ -7036,7 +7036,7 @@ static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
 }
 
 static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
-				   unsigned long *subbuf_ids)
+				   struct buffer_page **subbuf_ids)
 {
 	struct trace_buffer_meta *meta = cpu_buffer->meta_page;
 	unsigned int nr_subbufs = cpu_buffer->nr_pages + 1;
@@ -7045,7 +7045,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
 	int id = 0;
 
 	id = rb_page_id(cpu_buffer, cpu_buffer->reader_page, id);
-	subbuf_ids[id++] = (unsigned long)cpu_buffer->reader_page->page;
+	subbuf_ids[id++] = cpu_buffer->reader_page;
 	cnt++;
 
 	first_subbuf = subbuf = rb_set_head_page(cpu_buffer);
@@ -7055,7 +7055,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
 		if (WARN_ON(id >= nr_subbufs))
 			break;
 
-		subbuf_ids[id] = (unsigned long)subbuf->page;
+		subbuf_ids[id] = subbuf;
 
 		rb_inc_page(&subbuf);
 		id++;
@@ -7064,7 +7064,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
 
 	WARN_ON(cnt != nr_subbufs);
 
-	/* install subbuf ID to kern VA translation */
+	/* install subbuf ID to bpage translation */
 	cpu_buffer->subbuf_ids = subbuf_ids;
 
 	meta->meta_struct_len = sizeof(*meta);
@@ -7220,13 +7220,15 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
 	}
 
 	while (p < nr_pages) {
+		struct buffer_page *subbuf;
 		struct page *page;
 		int off = 0;
 
 		if (WARN_ON_ONCE(s >= nr_subbufs))
 			return -EINVAL;
 
-		page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]);
+		subbuf = cpu_buffer->subbuf_ids[s];
+		page = virt_to_page((void *)subbuf->page);
 
 		for (; off < (1 << (subbuf_order)); off++, page++) {
 			if (p >= nr_pages)
@@ -7253,7 +7255,8 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 		    struct vm_area_struct *vma)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
-	unsigned long flags, *subbuf_ids;
+	struct buffer_page **subbuf_ids;
+	unsigned long flags;
 	int err;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
@@ -7277,7 +7280,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 	if (err)
 		return err;
 
-	/* subbuf_ids include the reader while nr_pages does not */
+	/* subbuf_ids includes the reader while nr_pages does not */
 	subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP_KERNEL);
 	if (!subbuf_ids) {
 		rb_free_meta_page(cpu_buffer);
-- 
2.51.0

[for-next][PATCH 03/18] ring-buffer: Introduce ring-buffer remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

Add ring-buffer remotes to support entities outside of the kernel (such
as firmware or a hypervisor) that writes events into a ring-buffer using
the tracefs format

Require a description of the ring-buffer pages (struct
trace_buffer_desc) and callbacks (swap_reader_page and reset) to set up
the ring-buffer on the kernel side.

Expect the remote entity to maintain and update the meta-page.

Link: https://patch.msgid.link/20260309162516.2623589-4-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/ring_buffer.h |  58 +++++++++
 kernel/trace/ring_buffer.c  | 233 ++++++++++++++++++++++++++++++++++--
 2 files changed, 283 insertions(+), 8 deletions(-)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index d862fa610270..994f52b34344 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -251,4 +251,62 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 void ring_buffer_map_dup(struct trace_buffer *buffer, int cpu);
 int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
 int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
+
+struct ring_buffer_desc {
+	int		cpu;
+	unsigned int	nr_page_va; /* excludes the meta page */
+	unsigned long	meta_va;
+	unsigned long	page_va[] __counted_by(nr_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 = max(DIV_ROUND_UP(buffer_size, PAGE_SIZE), 2UL) + 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_alloc_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 3d2804a7e8ab..88218377fa29 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -559,6 +559,8 @@ 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 */
@@ -581,6 +583,8 @@ struct trace_buffer {
 
 	struct ring_buffer_per_cpu	**buffers;
 
+	struct ring_buffer_remote	*remote;
+
 	struct hlist_node		node;
 	u64				(*clock)(void);
 
@@ -2238,6 +2242,40 @@ static void rb_meta_buffer_update(struct ring_buffer_per_cpu *cpu_buffer,
 	}
 }
 
+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,
 		long nr_pages, struct list_head *pages)
 {
@@ -2245,6 +2283,7 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	struct ring_buffer_cpu_meta *meta = NULL;
 	struct buffer_page *bpage, *tmp;
 	bool user_thread = current->mm != NULL;
+	struct ring_buffer_desc *desc = NULL;
 	long i;
 
 	/*
@@ -2273,6 +2312,12 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	if (buffer->range_addr_start)
 		meta = rb_range_meta(buffer, nr_pages, cpu_buffer->cpu);
 
+	if (buffer->remote) {
+		desc = ring_buffer_desc(buffer->remote->desc, cpu_buffer->cpu);
+		if (!desc || WARN_ON(desc->nr_page_va != (nr_pages + 1)))
+			return -EINVAL;
+	}
+
 	for (i = 0; i < nr_pages; i++) {
 
 		bpage = alloc_cpu_page(cpu_buffer->cpu);
@@ -2297,6 +2342,16 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 				rb_meta_buffer_update(cpu_buffer, bpage);
 			bpage->range = 1;
 			bpage->id = i + 1;
+		} else if (desc) {
+			void *p = ring_buffer_desc_page(desc, i + 1);
+
+			if (WARN_ON(!p))
+				goto free_pages;
+
+			bpage->page = p;
+			bpage->range = 1; /* bpage->page can't be freed */
+			bpage->id = i + 1;
+			cpu_buffer->subbuf_ids[i + 1] = bpage;
 		} else {
 			int order = cpu_buffer->buffer->subbuf_order;
 			bpage->page = alloc_cpu_data(cpu_buffer->cpu, order);
@@ -2394,6 +2449,30 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 		if (cpu_buffer->ring_meta->head_buffer)
 			rb_meta_buffer_update(cpu_buffer, bpage);
 		bpage->range = 1;
+	} else 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->nr_pages = nr_pages;
+		cpu_buffer->subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1,
+						 sizeof(*cpu_buffer->subbuf_ids), GFP_KERNEL);
+		if (!cpu_buffer->subbuf_ids)
+			goto fail_free_reader;
+
+		/* 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;
+
+		bpage->range = 1;
+		cpu_buffer->subbuf_ids[0] = bpage;
 	} else {
 		int order = cpu_buffer->buffer->subbuf_order;
 		bpage->page = alloc_cpu_data(cpu, order);
@@ -2453,6 +2532,9 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 
 	irq_work_sync(&cpu_buffer->irq_work.work);
 
+	if (cpu_buffer->remote)
+		kfree(cpu_buffer->subbuf_ids);
+
 	free_buffer_page(cpu_buffer->reader_page);
 
 	if (head) {
@@ -2475,7 +2557,8 @@ 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 __free(kfree) = NULL;
 	long nr_pages;
@@ -2515,6 +2598,8 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 	if (!buffer->buffers)
 		goto fail_free_cpumask;
 
+	cpu = raw_smp_processor_id();
+
 	/* If start/end are specified, then that overrides size */
 	if (start && end) {
 		unsigned long buffers_start;
@@ -2570,6 +2655,15 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 		buffer->range_addr_end = end;
 
 		rb_range_meta_init(buffer, nr_pages, scratch_size);
+	} else if (remote) {
+		struct ring_buffer_desc *desc = ring_buffer_desc(remote->desc, cpu);
+
+		buffer->remote = remote;
+		/* The writer is remote. This ring-buffer is read-only */
+		atomic_inc(&buffer->record_disabled);
+		nr_pages = desc->nr_page_va - 1;
+		if (nr_pages < 2)
+			goto fail_free_buffers;
 	} else {
 
 		/* need at least two pages */
@@ -2578,7 +2672,6 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 			nr_pages = 2;
 	}
 
-	cpu = raw_smp_processor_id();
 	cpumask_set_cpu(cpu, buffer->cpumask);
 	buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
 	if (!buffer->buffers[cpu])
@@ -2620,7 +2713,7 @@ 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);
@@ -2647,7 +2740,18 @@ 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)
@@ -5274,6 +5378,16 @@ unsigned long ring_buffer_overruns(struct trace_buffer *buffer)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_overruns);
 
+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(cpu_buffer->meta_page->pages_touched));
+	local_set(&cpu_buffer->pages_lost, READ_ONCE(cpu_buffer->meta_page->pages_lost));
+
+	return rb_num_of_entries(cpu_buffer);
+}
+
 static void rb_iter_reset(struct ring_buffer_iter *iter)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
@@ -5428,7 +5542,43 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
 }
 
 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)
+{
+	struct buffer_page *new_reader, *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->subbuf_ids[cpu_buffer->meta_page->reader.id];
+
+	WARN_ON_ONCE(cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu,
+							  cpu_buffer->remote->priv));
+	/* nr_pages doesn't include the reader page */
+	if (WARN_ON_ONCE(cpu_buffer->meta_page->reader.id > cpu_buffer->nr_pages))
+		return NULL;
+
+	new_reader = cpu_buffer->subbuf_ids[cpu_buffer->meta_page->reader.id];
+
+	WARN_ON_ONCE(prev_reader == new_reader);
+
+	cpu_buffer->reader_page->page = new_reader->page;
+	cpu_buffer->reader_page->id = new_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;
+
+	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);
@@ -5598,6 +5748,13 @@ 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;
@@ -5998,7 +6155,7 @@ ring_buffer_read_start(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_obj(*iter, flags);
@@ -6166,6 +6323,23 @@ 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
@@ -6396,6 +6570,46 @@ 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;
+
+	if (cpu != RING_BUFFER_ALL_CPUS) {
+		if (!cpumask_test_cpu(cpu, buffer->cpumask))
+			return -EINVAL;
+
+		cpu_buffer = buffer->buffers[cpu];
+
+		guard(raw_spinlock)(&cpu_buffer->reader_lock);
+		if (rb_read_remote_meta_page(cpu_buffer))
+			rb_wakeups(buffer, cpu_buffer);
+
+		return 0;
+	}
+
+	guard(cpus_read_lock)();
+
+	/*
+	 * 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];
+
+		guard(raw_spinlock)(&cpu_buffer->reader_lock);
+		rb_read_remote_meta_page(cpu_buffer);
+	}
+
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		if (rb_num_of_entries(cpu_buffer))
+			rb_wakeups(buffer, cpu_buffer);
+	}
+
+	return 0;
+}
+
 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
 /**
  * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
@@ -6634,6 +6848,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	unsigned int commit;
 	unsigned int read;
 	u64 save_timestamp;
+	bool force_memcpy;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return -1;
@@ -6671,6 +6886,8 @@ 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
@@ -6680,7 +6897,7 @@ 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;
@@ -7259,7 +7476,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 	unsigned long flags;
 	int err;
 
-	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+	if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->remote)
 		return -EINVAL;
 
 	cpu_buffer = buffer->buffers[cpu];
-- 
2.51.0

[for-next][PATCH 04/18] ring-buffer: Add non-consuming read for ring-buffer remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

Hopefully, the remote will only swap pages on the kernel instruction (via
the swap_reader_page() callback). This means we know at what point the
ring-buffer geometry has changed. It is therefore possible to rearrange
the kernel view of that ring-buffer to allow non-consuming read.

