[PATCH 0/2] ring-buffer: Allow persistent memory to be user space mmapped

[PATCH 0/2] ring-buffer: Allow persistent memory to be user space mmapped

[Steven Rostedt]

Linus,

This is an update to the code that we discussed in making the persistent
ring buffer work with user space memory mapping. I based it on top of
the second version of the pull request I just sent out.

Note, I'm not suggesting this is to go into this merge window. I'm
happy to wait until the next window.

The first patch moves the memory mapping of the physical memory returned
by reserve_mem from the tracing code to the ring buffer code. This makes
sense as this gives more control over to the ring buffer in knowing exactly
how the pages were created. It keeps track of where the physical memory
that was mapped and also handles the freeing of this memory (removing the
burden from the tracing code from having to do this). It also handles
knowing if the buffer may be memory mapped or not. The check is removed
from the tracing code, but if the tracing code tries to memory map the
persistent ring buffer, the call to the ring buffer code will fail with
the same error as before.

The second patch implements the user space memory mapping of the persistent
ring buffer. It does so by adding several helper functions to annotate
what the code is doing. By doing this, I also discovered that that "hack" 
you did not like was not needed for the meta page. There's two meta pages
here. One is mapped between the kernel and user space and is used to inform
user space of updates to the ring buffer. The other is inside the persistent
memory that is used to pass information across boots. The persistent memory
meta data is never exposed to user space. The meta data for user space
mapping is always allocated via the normal memory allocation.

The helper functions are:

 rb_struct_page() - This is the rb_get_page() from our discussions, but
                    I renamed it because "get" implies "put".
                    This function will return the struct page for a given
                    buffer page by either virt_to_page() if the page was
                    allocated via the normal memory allocator, or it
                    is found via pfn_to_page() by using the saved physical
                    and virtual address of the mapped location. It uses
                    that to calculate the physical address from the virtual
                    address of the page and then pfn_to_page() can be used
                    from that.

  rb_fush_buffer_page() - this calls the above rb_struct_page() and then
                    calls flush_dcache_folio() to make sure the kernel
                    and user space is coherent.

  rb_flush_meta() - This just uses virt_to_page() and calls flush_dcache_folio()
                    as it is always allocated by the normal memory allocator.
                    I created it just to be consistent.

  rb_page_id() - The mappings require knowing where they are mapped.
                 As the normal allocated pages are done in a way that they
                 may exist anywhere from the kernel's point of view, they
                 need to be labelled to know where they are mapped in user
                 space. The bpage->id is used for this. But for the persistent
                 memory, that bpage->id is already used for knowing the order
                 of the pages that are still active in the write part of
                 the buffer. This means that they are not consecutive. For
                 the user space mapping, the index of where the pages exist
                 in the physical memory is used for the placement in user
                 space. In order to manage this difference between how the
                 ids are used, this helper function handles that.

I personally feel this version of the code is much cleaner and with the
helper functions, much easier to follow. As doing this exercise found that
the test against virt_addr_valid() wasn't needed in every location
(which is no longer used here).

Steven Rostedt (2):
      tracing: ring-buffer: Have the ring buffer code do the vmap of physical memory
      ring-buffer: Allow persistent ring buffers to be mmapped

----
 include/linux/ring_buffer.h |  19 ++---
 kernel/trace/ring_buffer.c  | 180 +++++++++++++++++++++++++++++++++++++++-----
 kernel/trace/trace.c        |  65 ++++------------
 3 files changed, 186 insertions(+), 78 deletions(-)

[PATCH 1/2] tracing: ring-buffer: Have the ring buffer code do the vmap of physical memory

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

Currently, when reserve_mem is used on the kernel command line to reserve
"persistent" memory to map the ring buffer on. The tracing code will do
the vmap() on the physical memory provided by reserve_mem and pass that to
ring_buffer_alloc_range() where it will map the ring buffer on top of the
given memory. It will also look at the current content of the memory there
and if the memory already contains valid content, it will use that content
for the ring buffer.

But this method makes the ring buffer code not know where that memory came
from. Here, the tracing code used vmap() but it could have also used
vmalloc(), or whatever. And many of these methods may not be supported by
the ring buffer code.

Instead, rename ring_buffer_alloc_range() to ring_buffer_alloc_physical()
where contiguous physical memory is passed to the ring buffer code, and it
will be responsible for mapping it as well as freeing it. This simplifies
the callers from having to keep track of whether the code is mapped or
not.

The ring buffer can also take control of whether it can memory map the
buffer to user space or not. Currently it does not allow this physical
memory to be mapped to user space, but now that it has control over the
struct pages of this memory, it can easily do so in the future.

As the ring buffer mapping of a physical memory mapped buffer will now
fail, the tracing code no longer keeps track if the buffer is the "last
boot" buffer or not and will try to map it anyway. It will still fail, but
when the ring buffer code is modified to allow it, it will then succeed.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/ring_buffer.h | 19 ++++----
 kernel/trace/ring_buffer.c  | 86 ++++++++++++++++++++++++++++++++-----
 kernel/trace/trace.c        | 65 +++++++---------------------
 3 files changed, 101 insertions(+), 69 deletions(-)

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 56e27263acf8..a31dff0a9f09 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -89,11 +89,11 @@ void ring_buffer_discard_commit(struct trace_buffer *buffer,
 struct trace_buffer *
 __ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *key);
 
-struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flags,
-					       int order, unsigned long start,
-					       unsigned long range_size,
-					       unsigned long scratch_size,
-					       struct lock_class_key *key);
+struct trace_buffer *__ring_buffer_alloc_physical(unsigned long size, unsigned flags,
+						  int order, unsigned long start,
+						  unsigned long range_size,
+						  unsigned long scratch_size,
+						  struct lock_class_key *key);
 
 void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size);
 
@@ -113,11 +113,11 @@ void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size);
  * traced by ftrace, it can produce lockdep warnings. We need to keep each
  * ring buffer's lock class separate.
  */
-#define ring_buffer_alloc_range(size, flags, order, start, range_size, s_size)	\
+#define ring_buffer_alloc_physical(size, flags, order, start, range_size, s_size) \
 ({									\
 	static struct lock_class_key __key;				\
-	__ring_buffer_alloc_range((size), (flags), (order), (start),	\
-				  (range_size), (s_size), &__key);	\
+	__ring_buffer_alloc_physical((size), (flags), (order), (start),	\
+				     (range_size), (s_size), &__key);	\
 })
 
 typedef bool (*ring_buffer_cond_fn)(void *data);
@@ -235,7 +235,8 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order);
 int ring_buffer_subbuf_size_get(struct trace_buffer *buffer);
 
 enum ring_buffer_flags {
-	RB_FL_OVERWRITE		= 1 << 0,
+	RB_FL_OVERWRITE		= BIT(0),
+	RB_FL_PHYSICAL		= BIT(1),
 };
 
 #ifdef CONFIG_RING_BUFFER
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f25966b3a1fc..0f5481d8d0b1 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -17,6 +17,7 @@
 #include <linux/uaccess.h>
 #include <linux/hardirq.h>
 #include <linux/kthread.h>	/* for self test */
+#include <linux/vmalloc.h>	/* for vmap */
 #include <linux/module.h>
 #include <linux/percpu.h>
 #include <linux/mutex.h>
@@ -556,6 +557,8 @@ struct trace_buffer {
 
 	struct ring_buffer_meta		*meta;
 
+	unsigned long			phys_start;
+
 	unsigned int			subbuf_size;
 	unsigned int			subbuf_order;
 	unsigned int			max_data_size;
@@ -2351,6 +2354,43 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 	kfree(cpu_buffer);
 }
 
+static unsigned long map_pages(unsigned long *start, unsigned long *end)
+{
+	struct page **pages;
+	phys_addr_t page_start;
+	unsigned long page_count;
+	unsigned long size;
+	unsigned long i;
+	void *vaddr;
+
+	/* Make sure the mappings are page aligned */
+	*start = ALIGN(*start, PAGE_SIZE);
+
+	size = *end - *start;
+
+	/* The size must fit full pages */
+	page_count = size >> PAGE_SHIFT;
+
+	if (!page_count)
+		return 0;
+
+	page_start = *start;
+	pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
+	if (!pages)
+		return 0;
+
+	for (i = 0; i < page_count; i++) {
+		phys_addr_t addr = page_start + i * PAGE_SIZE;
+		pages[i] = pfn_to_page(addr >> PAGE_SHIFT);
+	}
+	vaddr = vmap(pages, page_count, VM_MAP, PAGE_KERNEL);
+	kfree(pages);
+
+	*end = *start + page_count * PAGE_SIZE;
+
+	return (unsigned long)vaddr;
+}
+
 static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 					 int order, unsigned long start,
 					 unsigned long end,
@@ -2395,14 +2435,26 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 	if (!buffer->buffers)
 		goto fail_free_cpumask;
 
-	/* If start/end are specified, then that overrides size */
+	/* If start/end are specified, then this is a physical mapping */
 	if (start && end) {
 		unsigned long buffers_start;
+		unsigned long addr;
 		unsigned long ptr;
+		u64 size;
 		int n;
 