Link: https://patch.msgid.link/20260309162516.2623589-5-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 75 +++++++++++++++++++++++++++++++++++---
 1 file changed, 69 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 88218377fa29..fb39dd43e00b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -5388,10 +5388,51 @@ static bool rb_read_remote_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
 	return rb_num_of_entries(cpu_buffer);
 }
 
+static void rb_update_remote_head(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct buffer_page *next, *orig;
+	int retry = 3;
+
+	orig = next = cpu_buffer->head_page;
+	rb_inc_page(&next);
+
+	/* Run after the writer */
+	while (cpu_buffer->head_page->page->time_stamp > next->page->time_stamp) {
+		rb_inc_page(&next);
+
+		rb_list_head_clear(cpu_buffer->head_page->list.prev);
+		rb_inc_page(&cpu_buffer->head_page);
+		rb_set_list_to_head(cpu_buffer->head_page->list.prev);
+
+		if (cpu_buffer->head_page == orig) {
+			if (WARN_ON_ONCE(!(--retry)))
+				return;
+		}
+	}
+
+	orig = cpu_buffer->commit_page = cpu_buffer->head_page;
+	retry = 3;
+
+	while (cpu_buffer->commit_page->page->time_stamp < next->page->time_stamp) {
+		rb_inc_page(&next);
+		rb_inc_page(&cpu_buffer->commit_page);
+
+		if (cpu_buffer->commit_page == orig) {
+			if (WARN_ON_ONCE(!(--retry)))
+				return;
+		}
+	}
+}
+
 static void rb_iter_reset(struct ring_buffer_iter *iter)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
 
+	if (cpu_buffer->remote) {
+		rb_read_remote_meta_page(cpu_buffer);
+		rb_update_remote_head(cpu_buffer);
+	}
+
 	/* Iterator usage is expected to have record disabled */
 	iter->head_page = cpu_buffer->reader_page;
 	iter->head = cpu_buffer->reader_page->read;
@@ -5544,7 +5585,7 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
 static struct buffer_page *
 __rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer)
 {
-	struct buffer_page *new_reader, *prev_reader;
+	struct buffer_page *new_reader, *prev_reader, *prev_head, *new_head, *last;
 
 	if (!rb_read_remote_meta_page(cpu_buffer))
 		return NULL;
@@ -5568,10 +5609,32 @@ __rb_get_reader_page_from_remote(struct ring_buffer_per_cpu *cpu_buffer)
 
 	WARN_ON_ONCE(prev_reader == new_reader);
 
-	cpu_buffer->reader_page->page = new_reader->page;
-	cpu_buffer->reader_page->id = new_reader->id;
-	cpu_buffer->reader_page->read = 0;
-	cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
+	prev_head = new_reader;  /* New reader was also the previous head */
+	new_head = prev_head;
+	rb_inc_page(&new_head);
+	last = prev_head;
+	rb_dec_page(&last);
+
+	/* Clear the old HEAD flag */
+	rb_list_head_clear(cpu_buffer->head_page->list.prev);
+
+	prev_reader->list.next = prev_head->list.next;
+	prev_reader->list.prev = prev_head->list.prev;
+
+	/* Swap prev_reader with new_reader */
+	last->list.next = &prev_reader->list;
+	new_head->list.prev = &prev_reader->list;
+
+	new_reader->list.prev = &new_reader->list;
+	new_reader->list.next = &new_head->list;
+
+	/* Reactivate the HEAD flag */
+	rb_set_list_to_head(&last->list);
+
+	cpu_buffer->head_page = new_head;
+	cpu_buffer->reader_page = new_reader;
+	cpu_buffer->pages = &new_head->list;
+	cpu_buffer->read_stamp = new_reader->page->time_stamp;
 	cpu_buffer->lost_events = cpu_buffer->meta_page->reader.lost_events;
 
 	return rb_page_size(cpu_buffer->reader_page) ? cpu_buffer->reader_page : NULL;
@@ -6155,7 +6218,7 @@ ring_buffer_read_start(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) || buffer->remote)
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return NULL;
 
 	iter = kzalloc_obj(*iter, flags);
-- 
2.51.0

[for-next][PATCH 05/18] tracing: Introduce trace remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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.

Link: https://patch.msgid.link/20260309162516.2623589-6-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/trace_remote.h |  36 ++
 kernel/trace/Kconfig         |   3 +
 kernel/trace/Makefile        |   1 +
 kernel/trace/trace.c         |   2 +-
 kernel/trace/trace.h         |   6 +
 kernel/trace/trace_remote.c  | 619 +++++++++++++++++++++++++++++++++++
 6 files changed, 666 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/trace_remote.h
 create mode 100644 kernel/trace/trace_remote.c

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
new file mode 100644
index 000000000000..65b7e7b8267c
--- /dev/null
+++ b/include/linux/trace_remote.h
@@ -0,0 +1,36 @@
+/* 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 - Callbacks used by Tracefs to control the remote
+ * @load_trace_buffer:  Called before Tracefs accesses the trace buffer for the first
+ *			time. Must return a &trace_buffer_desc
+ *			(most likely filled with trace_remote_alloc_buffer())
+ * @unload_trace_buffer:
+ *			Called once Tracefs has no use for the trace buffer
+ *			(most likely call trace_remote_free_buffer())
+ * @enable_tracing:	Called on Tracefs tracing_on. It is expected from the
+ *			remote to allow writing.
+ * @swap_reader_page:	Called when Tracefs consumes a new page from a
+ *			ring-buffer. It is expected from the remote to isolate a
+ *			new reader-page from the @cpu ring-buffer.
+ */
+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 desc_size, size_t buffer_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 49de13cae428..384dd36c8e29 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -1281,4 +1281,7 @@ 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 04096c21d06b..318923ce39f5 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -128,4 +128,5 @@ 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 ebd996f8710e..e33cb3c39f6e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8589,7 +8589,7 @@ 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 b8f3804586a0..d6af4405b341 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -689,6 +689,12 @@ 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);
 
 
 /**
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
new file mode 100644
index 000000000000..8b06f730376e
--- /dev/null
+++ b/kernel/trace/trace_remote.c
@@ -0,0 +1,619 @@
+// 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 int trace_remote_load(struct trace_remote *remote)
+{
+	struct ring_buffer_remote *rb_remote = &remote->rb_remote;
+	struct trace_buffer_desc *desc;
+
+	lockdep_assert_held(&remote->lock);
+
+	if (trace_remote_loaded(remote))
+		return 0;
+
+	desc = remote->cbs->load_trace_buffer(remote->trace_buffer_size, remote->priv);
+	if (IS_ERR(desc))
+		return PTR_ERR(desc);
+
+	rb_remote->desc = desc;
+	rb_remote->swap_reader_page = remote->cbs->swap_reader_page;
+	rb_remote->priv = remote->priv;
+	remote->trace_buffer = ring_buffer_alloc_remote(rb_remote);
+	if (!remote->trace_buffer) {
+		remote->cbs->unload_trace_buffer(desc, remote->priv);
+		return -ENOMEM;
+	}
+
+	remote->trace_buffer_desc = desc;
+
+	return 0;
+}
+
+static void trace_remote_try_unload(struct trace_remote *remote)
+{
+	lockdep_assert_held(&remote->lock);
+
+	if (!trace_remote_loaded(remote))
+		return;
+
+	/* The buffer is being read or writable */
+	if (remote->nr_readers || remote->tracing_on)
+		return;
+
+	/* The buffer has readable data */
+	if (!ring_buffer_empty(remote->trace_buffer))
+		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_enable_tracing(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_try_unload(remote);
+		return ret;
+	}
+
+	remote->tracing_on = true;
+
+	return 0;
+}
+
+static int trace_remote_disable_tracing(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_try_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_enable_tracing(remote) : trace_remote_disable_tracing(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);
+
+	if (trace_remote_loaded(remote))
+		return -EBUSY;
+
+	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 int trace_remote_get(struct trace_remote *remote, int cpu)
+{
+	int ret;
+
+	if (remote->nr_readers == UINT_MAX)
+		return -EBUSY;
+
+	ret = trace_remote_load(remote);
+	if (ret)
+		return ret;
+
+	remote->nr_readers++;
+
+	return 0;
+}
+
+static void trace_remote_put(struct trace_remote *remote)
+{
+	if (WARN_ON(!remote->nr_readers))
+		return;
+
+	remote->nr_readers--;
+	if (remote->nr_readers)
+		return;
+
+	trace_remote_try_unload(remote);
+}
+
+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 = NULL;
+	int ret;
+
+	lockdep_assert_held(&remote->lock);
+
+
+	ret = trace_remote_get(remote, cpu);
+	if (ret)
+		return ERR_PTR(ret);
+
+	/* Test the CPU */
+	ret = ring_buffer_poll_remote(remote->trace_buffer, cpu);
+	if (ret)
+		goto err;
+
+	iter = kzalloc_obj(*iter);
+	if (iter) {
+		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:
+	kfree(iter);
+	trace_remote_put(remote);
+
+	return ERR_PTR(ret);
+}
+
+static void trace_remote_iter_free(struct trace_remote_iterator *iter)
+{
+	struct trace_remote *remote;
+
+	if (!iter)
+		return;
+
+	remote = iter->remote;
+
+	lockdep_assert_held(&remote->lock);
+
+	kfree(iter);
+	trace_remote_put(remote);
+}
+
+static bool trace_remote_iter_read_event(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_event(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);
+
+	trace_remote_iter_free(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_read_event(iter)) {
+		int prev_len = iter->seq.seq.len;
+
+		if (trace_remote_iter_print_event(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, *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");
+			return -ENOMEM;
+		}
+		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;
+	}
+
+	d = trace_create_file("tracing_on", TRACEFS_MODE_WRITE, remote_d, remote, &tracing_on_fops);
+	if (!d)
+		goto err;
+
+	d = trace_create_file("buffer_size_kb", TRACEFS_MODE_WRITE, remote_d, remote,
+			      &buffer_size_kb_fops);
+	if (!d)
+		goto err;
+
+	d = trace_create_file("trace_pipe", TRACEFS_MODE_READ, remote_d, remote, &trace_pipe_fops);
+	if (!d)
+		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;
+		}
+
+		d = trace_create_cpu_file("trace_pipe", TRACEFS_MODE_READ, cpu_d, remote, cpu,
+					  &trace_pipe_fops);
+		if (!d)
+			goto err;
+	}
+
+	return 0;
+
+err:
+	if (root_inited) {
+		tracefs_remove(root);
+		root = NULL;
+	} else {
+		tracefs_remove(remote_d);
+	}
+
+	return -ENOMEM;
+}
+
+/**
+ * trace_remote_register() - Register a Tracefs remote
+ * @name:	Name of the remote, used for the Tracefs remotes/ directory.
+ * @cbs:	Set of callbacks used to control the remote.
+ * @priv:	Private data, passed to each callback from @cbs.
+ * @events:	Array of events. &remote_event.name and &remote_event.id must be
+ *		filled by the caller.
+ * @nr_events:	Number of events in the @events array.
+ *
+ * A trace remote is an entity, outside of the kernel (most likely firmware or
+ * hypervisor) capable of writing events into a Tracefs compatible ring-buffer.
+ * The kernel would then act as a reader.
+ *
+ * The registered remote will be found under the Tracefs directory
+ * remotes/<name>.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv)
+{
+	struct trace_remote *remote;
+
+	remote = kzalloc_obj(*remote);
+	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;
+}
+EXPORT_SYMBOL_GPL(trace_remote_register);
+
+/**
+ * trace_remote_free_buffer() - Free trace buffer allocated with trace_remote_alloc_buffer()
+ * @desc:	Descriptor of the per-CPU ring-buffers, originally filled by
+ *		trace_remote_alloc_buffer()
+ *
+ * Most likely called from &trace_remote_callbacks.unload_trace_buffer.
+ */
+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]);
+	}
+}
+EXPORT_SYMBOL_GPL(trace_remote_free_buffer);
+
+/**
+ * trace_remote_alloc_buffer() - Dynamically allocate a trace buffer
+ * @desc:		Uninitialized trace_buffer_desc
+ * @desc_size:		Size of the trace_buffer_desc. Must be at least equal to
+ *			trace_buffer_desc_size()
+ * @buffer_size:	Size in bytes of each per-CPU ring-buffer
+ * @cpumask:		CPUs to allocate a ring-buffer for
+ *
+ * Helper to dynamically allocate a set of pages (enough to cover @buffer_size)
+ * for each CPU from @cpumask and fill @desc. Most likely called from
+ * &trace_remote_callbacks.load_trace_buffer.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_size, size_t buffer_size,
+			      const struct cpumask *cpumask)
+{
+	unsigned int nr_pages = max(DIV_ROUND_UP(buffer_size, PAGE_SIZE), 2UL) + 1;
+	void *desc_end = desc + desc_size;
+	struct ring_buffer_desc *rb_desc;
+	int cpu, ret = -ENOMEM;
+
+	if (desc_size < struct_size(desc, __data, 0))
+		return -EINVAL;
+
+	desc->nr_cpus = 0;
+	desc->struct_len = struct_size(desc, __data, 0);
+
+	rb_desc = (struct ring_buffer_desc *)&desc->__data[0];
+
+	for_each_cpu(cpu, cpumask) {
+		unsigned int id;
+
+		if ((void *)rb_desc + struct_size(rb_desc, page_va, nr_pages) > desc_end) {
+			ret = -EINVAL;
+			goto err;
+		}
+
+		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 += struct_size(rb_desc, page_va, rb_desc->nr_page_va);
+		rb_desc = __next_ring_buffer_desc(rb_desc);
+	}
+
+	return 0;
+
+err:
+	trace_remote_free_buffer(desc);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(trace_remote_alloc_buffer);
-- 
2.51.0

[for-next][PATCH 06/18] tracing: Add reset to trace remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

Allow to reset the trace remote buffer by writing to the Tracefs "trace"
file. This is similar to the regular Tracefs interface.

Link: https://patch.msgid.link/20260309162516.2623589-7-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/trace_remote.h |  3 +++
 kernel/trace/trace_remote.c  | 45 ++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
index 65b7e7b8267c..10ca03dc192b 100644
--- a/include/linux/trace_remote.h
+++ b/include/linux/trace_remote.h
@@ -17,6 +17,8 @@
  *			remote to allow writing.
  * @swap_reader_page:	Called when Tracefs consumes a new page from a
  *			ring-buffer. It is expected from the remote to isolate a
+ * @reset:		Called on `echo 0 > trace`. It is expected from the
+ *			remote to reset all ring-buffer pages.
  *			new reader-page from the @cpu ring-buffer.
  */
 struct trace_remote_callbacks {
@@ -24,6 +26,7 @@ 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 8b06f730376e..a7b94736dd38 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -63,6 +63,7 @@ static int trace_remote_load(struct trace_remote *remote)
 	rb_remote->desc = 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_alloc_remote(rb_remote);
 	if (!remote->trace_buffer) {
 		remote->cbs->unload_trace_buffer(desc, remote->priv);
@@ -138,6 +139,21 @@ static int trace_remote_disable_tracing(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);
+
+	trace_remote_try_unload(remote);
+}
+
 static ssize_t
 tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
 {
@@ -414,6 +430,26 @@ 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, *d;
@@ -452,6 +488,10 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 	if (!d)
 		goto err;
 
+	d = trace_create_file("trace", TRACEFS_MODE_WRITE, remote_d, remote, &trace_fops);
+	if (!d)
+		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);
@@ -474,6 +514,11 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 					  &trace_pipe_fops);
 		if (!d)
 			goto err;
+
+		d = trace_create_cpu_file("trace", TRACEFS_MODE_WRITE, cpu_d, remote, cpu,
+					  &trace_fops);
+		if (!d)
+			goto err;
 	}
 
 	return 0;
-- 
2.51.0

[for-next][PATCH 07/18] tracing: Add non-consuming read to trace remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

Allow reading the trace file for trace remotes. This performs a
non-consuming read of the trace buffer.

Link: https://patch.msgid.link/20260309162516.2623589-8-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c        |   2 +-
 kernel/trace/trace.h        |   1 +
 kernel/trace/trace_remote.c | 339 ++++++++++++++++++++++++++++++++++--
 3 files changed, 326 insertions(+), 16 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e33cb3c39f6e..5e1129b011cb 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3856,7 +3856,7 @@ static int s_show(struct seq_file *m, void *v)
  * Should be used after trace_array_get(), trace_types_lock
  * ensures that i_cdev was already initialized.
  */
-static inline int tracing_get_cpu(struct inode *inode)
+int tracing_get_cpu(struct inode *inode)
 {
 	if (inode->i_cdev) /* See trace_create_cpu_file() */
 		return (long)inode->i_cdev - 1;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index d6af4405b341..fbbd0b2ee76f 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -695,6 +695,7 @@ struct dentry *trace_create_cpu_file(const char *name,
 				     void *data,
 				     long cpu,
 				     const struct file_operations *fops);
+int tracing_get_cpu(struct inode *inode);
 
 
 /**
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index a7b94736dd38..039ba71c3b3e 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -18,14 +18,23 @@
 #define TRACEFS_MODE_WRITE	0640
 #define TRACEFS_MODE_READ	0440
 
+enum tri_type {
+	TRI_CONSUMING,
+	TRI_NONCONSUMING,
+};
+
 struct trace_remote_iterator {
 	struct trace_remote		*remote;
 	struct trace_seq		seq;
 	struct delayed_work		poll_work;
 	unsigned long			lost_events;
 	u64				ts;
+	struct ring_buffer_iter		*rb_iter;
+	struct ring_buffer_iter		**rb_iters;
 	int				cpu;
 	int				evt_cpu;
+	loff_t				pos;
+	enum tri_type			type;
 };
 
 struct trace_remote {
@@ -36,6 +45,8 @@ struct trace_remote {
 	unsigned long			trace_buffer_size;
 	struct ring_buffer_remote	rb_remote;
 	struct mutex			lock;
+	struct rw_semaphore		reader_lock;
+	struct rw_semaphore		*pcpu_reader_locks;
 	unsigned int			nr_readers;
 	unsigned int			poll_ms;
 	bool				tracing_on;
@@ -230,6 +241,20 @@ static int trace_remote_get(struct trace_remote *remote, int cpu)
 	if (ret)
 		return ret;
 
+	if (cpu != RING_BUFFER_ALL_CPUS && !remote->pcpu_reader_locks) {
+		int lock_cpu;
+
+		remote->pcpu_reader_locks = kcalloc(nr_cpu_ids, sizeof(*remote->pcpu_reader_locks),
+						    GFP_KERNEL);
+		if (!remote->pcpu_reader_locks) {
+			trace_remote_try_unload(remote);
+			return -ENOMEM;
+		}
+
+		for_each_possible_cpu(lock_cpu)
+			init_rwsem(&remote->pcpu_reader_locks[lock_cpu]);
+	}
+
 	remote->nr_readers++;
 
 	return 0;
@@ -244,6 +269,9 @@ static void trace_remote_put(struct trace_remote *remote)
 	if (remote->nr_readers)
 		return;
 
+	kfree(remote->pcpu_reader_locks);
+	remote->pcpu_reader_locks = NULL;
+
 	trace_remote_try_unload(remote);
 }
 
@@ -258,13 +286,55 @@ static void __poll_remote(struct work_struct *work)
 			      msecs_to_jiffies(iter->remote->poll_ms));
 }
 
-static struct trace_remote_iterator *trace_remote_iter(struct trace_remote *remote, int cpu)
+static void __free_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu)
+{
+	if (cpu != RING_BUFFER_ALL_CPUS) {
+		ring_buffer_read_finish(iter->rb_iter);
+		return;
+	}
+
+	for_each_possible_cpu(cpu) {
+		if (iter->rb_iters[cpu])
+			ring_buffer_read_finish(iter->rb_iters[cpu]);
+	}
+
+	kfree(iter->rb_iters);
+}
+
+static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu)
+{
+	if (cpu != RING_BUFFER_ALL_CPUS) {
+		iter->rb_iter = ring_buffer_read_start(iter->remote->trace_buffer, cpu, GFP_KERNEL);
+
+		return iter->rb_iter ? 0 : -ENOMEM;
+	}
+
+	iter->rb_iters = kcalloc(nr_cpu_ids, sizeof(*iter->rb_iters), GFP_KERNEL);
+	if (!iter->rb_iters)
+		return -ENOMEM;
+
+	for_each_possible_cpu(cpu) {
+		iter->rb_iters[cpu] = ring_buffer_read_start(iter->remote->trace_buffer, cpu,
+							     GFP_KERNEL);
+		if (!iter->rb_iters[cpu]) {
+			__free_ring_buffer_iter(iter, RING_BUFFER_ALL_CPUS);
+			return -ENOMEM;
+		}
+	}
+
+	return 0;
+}
+
+static struct trace_remote_iterator
+*trace_remote_iter(struct trace_remote *remote, int cpu, enum tri_type type)
 {
 	struct trace_remote_iterator *iter = NULL;
 	int ret;
 
 	lockdep_assert_held(&remote->lock);
 