-		/* Make sure that start is word aligned */
-		start = ALIGN(start, sizeof(long));
+		addr = map_pages(&start, &end);
+		if (!addr)
+			goto fail_free_cpumask;
+
+		/* end and start have have been updated for alignment */
+		size = end - start;
+
+		buffer->phys_start = start;
+		buffer->flags |= RB_FL_PHYSICAL;
+
+		start = addr;
+		end = start + size;
 
 		/* scratch_size needs to be aligned too */
 		scratch_size = ALIGN(scratch_size, sizeof(long));
@@ -2479,6 +2531,9 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 	}
 	kfree(buffer->buffers);
 
+	if (buffer->phys_start)
+		vunmap((void *)buffer->phys_start);
+
  fail_free_cpumask:
 	free_cpumask_var(buffer->cpumask);
 
@@ -2508,11 +2563,11 @@ struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
 EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
 
 /**
- * __ring_buffer_alloc_range - allocate a new ring_buffer from existing memory
+ * __ring_buffer_alloc_physical - allocate a new ring_buffer from physical memory
  * @size: the size in bytes per cpu that is needed.
  * @flags: attributes to set for the ring buffer.
  * @order: sub-buffer order
- * @start: start of allocated range
+ * @start: start of the physical memory range
  * @range_size: size of allocated range
  * @scratch_size: size of scratch area (for preallocated memory buffers)
  * @key: ring buffer reader_lock_key.
@@ -2522,11 +2577,11 @@ EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
  * when the buffer wraps. If this flag is not set, the buffer will
  * drop data when the tail hits the head.
  */
-struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flags,
-					       int order, unsigned long start,
-					       unsigned long range_size,
-					       unsigned long scratch_size,
-					       struct lock_class_key *key)
+struct trace_buffer *__ring_buffer_alloc_physical(unsigned long size, unsigned flags,
+						  int order, unsigned long start,
+						  unsigned long range_size,
+						  unsigned long scratch_size,
+						  struct lock_class_key *key)
 {
 	return alloc_buffer(size, flags, order, start, start + range_size,
 			    scratch_size, key);
@@ -2569,6 +2624,9 @@ ring_buffer_free(struct trace_buffer *buffer)
 	kfree(buffer->buffers);
 	free_cpumask_var(buffer->cpumask);
 
+	if (buffer->flags & RB_FL_PHYSICAL)
+		vunmap((void *)buffer->phys_start);
+
 	kfree(buffer);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_free);
@@ -7138,6 +7196,14 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 	unsigned long flags, *subbuf_ids;
 	int err = 0;
 
+	/*
+	 * Currently, this does not support vmap()'d buffers.
+	 * Return -ENODEV as that is what is returned when a file
+	 * does not support memory mapping.
+	 */
+	if (buffer->flags & RB_FL_PHYSICAL)
+		return -ENODEV;
+
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return -EINVAL;
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 14c38fcd6f9e..20724d64e02e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8492,10 +8492,6 @@ static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma)
 	struct trace_iterator *iter = &info->iter;
 	int ret = 0;
 
-	/* Currently the boot mapped buffer is not supported for mmap */
-	if (iter->tr->flags & TRACE_ARRAY_FL_BOOT)
-		return -ENODEV;
-
 	ret = get_snapshot_map(iter->tr);
 	if (ret)
 		return ret;
@@ -8503,8 +8499,8 @@ static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma)
 	ret = ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file, vma);
 	if (ret)
 		put_snapshot_map(iter->tr);
-
-	vma->vm_ops = &tracing_buffers_vmops;
+	else
+		vma->vm_ops = &tracing_buffers_vmops;
 
 	return ret;
 }
@@ -9520,10 +9516,17 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size
 
 	if (tr->range_addr_start && tr->range_addr_size) {
 		/* Add scratch buffer to handle 128 modules */
-		buf->buffer = ring_buffer_alloc_range(size, rb_flags, 0,
-						      tr->range_addr_start,
-						      tr->range_addr_size,
-						      struct_size(tscratch, entries, 128));
+		buf->buffer = ring_buffer_alloc_physical(size, rb_flags, 0,
+							 tr->range_addr_start,
+							 tr->range_addr_size,
+							 struct_size(tscratch, entries, 128));
+		if (!buf->buffer) {
+			pr_warn("Tracing: Failed to map boot instance %s\n", tr->name);
+			return -1;
+		}
+
+		pr_info("Tracing: mapped boot instance %s at physical memory %lx of size 0x%lx\n",
+			tr->name, tr->range_addr_start, tr->range_addr_size);
 