+	if (type == TRI_NONCONSUMING && !trace_remote_loaded(remote))
+		return NULL;
 
 	ret = trace_remote_get(remote, cpu);
 	if (ret)
@@ -279,9 +349,21 @@ static struct trace_remote_iterator *trace_remote_iter(struct trace_remote *remo
 	if (iter) {
 		iter->remote = remote;
 		iter->cpu = cpu;
+		iter->type = type;
 		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));
+
+		switch (type) {
+		case TRI_CONSUMING:
+			INIT_DELAYED_WORK(&iter->poll_work, __poll_remote);
+			schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_ms));
+			break;
+		case TRI_NONCONSUMING:
+			ret = __alloc_ring_buffer_iter(iter, cpu);
+			break;
+		}
+
+		if (ret)
+			goto err;
 
 		return iter;
 	}
@@ -305,10 +387,100 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter)
 
 	lockdep_assert_held(&remote->lock);
 
+	switch (iter->type) {
+	case TRI_CONSUMING:
+		cancel_delayed_work_sync(&iter->poll_work);
+		break;
+	case TRI_NONCONSUMING:
+		__free_ring_buffer_iter(iter, iter->cpu);
+		break;
+	}
+
 	kfree(iter);
 	trace_remote_put(remote);
 }
 
+static void trace_remote_iter_read_start(struct trace_remote_iterator *iter)
+{
+	struct trace_remote *remote = iter->remote;
+	int cpu = iter->cpu;
+
+	/* Acquire global reader lock */
+	if (cpu == RING_BUFFER_ALL_CPUS && iter->type == TRI_CONSUMING)
+		down_write(&remote->reader_lock);
+	else
+		down_read(&remote->reader_lock);
+
+	if (cpu == RING_BUFFER_ALL_CPUS)
+		return;
+
+	/*
+	 * No need for the remote lock here, iter holds a reference on
+	 * remote->nr_readers
+	 */
+
+	/* Get the per-CPU one */
+	if (WARN_ON_ONCE(!remote->pcpu_reader_locks))
+		return;
+
+	if (iter->type == TRI_CONSUMING)
+		down_write(&remote->pcpu_reader_locks[cpu]);
+	else
+		down_read(&remote->pcpu_reader_locks[cpu]);
+}
+
+static void trace_remote_iter_read_finished(struct trace_remote_iterator *iter)
+{
+	struct trace_remote *remote = iter->remote;
+	int cpu = iter->cpu;
+
+	/* Release per-CPU reader lock */
+	if (cpu != RING_BUFFER_ALL_CPUS) {
+		/*
+		 * No need for the remote lock here, iter holds a reference on
+		 * remote->nr_readers
+		 */
+		if (iter->type == TRI_CONSUMING)
+			up_write(&remote->pcpu_reader_locks[cpu]);
+		else
+			up_read(&remote->pcpu_reader_locks[cpu]);
+	}
+
+	/* Release global reader lock */
+	if (cpu == RING_BUFFER_ALL_CPUS && iter->type == TRI_CONSUMING)
+		up_write(&remote->reader_lock);
+	else
+		up_read(&remote->reader_lock);
+}
+
+static struct ring_buffer_iter *__get_rb_iter(struct trace_remote_iterator *iter, int cpu)
+{
+	return iter->cpu != RING_BUFFER_ALL_CPUS ? iter->rb_iter : iter->rb_iters[cpu];
+}
+
+static struct ring_buffer_event *
+__peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long *lost_events)
+{
+	struct ring_buffer_event *rb_evt;
+	struct ring_buffer_iter *rb_iter;
+
+	switch (iter->type) {
+	case TRI_CONSUMING:
+		return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events);
+	case TRI_NONCONSUMING:
+		rb_iter = __get_rb_iter(iter, cpu);
+		rb_evt = ring_buffer_iter_peek(rb_iter, ts);
+		if (!rb_evt)
+			return NULL;
+
+		*lost_events = ring_buffer_iter_dropped(rb_iter);
+
+		return rb_evt;
+	}
+
+	return NULL;
+}
+
 static bool trace_remote_iter_read_event(struct trace_remote_iterator *iter)
 {
 	struct trace_buffer *trace_buffer = iter->remote->trace_buffer;
@@ -318,7 +490,7 @@ static bool trace_remote_iter_read_event(struct trace_remote_iterator *iter)
 		if (ring_buffer_empty_cpu(trace_buffer, cpu))
 			return false;
 
-		if (!ring_buffer_peek(trace_buffer, cpu, &iter->ts, &iter->lost_events))
+		if (!__peek_event(iter, cpu, &iter->ts, &iter->lost_events))
 			return false;
 
 		iter->evt_cpu = cpu;
@@ -333,7 +505,7 @@ static bool trace_remote_iter_read_event(struct trace_remote_iterator *iter)
 		if (ring_buffer_empty_cpu(trace_buffer, cpu))
 			continue;
 
-		if (!ring_buffer_peek(trace_buffer, cpu, &ts, &lost_events))
+		if (!__peek_event(iter, cpu, &ts, &lost_events))
 			continue;
 
 		if (ts >= iter->ts)
@@ -347,6 +519,20 @@ static bool trace_remote_iter_read_event(struct trace_remote_iterator *iter)
 	return iter->ts != U64_MAX;
 }
 
+static void trace_remote_iter_move(struct trace_remote_iterator *iter)
+{
+	struct trace_buffer *trace_buffer = iter->remote->trace_buffer;
+
+	switch (iter->type) {
+	case TRI_CONSUMING:
+		ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL);
+		break;
+	case TRI_NONCONSUMING:
+		ring_buffer_iter_advance(__get_rb_iter(iter, iter->evt_cpu));
+		break;
+	}
+}
+
 static int trace_remote_iter_print_event(struct trace_remote_iterator *iter)
 {
 	unsigned long usecs_rem;
@@ -369,13 +555,14 @@ 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;
+	int cpu = tracing_get_cpu(inode);
 
 	guard(mutex)(&remote->lock);
-	iter = trace_remote_iter(remote, cpu);
+
+	iter = trace_remote_iter(remote, cpu, TRI_CONSUMING);
+	if (IS_ERR(iter))
+		return PTR_ERR(iter);
+
 	filp->private_data = iter;
 
 	return IS_ERR(iter) ? PTR_ERR(iter) : 0;
@@ -410,6 +597,8 @@ static ssize_t trace_pipe_read(struct file *filp, char __user *ubuf, size_t cnt,
 	if (ret < 0)
 		return ret;
 
+	trace_remote_iter_read_start(iter);
+
 	while (trace_remote_iter_read_event(iter)) {
 		int prev_len = iter->seq.seq.len;
 
@@ -418,9 +607,11 @@ static ssize_t trace_pipe_read(struct file *filp, char __user *ubuf, size_t cnt,
 			break;
 		}
 
-		ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL);
+		trace_remote_iter_move(iter);
 	}
 
+	trace_remote_iter_read_finished(iter);
+
 	goto copy_to_user;
 }
 
@@ -430,14 +621,127 @@ static const struct file_operations trace_pipe_fops = {
 	.release	= trace_pipe_release,
 };
 
+static void *trace_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct trace_remote_iterator *iter = m->private;
+
+	++*pos;
+
+	if (!iter || !trace_remote_iter_read_event(iter))
+		return NULL;
+
+	trace_remote_iter_move(iter);
+	iter->pos++;
+
+	return iter;
+}
+
+static void *trace_start(struct seq_file *m, loff_t *pos)
+{
+	struct trace_remote_iterator *iter = m->private;
+	loff_t i;
+
+	if (!iter)
+		return NULL;
+
+	trace_remote_iter_read_start(iter);
+
+	if (!*pos) {
+		iter->pos = -1;
+		return trace_next(m, NULL, &i);
+	}
+
+	i = iter->pos;
+	while (i < *pos) {
+		iter = trace_next(m, NULL, &i);
+		if (!iter)
+			return NULL;
+	}
+
+	return iter;
+}
+
+static int trace_show(struct seq_file *m, void *v)
+{
+	struct trace_remote_iterator *iter = v;
+
+	trace_seq_init(&iter->seq);
+
+	if (trace_remote_iter_print_event(iter)) {
+		seq_printf(m, "[EVENT %d PRINT TOO BIG]\n", iter->evt->id);
+		return 0;
+	}
+
+	return trace_print_seq(m, &iter->seq);
+}
+
+static void trace_stop(struct seq_file *m, void *v)
+{
+	struct trace_remote_iterator *iter = m->private;
+
+	if (iter)
+		trace_remote_iter_read_finished(iter);
+}
+
+static const struct seq_operations trace_sops = {
+	.start		= trace_start,
+	.next		= trace_next,
+	.show		= trace_show,
+	.stop		= trace_stop,
+};
+
+static int trace_open(struct inode *inode, struct file *filp)
+{
+	struct trace_remote *remote = inode->i_private;
+	struct trace_remote_iterator *iter = NULL;
+	int cpu = tracing_get_cpu(inode);
+	int ret;
+
+	if (!(filp->f_mode & FMODE_READ))
+		return 0;
+
+	guard(mutex)(&remote->lock);
+
+	iter = trace_remote_iter(remote, cpu, TRI_NONCONSUMING);
+	if (IS_ERR(iter))
+		return PTR_ERR(iter);
+
+	ret = seq_open(filp, &trace_sops);
+	if (ret) {
+		trace_remote_iter_free(iter);
+		return ret;
+	}
+
+	((struct seq_file *)filp->private_data)->private = (void *)iter;
+
+	return 0;
+}
+
+static int trace_release(struct inode *inode, struct file *filp)
+{
+	struct trace_remote_iterator *iter;
+
+	if (!(filp->f_mode & FMODE_READ))
+		return 0;
+
+	iter = ((struct seq_file *)filp->private_data)->private;
+	seq_release(inode, filp);
+
+	if (!iter)
+		return 0;
+
+	guard(mutex)(&iter->remote->lock);
+
+	trace_remote_iter_free(iter);
+
+	return 0;
+}
+
 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;
+	int cpu = tracing_get_cpu(inode);
 
 	guard(mutex)(&remote->lock);
 
@@ -447,7 +751,11 @@ static ssize_t trace_write(struct file *filp, const char __user *ubuf, size_t cn
 }
 
 static const struct file_operations trace_fops = {
+	.open		= trace_open,
 	.write		= trace_write,
+	.read		= seq_read,
+	.read_iter	= seq_read_iter,
+	.release	= trace_release,
 };
 
 static int trace_remote_init_tracefs(const char *name, struct trace_remote *remote)
@@ -565,6 +873,7 @@ int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs,
 	remote->trace_buffer_size = 7 << 10;
 	remote->poll_ms = 100;
 	mutex_init(&remote->lock);
+	init_rwsem(&remote->reader_lock);
 
 	if (trace_remote_init_tracefs(name, remote)) {
 		kfree(remote);
-- 
2.51.0

[for-next][PATCH 08/18] tracing: Add init callback to trace remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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

Link: https://patch.msgid.link/20260309162516.2623589-9-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/trace_remote.h | 4 ++++
 kernel/trace/trace_remote.c  | 7 ++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
index 10ca03dc192b..090c58b7d92b 100644
--- a/include/linux/trace_remote.h
+++ b/include/linux/trace_remote.h
@@ -3,10 +3,13 @@
 #ifndef _LINUX_TRACE_REMOTE_H
 #define _LINUX_TRACE_REMOTE_H
 
+#include <linux/dcache.h>
 #include <linux/ring_buffer.h>
 
 /**
  * struct trace_remote_callbacks - Callbacks used by Tracefs to control the remote
+ * @init:		Called once the remote has been registered. Allows the
+ *			caller to extend the Tracefs remote directory
  * @load_trace_buffer:  Called before Tracefs accesses the trace buffer for the first
  *			time. Must return a &trace_buffer_desc
  *			(most likely filled with trace_remote_alloc_buffer())
@@ -22,6 +25,7 @@
  *			new reader-page from the @cpu ring-buffer.
  */
 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);
 	int	(*enable_tracing)(bool enable, void *priv);
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 039ba71c3b3e..294d051dcef1 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -863,6 +863,7 @@ 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_obj(*remote);
 	if (!remote)
@@ -880,7 +881,11 @@ 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;
 }
 EXPORT_SYMBOL_GPL(trace_remote_register);
 
-- 
2.51.0

[for-next][PATCH 09/18] tracing: Add events to trace remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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.

Link: https://patch.msgid.link/20260309162516.2623589-10-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/trace_remote.h       |   7 +-
 include/linux/trace_remote_event.h |  23 +++
 kernel/trace/trace_remote.c        | 264 ++++++++++++++++++++++++++++-
 3 files changed, 288 insertions(+), 6 deletions(-)
 create mode 100644 include/linux/trace_remote_event.h

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
index 090c58b7d92b..fcd1d46ea466 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 - Callbacks used by Tracefs to control the remote
@@ -23,6 +24,8 @@
  * @reset:		Called on `echo 0 > trace`. It is expected from the
  *			remote to reset all ring-buffer pages.
  *			new reader-page from the @cpu ring-buffer.
+ * @enable_event:	Called on events/event_name/enable. It is expected from
+ *			the remote to allow the writing event @id.
  */
 struct trace_remote_callbacks {
 	int	(*init)(struct dentry *d, void *priv);
@@ -31,9 +34,11 @@ 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 desc_size, size_t buffer_size,
 			      const struct cpumask *cpumask);
diff --git a/include/linux/trace_remote_event.h b/include/linux/trace_remote_event.h
new file mode 100644
index 000000000000..a4449008a075
--- /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 30
+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 294d051dcef1..0d0af53c0ce9 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -31,6 +31,7 @@ struct trace_remote_iterator {
 	u64				ts;
 	struct ring_buffer_iter		*rb_iter;
 	struct ring_buffer_iter		**rb_iters;
+	struct remote_event_hdr		*evt;
 	int				cpu;
 	int				evt_cpu;
 	loff_t				pos;
@@ -42,6 +43,10 @@ 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;
@@ -168,7 +173,8 @@ 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;
 
@@ -197,7 +203,8 @@ 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;
 
@@ -484,16 +491,19 @@ __peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long
 static bool trace_remote_iter_read_event(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 (!__peek_event(iter, cpu, &iter->ts, &iter->lost_events))
+		rb_evt = __peek_event(iter, cpu, &iter->ts, &iter->lost_events);
+		if (!rb_evt)
 			return false;
 
 		iter->evt_cpu = cpu;
+		iter->evt = ring_buffer_event_data(rb_evt);
 		return true;
 	}
 
@@ -505,7 +515,8 @@ static bool trace_remote_iter_read_event(struct trace_remote_iterator *iter)
 		if (ring_buffer_empty_cpu(trace_buffer, cpu))
 			continue;
 
-		if (!__peek_event(iter, cpu, &ts, &lost_events))
+		rb_evt = __peek_event(iter, cpu, &ts, &lost_events);
+		if (!rb_evt)
 			continue;
 
 		if (ts >= iter->ts)
@@ -513,6 +524,7 @@ static bool trace_remote_iter_read_event(struct trace_remote_iterator *iter)
 
 		iter->ts = ts;
 		iter->evt_cpu = cpu;
+		iter->evt = ring_buffer_event_data(rb_evt);
 		iter->lost_events = lost_events;
 	}
 
@@ -533,8 +545,11 @@ static void trace_remote_iter_move(struct trace_remote_iterator *iter)
 	}
 }
 
+static struct remote_event *trace_remote_find_event(struct trace_remote *remote, unsigned short id);
+
 static int trace_remote_iter_print_event(struct trace_remote_iterator *iter)
 {
+	struct remote_event *evt;
 	unsigned long usecs_rem;
 	u64 ts = iter->ts;
 
@@ -548,6 +563,12 @@ static int trace_remote_iter_print_event(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;
 }
 
@@ -829,6 +850,8 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 			goto err;
 	}
 
+	remote->dentry = remote_d;
+
 	return 0;
 
 err:
@@ -842,6 +865,9 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
 	return -ENOMEM;
 }
 
+static int trace_remote_register_events(const char *remote_name, struct trace_remote *remote,
+					struct remote_event *events, size_t nr_events);
+
 /**
  * trace_remote_register() - Register a Tracefs remote
  * @name:	Name of the remote, used for the Tracefs remotes/ directory.
@@ -860,7 +886,8 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo
  *
  * Return: 0 on success, negative error code on failure.
  */
-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)
 {
 	struct trace_remote *remote;
 	int ret;
@@ -881,6 +908,13 @@ 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);
@@ -976,3 +1010,223 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_size,
 	return ret;
 }
 EXPORT_SYMBOL_GPL(trace_remote_alloc_buffer);
+
+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:%zu;\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_format_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 *key, const void *data)
+{
+	const struct remote_event *evt = data;
+	int id = (int)((long)key);
+
+	return id - (int)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);
+}
-- 
2.51.0

[for-next][PATCH 10/18] tracing: Add events/ root files to trace remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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

Link: https://patch.msgid.link/20260309162516.2623589-11-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c  |   3 +-
 kernel/trace/trace_remote.c | 138 +++++++++++++++++++++++++++++++++++-
 2 files changed, 139 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index fb39dd43e00b..605142e06863 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -640,7 +640,8 @@ 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 0d0af53c0ce9..0d78e5f5fe98 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -1125,10 +1125,145 @@ 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;
+	int i, ret;
+	u8 enable;
+
+	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 ssize_t remote_events_dir_enable_read(struct file *filp, char __user *ubuf, size_t cnt,
+					     loff_t *ppos)
+{
+	struct trace_remote *remote = file_inode(filp)->i_private;
+	const char enabled_char[] = {'0', '1', 'X'};
+	char enabled_str[] = " \n";
+	int i, enabled = -1;
+
+	guard(mutex)(&remote->lock);
+
+	for (i = 0; i < remote->nr_events; i++) {
+		struct remote_event *evt = &remote->events[i];
+
+		if (enabled == -1) {
+			enabled = evt->enabled;
+		} else if (enabled != evt->enabled) {
+			enabled = 2;
+			break;
+		}
+	}
+
+	enabled_str[0] = enabled_char[enabled == -1 ? 0 : enabled];
+
+	return simple_read_from_buffer(ubuf, cnt, ppos, enabled_str, 2);
+}
+
+static const struct file_operations remote_events_dir_enable_fops = {
+	.write = remote_events_dir_enable_write,
+	.read = remote_events_dir_enable_read,
+};
+
+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 = TRACEFS_MODE_WRITE;
+		*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",
@@ -1144,7 +1279,8 @@ 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);
 
-- 
2.51.0

[for-next][PATCH 11/18] tracing: Add helpers to create trace remote events

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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)
 )

Link: https://patch.msgid.link/20260309162516.2623589-12-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/trace_remote_event.h   | 10 ++++
 include/trace/define_remote_events.h | 73 ++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 include/trace/define_remote_events.h

diff --git a/include/linux/trace_remote_event.h b/include/linux/trace_remote_event.h
index a4449008a075..c8ae1e1f5e72 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..676e803dc144
--- /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(__args...) \
+	__COUNT_ARGS(, ##__args, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 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)
-- 
2.51.0

[for-next][PATCH 12/18] ring-buffer: Export buffer_data_page and macros

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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

Link: https://patch.msgid.link/20260309162516.2623589-13-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/ring_buffer_types.h | 41 +++++++++++++++++++++++++++++++
 kernel/trace/ring_buffer.c        | 36 +--------------------------
 2 files changed, 42 insertions(+), 35 deletions(-)
 create mode 100644 include/linux/ring_buffer_types.h

diff --git a/include/linux/ring_buffer_types.h b/include/linux/ring_buffer_types.h
new file mode 100644
index 000000000000..54577021a49d
--- /dev/null
+++ b/include/linux/ring_buffer_types.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_RING_BUFFER_TYPES_H
+#define _LINUX_RING_BUFFER_TYPES_H
+
+#include <asm/local.h>
+
+#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);
+}
+
+#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 */
+};
+#endif
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 605142e06863..96e0d80d492b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4,6 +4,7 @@
  *
  * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
  */
+#include <linux/ring_buffer_types.h>
 #include <linux/sched/isolation.h>
 #include <linux/trace_recursion.h>
 #include <linux/trace_events.h>
@@ -157,23 +158,6 @@ 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
 
@@ -316,10 +300,6 @@ 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;
@@ -338,12 +318,6 @@ 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 */
@@ -437,14 +411,6 @@ static struct buffer_data_page *alloc_cpu_data(int cpu, int order)
 	return dpage;
 }
 
-/*
- * 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;
-- 
2.51.0

[for-next][PATCH 13/18] tracing: Introduce simple_ring_buffer

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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.