 		tscratch = ring_buffer_meta_scratch(buf->buffer, &scratch_size);
 		setup_trace_scratch(tr, tscratch, scratch_size);
@@ -9600,9 +9603,6 @@ static void free_trace_buffers(struct trace_array *tr)
 #ifdef CONFIG_TRACER_MAX_TRACE
 	free_trace_buffer(&tr->max_buffer);
 #endif
-
-	if (tr->range_addr_start)
-		vunmap((void *)tr->range_addr_start);
 }
 
 static void init_trace_flags_index(struct trace_array *tr)
@@ -9795,31 +9795,6 @@ static int instance_mkdir(const char *name)
 	return ret;
 }
 
-static u64 map_pages(u64 start, u64 size)
-{
-	struct page **pages;
-	phys_addr_t page_start;
-	unsigned int page_count;
-	unsigned int i;
-	void *vaddr;
-
-	page_count = DIV_ROUND_UP(size, PAGE_SIZE);
-
-	page_start = start;
-	pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
-	if (!pages)
-		return 0;
-
-	for (i = 0; i < page_count; i++) {
-		phys_addr_t addr = page_start + i * PAGE_SIZE;
-		pages[i] = pfn_to_page(addr >> PAGE_SHIFT);
-	}
-	vaddr = vmap(pages, page_count, VM_MAP, PAGE_KERNEL);
-	kfree(pages);
-
-	return (u64)(unsigned long)vaddr;
-}
-
 /**
  * trace_array_get_by_name - Create/Lookup a trace array, given its name.
  * @name: The name of the trace array to be looked up/created.
@@ -10708,7 +10683,6 @@ __init static void enable_instances(void)
 	while ((curr_str = strsep(&str, "\t"))) {
 		phys_addr_t start = 0;
 		phys_addr_t size = 0;
-		unsigned long addr = 0;
 		bool traceprintk = false;
 		bool traceoff = false;
 		char *flag_delim;
@@ -10773,22 +10747,13 @@ __init static void enable_instances(void)
 			rname = kstrdup(tok, GFP_KERNEL);
 		}
 
-		if (start) {
-			addr = map_pages(start, size);
-			if (addr) {
-				pr_info("Tracing: mapped boot instance %s at physical memory %pa of size 0x%lx\n",
-					name, &start, (unsigned long)size);
-			} else {
-				pr_warn("Tracing: Failed to map boot instance %s\n", name);
-				continue;
-			}
-		} else {
+		if (!start) {
 			/* Only non mapped buffers have snapshot buffers */
 			if (IS_ENABLED(CONFIG_TRACER_MAX_TRACE))
 				do_allocate_snapshot(name);
 		}
 
-		tr = trace_array_create_systems(name, NULL, addr, size);
+		tr = trace_array_create_systems(name, NULL, (unsigned long)start, size);
 		if (IS_ERR(tr)) {
 			pr_warn("Tracing: Failed to create instance buffer %s\n", curr_str);
 			continue;
-- 
2.47.2

[PATCH 2/2] ring-buffer: Allow persistent ring buffers to be mmapped

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

The persistent ring buffer uses vmap()'d memory to map the reserved memory
from boot. But the user space mmap() to the ring buffer requires
virt_to_page() to return a valid page. But that only works for core kernel
addresses and not for vmap() addresses.

To address this, save the physical and virtual address of where the
persistent memory is mapped. Create a rb_struct_page() helper function
that returns the page via virt_to_page() for normal buffer pages that were
allocated with page_alloc() but for the physical memory vmap()'d pages, it
uses the saved physical and virtual addresses of where the memory was
located to calculate the physical address of the virtual page that needs
the struct page. Then it uses pfn_to_page() to get the page for that
physical address.

New helper functions are created for flushing the cache for architectures
that need it between user and kernel space.

Also, the persistent memory uses the page->id for its own purpose where as
the user mmap buffer currently uses that for the subbuf array mapped to
user space. If the buffer is a persistent buffer, use the page index into
that buffer as the identifier instead of the page->id.

That is, the page->id for a persistent buffer, represents the order of the
buffer is in the link list. ->id == 0 means it is the reader page.
When a reader page is swapped, the new reader page's ->id gets zero, and
the old reader page gets the ->id of the page that it swapped with.

The user space mapping has the ->id is the index of where it was mapped in
user space and does not change while it is mapped.

Since the persistent buffer is fixed in its location, the index of where
a page is in the memory range can be used as the "id" to put in the meta
page array, and it can be mapped in the same order to user space as it is
in the persistent memory.