Link: https://patch.msgid.link/20260309162516.2623589-14-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/simple_ring_buffer.h |  57 ++++
 kernel/trace/Kconfig               |   3 +
 kernel/trace/Makefile              |   1 +
 kernel/trace/simple_ring_buffer.c  | 464 +++++++++++++++++++++++++++++
 4 files changed, 525 insertions(+)
 create mode 100644 include/linux/simple_ring_buffer.h
 create mode 100644 kernel/trace/simple_ring_buffer.c

diff --git a/include/linux/simple_ring_buffer.h b/include/linux/simple_ring_buffer.h
new file mode 100644
index 000000000000..2c4c0ae336bc
--- /dev/null
+++ b/include/linux/simple_ring_buffer.h
@@ -0,0 +1,57 @@
+/* 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/ring_buffer_types.h>
+#include <linux/types.h>
+
+/*
+ * Ideally those struct would stay private but the caller needs to know
+ * the allocation size for simple_ring_buffer_init().
+ */
+struct simple_buffer_page {
+	struct list_head	link;
+	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;
+};
+
+int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_buffer_page *bpages,
+			    const struct ring_buffer_desc *desc);
+
+void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer);
+
+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);
+
+int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool enable);
+
+int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer);
+
+int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer);
+
+#endif
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 384dd36c8e29..edbdd7b38f61 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -1284,4 +1284,7 @@ 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 318923ce39f5..2e39b09398b3 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -129,4 +129,5 @@ 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..15df9781411b
--- /dev/null
+++ b/kernel/trace/simple_ring_buffer.c
@@ -0,0 +1,464 @@
+// 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>
+
+enum simple_rb_link_type {
+	SIMPLE_RB_LINK_NORMAL		= 0,
+	SIMPLE_RB_LINK_HEAD		= 1,
+	SIMPLE_RB_LINK_HEAD_MOVING
+};
+
+#define SIMPLE_RB_LINK_MASK ~(SIMPLE_RB_LINK_HEAD | SIMPLE_RB_LINK_HEAD_MOVING)
+
+static void simple_bpage_set_head_link(struct simple_buffer_page *bpage)
+{
+	unsigned long link = (unsigned long)bpage->link.next;
+
+	link &= SIMPLE_RB_LINK_MASK;
+	link |= SIMPLE_RB_LINK_HEAD;
+
+	/*
+	 * Paired with simple_rb_find_head() to order access between the head
+	 * link and overrun. It ensures we always report an up-to-date value
+	 * after swapping the reader page.
+	 */
+	smp_store_release(&bpage->link.next, (struct list_head *)link);
+}
+
+static bool simple_bpage_unset_head_link(struct simple_buffer_page *bpage,
+					 struct simple_buffer_page *dst,
+					 enum simple_rb_link_type new_type)
+{
+	unsigned long *link = (unsigned long *)(&bpage->link.next);
+	unsigned long old = (*link & SIMPLE_RB_LINK_MASK) | SIMPLE_RB_LINK_HEAD;
+	unsigned long new = (unsigned long)(&dst->link) | new_type;
+
+	return try_cmpxchg(link, &old, new);
+}
+
+static void simple_bpage_set_normal_link(struct simple_buffer_page *bpage)
+{
+	unsigned long link = (unsigned long)bpage->link.next;
+
+	WRITE_ONCE(bpage->link.next, (struct list_head *)(link & SIMPLE_RB_LINK_MASK));
+}
+
+static struct simple_buffer_page *simple_bpage_from_link(struct list_head *link)
+{
+	unsigned long ptr = (unsigned long)link & SIMPLE_RB_LINK_MASK;
+
+	return container_of((struct list_head *)ptr, struct simple_buffer_page, link);
+}
+
+static struct simple_buffer_page *simple_bpage_next_page(struct simple_buffer_page *bpage)
+{
+	return simple_bpage_from_link(bpage->link.next);
+}
+
+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->link);
+	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;
+}
+
+static int simple_rb_find_head(struct simple_rb_per_cpu *cpu_buffer)
+{
+	int retry = cpu_buffer->nr_pages * 2;
+	struct simple_buffer_page *head;
+
+	head = cpu_buffer->head_page;
+
+	while (retry--) {
+		unsigned long link;
+
+spin:
+		/* See smp_store_release in simple_bpage_set_head_link() */
+		link = (unsigned long)smp_load_acquire(&head->link.prev->next);
+
+		switch (link & ~SIMPLE_RB_LINK_MASK) {
+		/* Found the head */
+		case SIMPLE_RB_LINK_HEAD:
+			cpu_buffer->head_page = head;
+			return 0;
+		/* The writer caught the head, we can spin, that won't be long */
+		case SIMPLE_RB_LINK_HEAD_MOVING:
+			goto spin;
+		}
+
+		head = simple_bpage_next_page(head);
+	}
+
+	return -EBUSY;
+}
+
+/**
+ * simple_ring_buffer_swap_reader_page - Swap ring-buffer head with the reader
+ * @cpu_buffer: A simple_rb_per_cpu
+ *
+ * This function enables consuming reading. It ensures the current head page will not be overwritten
+ * and can be safely read.
+ *
+ * Returns 0 on success, -ENODEV if @cpu_buffer was unloaded or -EBUSY if we failed to catch the
+ * head page.
+ */
+int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer)
+{
+	struct simple_buffer_page *last, *head, *reader;
+	unsigned long overrun;
+	int retry = 8;
+	int ret;
+
+	if (!simple_rb_loaded(cpu_buffer))
+		return -ENODEV;
+
+	reader = cpu_buffer->reader_page;
+
+	do {
+		/* Run after the writer to find the head */
+		ret = simple_rb_find_head(cpu_buffer);
+		if (ret)
+			return ret;
+
+		head = cpu_buffer->head_page;
+
+		/* Connect the reader page around the header page */
+		reader->link.next = head->link.next;
+		reader->link.prev = head->link.prev;
+
+		/* The last page before the head */
+		last = simple_bpage_from_link(head->link.prev);
+
+		/* The reader page points to the new header page */
+		simple_bpage_set_head_link(reader);
+
+		overrun = cpu_buffer->meta->overrun;
+	} while (!simple_bpage_unset_head_link(last, reader, SIMPLE_RB_LINK_NORMAL) && retry--);
+
+	if (!retry)
+		return -EINVAL;
+
+	cpu_buffer->head_page = simple_bpage_from_link(reader->link.next);
+	cpu_buffer->head_page->link.prev = &reader->link;
+	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;
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_swap_reader_page);
+
+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_unset_head_link(tail, new_tail, SIMPLE_RB_LINK_HEAD_MOVING)) {
+		/*
+		 * 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(cpu_buffer->meta->pages_lost, 1);
+
+		simple_bpage_set_head_link(new_tail);
+		simple_bpage_set_normal_link(tail);
+	}
+
+	simple_bpage_reset(new_tail);
+	cpu_buffer->tail_page = new_tail;
+
+	simple_rb_meta_inc(cpu_buffer->meta->pages_touched, 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;
+}
+
+/**
+ * simple_ring_buffer_reserve - Reserve an entry in @cpu_buffer
+ * @cpu_buffer:	A simple_rb_per_cpu
+ * @length:	Size of the entry in bytes
+ * @timestamp:	Timestamp of the entry
+ *
+ * Returns the address of the entry where to write data or NULL
+ */
+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];
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_reserve);
+
+/**
+ * simple_ring_buffer_commit - Commit the entry reserved with simple_ring_buffer_reserve()
+ * @cpu_buffer:	The simple_rb_per_cpu where the entry has been reserved
+ */
+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);
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_commit);
+
+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;
+}
+
+/**
+ * simple_ring_buffer_reset - Reset @cpu_buffer
+ * @cpu_buffer: A simple_rb_per_cpu
+ *
+ * This will not clear the content of the data, only reset counters and pointers
+ *
+ * Returns 0 on success or -ENODEV if @cpu_buffer was unloaded.
+ */
+int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer)
+{
+	struct simple_buffer_page *bpage;
+	u32 prev_status;
+	int ret;
+
+	if (!simple_rb_loaded(cpu_buffer))
+		return -ENODEV;
+
+	prev_status = simple_rb_enable_tracing(cpu_buffer, false);
+
+	ret = simple_rb_find_head(cpu_buffer);
+	if (ret)
+		return ret;
+
+	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;
+	cpu_buffer->meta->pages_lost = 0;
+	cpu_buffer->meta->pages_touched = 0;
+
+	if (prev_status == SIMPLE_RB_READY)
+		simple_rb_enable_tracing(cpu_buffer, true);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_reset);
+
+/**
+ * simple_ring_buffer_init - Init @cpu_buffer based on @desc
+ * @cpu_buffer:	A simple_rb_per_cpu buffer to init, allocated by the caller.
+ * @bpages:	Array of simple_buffer_pages, with as many elements as @desc->nr_page_va
+ * @desc:	A ring_buffer_desc
+ *
+ * Returns 0 on success or -EINVAL if the content of @desc is invalid
+ */
+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 two pages in the ring-buffer */
+	if (desc->nr_page_va < 3)
+		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->link.next = &(bpage + 1)->link;
+		bpage->link.prev = &(bpage - 1)->link;
+		bpage->id = i;
+
+		cpu_buffer->nr_pages = i + 1;
+	}
+
+	/* Close the ring */
+	bpage->link.next = &cpu_buffer->tail_page->link;
+	cpu_buffer->tail_page->link.prev = &bpage->link;
+
+	/* The last init'ed page points to the head page */
+	simple_bpage_set_head_link(bpage);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_init);
+
+/**
+ * simple_ring_buffer_unload - Prepare @cpu_buffer for deletion
+ * @cpu_buffer:	A simple_rb_per_cpu that will be deleted.
+ */
+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 = NULL;
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_unload);
+
+/**
+ * simple_ring_buffer_enable_tracing - Enable or disable writing to @cpu_buffer
+ * @cpu_buffer: A simple_rb_per_cpu
+ * @enable:	True to enable tracing, False to disable it
+ *
+ * Returns 0 on success or -ENODEV if @cpu_buffer was unloaded
+ */
+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;
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_enable_tracing);
-- 
2.51.0

[for-next][PATCH 14/18] tracing: Add a trace remote module for testing

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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.

Link: https://patch.msgid.link/20260309162516.2623589-15-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 fs/tracefs/inode.c                |   1 +
 kernel/trace/Kconfig              |   8 +
 kernel/trace/Makefile             |   2 +
 kernel/trace/remote_test.c        | 261 ++++++++++++++++++++++++++++++
 kernel/trace/remote_test_events.h |  10 ++
 5 files changed, 282 insertions(+)
 create mode 100644 kernel/trace/remote_test.c
 create mode 100644 kernel/trace/remote_test_events.h

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 51c00c8fa175..edfdf139cb02 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -664,6 +664,7 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
 	fsnotify_create(d_inode(dentry->d_parent), dentry);
 	return tracefs_end_creating(dentry);
 }
+EXPORT_SYMBOL_GPL(tracefs_create_file);
 
 static struct dentry *__create_dir(const char *name, struct dentry *parent,
 				   const struct inode_operations *ops)
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index edbdd7b38f61..e130da35808f 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -1287,4 +1287,12 @@ 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 2e39b09398b3..d106beca8d7f 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -130,4 +130,6 @@ 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..6c1b7701ddae
--- /dev/null
+++ b/kernel/trace/remote_test.c
@@ -0,0 +1,261 @@
+// 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 = kmalloc_obj(*cpu_buffer);
+	if (!cpu_buffer)
+		return ret;
+
+	bpages = kmalloc_objs(*bpages, rb_desc->nr_page_va);
+	if (!bpages)
+		goto err_free_cpu_buffer;
+
+	ret = simple_ring_buffer_init(cpu_buffer, bpages, rb_desc);
+	if (ret)
+		goto err_free_bpages;
+
+	scoped_guard(mutex, &simple_rbs_lock) {
+		WARN_ON(*per_cpu_ptr(&simple_rbs, cpu));
+		*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 ERR_PTR(-EINVAL);
+
+	desc_size = trace_buffer_desc_size(size, num_possible_cpus());
+	if (desc_size == SIZE_MAX) {
+		ret = -E2BIG;
+		goto err;
+	}
+
+	desc = kmalloc(desc_size, GFP_KERNEL);
+	if (!desc) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	ret = trace_remote_alloc_buffer(desc, desc_size, size, cpu_possible_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_unload;
+	}
+
+	remote_test_buffer_desc = desc;
+
+	return remote_test_buffer_desc;
+
+err_unload:
+	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:
+	return ERR_PTR(ret);
+}
+
+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);
+	kfree(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 -ENODEV;
+
+	guard(preempt)();
+
+	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..26b93b3406fc
--- /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=%llu", __entry->id)
+);
-- 
2.51.0

[for-next][PATCH 15/18] tracing: selftests: Add trace remote tests

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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)
  * consuming read (trace_pipe.tc)
  * non-consuming read (trace.tc)

Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: linux-kselftest@vger.kernel.org
Link: https://patch.msgid.link/20260309162516.2623589-16-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 .../ftrace/test.d/remotes/buffer_size.tc      |  25 ++++
 .../selftests/ftrace/test.d/remotes/functions |  88 ++++++++++++
 .../selftests/ftrace/test.d/remotes/reset.tc  |  90 +++++++++++++
 .../selftests/ftrace/test.d/remotes/trace.tc  | 127 ++++++++++++++++++
 .../ftrace/test.d/remotes/trace_pipe.tc       | 127 ++++++++++++++++++
 .../ftrace/test.d/remotes/unloading.tc        |  41 ++++++
 6 files changed, 498 insertions(+)
 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/reset.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/trace.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

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..1a43280ffa97
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/buffer_size.tc
@@ -0,0 +1,25 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote buffer size
+# requires: remotes/test
+
+. $TEST_DIR/remotes/functions
+
+test_buffer_size()
+{
+    echo 0 > tracing_on
+    assert_unloaded
+
+    echo 4096 > buffer_size_kb
+    echo 1 > tracing_on
+    assert_loaded
+
+    echo 0 > tracing_on
+    echo 7 > buffer_size_kb
+}
+
+if [ -z "$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..97a09d564a34
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/functions
@@ -0,0 +1,88 @@
+# 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 $TRACING_DIR/remotes/test/ ] || modprobe remote_test || exit_unresolved
+
+	setup_remote "test"
+}
+
+assert_loaded()
+{
+	grep -q "(loaded)" buffer_size_kb
+}
+
+assert_unloaded()
+{
+	grep -q "(unloaded)" buffer_size_kb
+}
+
+dump_trace_pipe()
+{
+    output=$(mktemp $TMPDIR/remote_test.XXXXXX)
+    cat trace_pipe > $output &
+    pid=$!
+    sleep 1
+    kill -1 $pid
+
+    echo $output
+}
+
+check_trace()
+{
+	start_id="$1"
+	end_id="$2"
+	file="$3"
+
+	# Ensure the file is not empty
+	test -n "$(head $file)"
+
+	prev_ts=0
+	id=0
+
+	# Only keep <timestamp> <id>
+	tmp=$(mktemp $TMPDIR/remote_test.XXXXXX)
+	sed -e 's/\[[0-9]*\]\s*\([0-9]*.[0-9]*\): [a-z]* id=\([0-9]*\)/\1 \2/' $file > $tmp
+
+	while IFS= read -r line; do
+		ts=$(echo $line | cut -d ' ' -f 1)
+		id=$(echo $line | cut -d ' ' -f 2)
+
+		test $(echo "$ts>$prev_ts" | bc) -eq 1
+		test $id -eq $start_id
+
+		prev_ts=$ts
+		start_id=$((start_id + 1))
+	done < $tmp
+
+	test $id -eq $end_id
+	rm $tmp
+}
+
+get_cpu_ids()
+{
+    sed -n 's/^processor\s*:\s*\([0-9]\+\).*/\1/p' /proc/cpuinfo
+}
+
+get_page_size() {
+    sed -ne 's/^.*data.*size:\([0-9][0-9]*\).*/\1/p' events/header_page
+}
+
+get_selftest_event_size() {
+    sed -ne 's/^.*field:.*;.*size:\([0-9][0-9]*\);.*/\1/p' events/*/selftest/format | awk '{s+=$1} END {print s}'
+}
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..4d176349b2bc
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/reset.tc
@@ -0,0 +1,90 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote reset
+# requires: remotes/test
+
+. $TEST_DIR/remotes/functions
+
+check_reset()
+{
+    write_event_path="write_event"
+    taskset=""
+
+    clear_trace
+
+    # Is the buffer empty?
+    output=$(dump_trace_pipe)
+    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_pipe)
+    test $(wc -l $output | cut -d ' ' -f1) -eq 1
+    grep -q "id=7890" $output
+    rm $output
+}
+
+test_global_interface()
+{
+    output=$(mktemp $TMPDIR/remote_test.XXXXXX)
+
+    # Confidence check
+    echo 123456 > write_event
+    output=$(dump_trace_pipe)
+    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_pipe)
+            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.tc b/tools/testing/selftests/ftrace/test.d/remotes/trace.tc
new file mode 100644
index 000000000000..170f7648732a
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/trace.tc
@@ -0,0 +1,127 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote non-consuming read
+# requires: remotes/test
+
+. $TEST_DIR/remotes/functions
+
+test_trace()
+{
+	echo 0 > tracing_on
+    assert_unloaded
+
+    echo 7 > buffer_size_kb
+    echo 1 > tracing_on
+    assert_loaded
+
+    # Simple test: Emit few events and try to read them
+    for i in $(seq 1 8); do
+        echo $i > write_event
+    done
+
+    check_trace 1 8 trace
+
+    #
+    # Test interaction with consuming read
+    #
+
+    cat trace_pipe > /dev/null &
+    pid=$!
+
+    sleep 1
+    kill $pid
+
+    test $(wc -l < trace) -eq 0
+
+    for i in $(seq 16 32); do
+        echo $i > write_event
+    done
+
+    check_trace 16 32 trace
+
+    #
+    # Test interaction with reset
+    #
+
+    echo 0 > trace
+
+    test $(wc -l < trace) -eq 0
+
+    for i in $(seq 1 8); do
+        echo $i > write_event
+    done
+
+    check_trace 1 8 trace
+
+    #
+    # Test interaction with lost events
+    #
+
+    # Ensure the writer is not on the reader page by reloading the buffer
+    echo 0 > tracing_on
+    echo 0 > trace
+    assert_unloaded
+    echo 1 > tracing_on
+    assert_loaded
+
+    # Ensure ring-buffer overflow by emitting events from the same CPU
+    for cpu in $(get_cpu_ids); do
+        break
+    done
+
+    events_per_page=$(($(get_page_size) / $(get_selftest_event_size))) # Approx: does not take TS into account
+    nr_events=$(($events_per_page * 2))
+    for i in $(seq 1 $nr_events); do
+        taskset -c $cpu echo $i > write_event
+    done
+
+    id=$(sed -n -e '1s/\[[0-9]*\]\s*[0-9]*.[0-9]*: [a-z]* id=\([0-9]*\)/\1/p' trace)
+    test $id -ne 1
+
+    check_trace $id $nr_events trace
+
+    #
+    # Test per-CPU interface
+    #
+    echo 0 > trace
+
+    for cpu in $(get_cpu_ids) ; do
+        taskset -c $cpu echo $cpu > write_event
+    done
+
+    for cpu in $(get_cpu_ids); do
+        cd per_cpu/cpu$cpu/
+
+        check_trace $cpu $cpu trace
+
+        cd - > /dev/null
+    done
+
+    #
+    # Test with hotplug
+    #
+
+    [ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 0
+
+    echo 0 > trace
+
+    for cpu in $(get_cpu_ids); do
+        echo 0 > /sys/devices/system/cpu/cpu$cpu/online || return 0
+        break
+    done
+
+    for i in $(seq 1 8); do
+        echo $i > write_event
+    done
+
+    check_trace 1 8 trace
+
+    echo 1 > /sys/devices/system/cpu/cpu$cpu/online
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+    set -e
+
+    setup_remote_test
+    test_trace
+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..669a7288ed7c
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc
@@ -0,0 +1,127 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote consuming read
+# requires: remotes/test
+
+. $TEST_DIR/remotes/functions
+
+test_trace_pipe()
+{
+    echo 0 > tracing_on
+    assert_unloaded
+
+    # Emit events from the same CPU
+    for cpu in $(get_cpu_ids); do
+        break
+    done
+
+    #
+    # Simple test: Emit enough events to fill few pages
+    #
+
+    echo 1024 > buffer_size_kb
+    echo 1 > tracing_on
+    assert_loaded
+
+    events_per_page=$(($(get_page_size) / $(get_selftest_event_size)))
+    nr_events=$(($events_per_page * 4))
+
+    output=$(mktemp $TMPDIR/remote_test.XXXXXX)
+
+    cat trace_pipe > $output &
+    pid=$!
+
+    for i in $(seq 1 $nr_events); do
+        taskset -c $cpu echo $i > write_event
+    done
+
+    echo 0 > tracing_on
+    sleep 1
+    kill $pid
+
+    check_trace 1 $nr_events $output
+
+    rm $output
+
+    #
+    # Test interaction with lost events
+    #
+
+    assert_unloaded
+    echo 7 > buffer_size_kb
+    echo 1 > tracing_on
+    assert_loaded
+
+    nr_events=$((events_per_page * 2))
+    for i in $(seq 1 $nr_events); do
+        taskset -c $cpu echo $i > write_event
+    done
+
+    output=$(dump_trace_pipe)
+
+    lost_events=$(sed -n -e '1s/CPU:.*\[LOST \([0-9]*\) EVENTS\]/\1/p' $output)
+    test -n "$lost_events"
+
+    id=$(sed -n -e '2s/\[[0-9]*\]\s*[0-9]*.[0-9]*: [a-z]* id=\([0-9]*\)/\1/p' $output)
+    test "$id" -eq $(($lost_events + 1))
+
+    # Drop [LOST EVENTS] line
+    sed -i '1d' $output
+
+    check_trace $id $nr_events $output
+
+    rm $output
+
+    #
+    # Test per-CPU interface
+    #
+
+    echo 0 > trace
+    echo 1 > tracing_on
+
+    for cpu in $(get_cpu_ids); do
+        taskset -c $cpu echo $cpu > write_event
+    done
+
+    for cpu in $(get_cpu_ids); do
+        cd per_cpu/cpu$cpu/
+        output=$(dump_trace_pipe)
+
+        check_trace $cpu $cpu $output
+
+        rm $output
+        cd - > /dev/null
+    done
+
+    #
+    # Test interaction with hotplug
+    #
+
+    [ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 0
+
+    echo 0 > trace
+
+    for cpu in $(get_cpu_ids); do
+        echo 0 > /sys/devices/system/cpu/cpu$cpu/online || return 0
+        break
+    done
+
+    for i in $(seq 1 8); do
+        echo $i > write_event
+    done
+
+    output=$(dump_trace_pipe)
+
+    check_trace 1 8 $output
+
+    rm $output
+
+    echo 1 > /sys/devices/system/cpu/cpu$cpu/online
+}
+
+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..cac2190183f6
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/remotes/unloading.tc
@@ -0,0 +1,41 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote unloading
+# requires: remotes/test
+
+. $TEST_DIR/remotes/functions
+
+test_unloading()
+{
+    # No reader, writing
+    assert_loaded
+
+    # No reader, no writing
+    echo 0 > tracing_on
+    assert_unloaded
+
+    # 1 reader, no writing
+    cat trace_pipe &
+    pid=$!
+    sleep 1
+    assert_loaded
+    kill $pid
+    assert_unloaded
+
+    # No reader, no writing, events
+    echo 1 > tracing_on
+    echo 1 > write_event
+    echo 0 > tracing_on
+    assert_loaded
+
+    # Test reset
+    clear_trace
+    assert_unloaded
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+    set -e
+
+    setup_remote_test
+    test_unloading
+fi
-- 
2.51.0

[for-next][PATCH 16/18] Documentation: tracing: Add tracing remotes

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

Add documentation about the newly introduced tracing remotes framework.

Link: https://patch.msgid.link/20260309162516.2623589-17-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 Documentation/trace/index.rst   | 11 ++++++
 Documentation/trace/remotes.rst | 66 +++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+)
 create mode 100644 Documentation/trace/remotes.rst

diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index 338bc4d7cfab..036db96864d2 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -91,6 +91,17 @@ interactions.
    user_events
    uprobetracer
 
+Remote Tracing
+--------------
+
+This section covers the framework to read compatible ring-buffers, written by
+entities outside of the kernel (most likely firmware or hypervisor)
+
+.. toctree::
+   :maxdepth: 1
+
+   remotes
+
 Additional Resources
 --------------------
 
diff --git a/Documentation/trace/remotes.rst b/Documentation/trace/remotes.rst
new file mode 100644
index 000000000000..1f9d764f69aa
--- /dev/null
+++ b/Documentation/trace/remotes.rst
@@ -0,0 +1,66 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Tracing Remotes
+===============
+
+:Author: Vincent Donnefort <vdonnefort@google.com>
+
+Overview
+========
+Firmware and hypervisors are black boxes to the kernel. Having a way to see what
+they are doing can be useful to debug both. This is where remote tracing buffers
+come in. A remote tracing buffer is a ring buffer executed by the firmware or
+hypervisor into memory that is memory mapped to the host kernel. This is similar
+to how user space memory maps the kernel ring buffer but in this case the kernel
+is acting like user space and the firmware or hypervisor is the "kernel" side.
+With a trace remote ring buffer, the firmware and hypervisor can record events
+for which the host kernel can see and expose to user space.
+
+Register a remote
+=================
+A remote must provide a set of callbacks `struct trace_remote_callbacks` whom
+description can be found below. Those callbacks allows Tracefs to enable and
+disable tracing and events, to load and unload a tracing buffer (a set of
+ring-buffers) and to swap a reader page with the head page, which enables
+consuming reading.
+
+.. kernel-doc:: include/linux/trace_remote.h
+
+Once registered, an instance will appear for this remote in the Tracefs
+directory **remotes/**. Buffers can then be read using the usual Tracefs files
+**trace_pipe** and **trace**.
+
+Declare a remote event
+======================
+Macros are provided to ease the declaration of remote events, in a similar
+fashion to in-kernel events. A declaration must provide an ID, a description of
+the event arguments and how to print the event:
+
+.. code-block:: c
+
+	REMOTE_EVENT(foo, EVENT_FOO_ID,
+		RE_STRUCT(
+			re_field(u64, bar)
+		),
+		RE_PRINTK("bar=%lld", __entry->bar)
+	);
+
+Then those events must be declared in a C file with the following:
+
+.. code-block:: c
+
+	#define REMOTE_EVENT_INCLUDE_FILE foo_events.h
+	#include <trace/define_remote_events.h>
+
+This will provide a `struct remote_event remote_event_foo` that can be given to
+`trace_remote_register`.
+
+Registered events appear in the remote directory under **events/**.
+
+Simple ring-buffer
+==================
+A simple implementation for a ring-buffer writer can be found in
+kernel/trace/simple_ring_buffer.c.
+
+.. kernel-doc:: include/linux/simple_ring_buffer.h
-- 
2.51.0

[for-next][PATCH 17/18] tracing: load/unload page callbacks for simple_ring_buffer

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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.

Link: https://patch.msgid.link/20260309162516.2623589-18-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/simple_ring_buffer.h |  8 +++
 kernel/trace/simple_ring_buffer.c  | 91 +++++++++++++++++++++++-------
 2 files changed, 80 insertions(+), 19 deletions(-)

diff --git a/include/linux/simple_ring_buffer.h b/include/linux/simple_ring_buffer.h
index 2c4c0ae336bc..21aec556293e 100644
--- a/include/linux/simple_ring_buffer.h
+++ b/include/linux/simple_ring_buffer.h
@@ -54,4 +54,12 @@ int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer);
 
 int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer);
 
+int simple_ring_buffer_init_mm(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_mm(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 15df9781411b..02af2297ae5a 100644
--- a/kernel/trace/simple_ring_buffer.c
+++ b/kernel/trace/simple_ring_buffer.c
@@ -71,7 +71,7 @@ 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->link);
 	bpage->page = (struct buffer_data_page *)page;
@@ -372,18 +372,15 @@ int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer)
 }
 EXPORT_SYMBOL_GPL(simple_ring_buffer_reset);
 
-/**
- * simple_ring_buffer_init - Init @cpu_buffer based on @desc
- * @cpu_buffer:	A simple_rb_per_cpu buffer to init, allocated by the caller.
- * @bpages:	Array of simple_buffer_pages, with as many elements as @desc->nr_page_va
- * @desc:	A ring_buffer_desc
- *
- * Returns 0 on success or -EINVAL if the content of @desc is invalid
- */
-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_mm(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 two pages in the ring-buffer */
@@ -392,15 +389,22 @@ 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;
@@ -410,7 +414,13 @@ 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->link.next = &(bpage + 1)->link;
 		bpage->link.prev = &(bpage - 1)->link;
@@ -419,6 +429,14 @@ 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->link.next = &cpu_buffer->tail_page->link;
 	cpu_buffer->tail_page->link.prev = &bpage->link;
@@ -426,23 +444,58 @@ 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_head_link(bpage);
 
+	cpu_buffer->bpages = bpages;
+
 	return 0;
 }
-EXPORT_SYMBOL_GPL(simple_ring_buffer_init);
+
+static void *__load_page(unsigned long page)
+{
+	return (void *)page;
+}
+
+static void __unload_page(void *page) { }
 
 /**
- * simple_ring_buffer_unload - Prepare @cpu_buffer for deletion
- * @cpu_buffer:	A simple_rb_per_cpu that will be deleted.
+ * simple_ring_buffer_init - Init @cpu_buffer based on @desc
+ * @cpu_buffer:	A simple_rb_per_cpu buffer to init, allocated by the caller.
+ * @bpages:	Array of simple_buffer_pages, with as many elements as @desc->nr_page_va
+ * @desc:	A ring_buffer_desc
+ *
+ * Returns 0 on success or -EINVAL if the content of @desc is invalid
  */
-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)
+{
+	return simple_ring_buffer_init_mm(cpu_buffer, bpages, desc, __load_page, __unload_page);
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_init);
+
+void simple_ring_buffer_unload_mm(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 = NULL;
 }
+
+/**
+ * simple_ring_buffer_unload - Prepare @cpu_buffer for deletion
+ * @cpu_buffer:	A simple_rb_per_cpu that will be deleted.
+ */
+void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer)
+{
+	return simple_ring_buffer_unload_mm(cpu_buffer, __unload_page);
+}
 EXPORT_SYMBOL_GPL(simple_ring_buffer_unload);
 
 /**
-- 
2.51.0

[for-next][PATCH 18/18] tracing: Check for undefined symbols in simple_ring_buffer

[Steven Rostedt]

From: Vincent Donnefort <vdonnefort@google.com>

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.

Link: https://patch.msgid.link/20260309162516.2623589-19-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/Makefile | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index d106beca8d7f..3182e1bc1cf7 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -132,4 +132,20 @@ 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 := memset alt_cb_patch_nops __x86 __ubsan __asan __kasan __gcov __aeabi_unwind
+UNDEFINED_ALLOWLIST += __stack_chk_fail stackleak_track_stack __ref_stack __sanitizer
+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
-- 
2.51.0