A new rb_page_id() helper function is used to get and set the id depending
on if the page is a normal memory allocated buffer or a physical memory
mapped buffer.

Link: https://lore.kernel.org/all/CAHk-=wgD9MQOoMAGtT=fXZsWY39exRVyZgxuBXix4u=1bdHA=g@mail.gmail.com/

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 110 +++++++++++++++++++++++++++++++------
 1 file changed, 93 insertions(+), 17 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 0f5481d8d0b1..d5c502bc2b27 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -558,6 +558,7 @@ struct trace_buffer {
 	struct ring_buffer_meta		*meta;
 
 	unsigned long			phys_start;
+	unsigned long			virt_start;
 
 	unsigned int			subbuf_size;
 	unsigned int			subbuf_order;
@@ -2455,6 +2456,7 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags,
 
 		start = addr;
 		end = start + size;
+		buffer->virt_start = start;
 
 		/* scratch_size needs to be aligned too */
 		scratch_size = ALIGN(scratch_size, sizeof(long));
@@ -6058,6 +6060,80 @@ static void rb_clear_buffer_page(struct buffer_page *page)
 	page->read = 0;
 }
 
+/*
+ * Get the struct page for the given buffer page.
+ *
+ * For normal ring buffer pages that are allocated via page_alloc()
+ * the struct page can simply be retrieved via virt_to_page().
+ *
+ * But if the buffer was created via a physical mapping and vmap()
+ * was used to get to the virtual addresses, use the stored virtual
+ * and physical of the start address to calculate the original
+ * physical address of the given page and use pfn_to_page() to return
+ * the struct page.
+ */
+static struct page *rb_struct_page(struct trace_buffer *buffer, void *vaddr)
+{
+	if (buffer->flags & RB_FL_PHYSICAL) {
+		unsigned long addr = (unsigned long)vaddr;
+
+		addr -= buffer->virt_start;
+		addr += buffer->phys_start;
+		return pfn_to_page(addr >> PAGE_SHIFT);
+	}
+	return virt_to_page(vaddr);
+}
+
+/* Some archs do not have data cache coherency between kernel and user-space */
+static void rb_flush_buffer_page(struct trace_buffer *buffer,
+				 struct buffer_page *bpage)
+{
+	struct page *page = rb_struct_page(buffer, bpage->page);
+
+	flush_dcache_folio(page_folio(page));
+}
+
+/* The user mapped meta page is always allocated via page_alloc() */
+static void rb_flush_meta(void *meta)
+{
+	struct page *page = virt_to_page(meta);
+
+	flush_dcache_folio(page_folio(page));
+}
+
+/*
+ * When the buffer is memory mapped to user space, each sub buffer
+ * has a unique id that is used by the meta data to tell the user
+ * where the current reader page is.
+ *
+ * For a normal allocated ring buffer, the id is saved in the buffer page
+ * id field, and updated via this function.
+ *
+ * But for a physical memory mapped buffer, the id is already assigned for
+ * memory ording in the physical memory layout and can not be used. Instead
+ * the index of where the page lies in the memory layout is used.
+ *
+ * For the normal pages, set the buffer page id with the passed in @id
+ * value and return that.
+ *
+ * For memory mapped pages, get the page index in the physical memory layout
+ * and return that as the id.
+ */
+static int rb_page_id(struct ring_buffer_per_cpu *cpu_buffer,
+		      struct buffer_page *bpage, int id)
+{
+	/*
+	 * For boot buffers, the id is the index,
+	 * otherwise, set the buffer page with this id
+	 */
+	if (cpu_buffer->ring_meta)
+		id = rb_meta_subbuf_idx(cpu_buffer->ring_meta, bpage->page);
+	else
+		bpage->id = id;
+
+	return id;
+}
+
 static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	struct trace_buffer_meta *meta = cpu_buffer->meta_page;
@@ -6066,15 +6142,16 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
 		return;
 
 	meta->reader.read = cpu_buffer->reader_page->read;
-	meta->reader.id = cpu_buffer->reader_page->id;
+	meta->reader.id = rb_page_id(cpu_buffer, cpu_buffer->reader_page,
+				     cpu_buffer->reader_page->id);
+
 	meta->reader.lost_events = cpu_buffer->lost_events;
 
 	meta->entries = local_read(&cpu_buffer->entries);
 	meta->overrun = local_read(&cpu_buffer->overrun);
 	meta->read = cpu_buffer->read;
 
-	/* Some archs do not have data cache coherency between kernel and user-space */
-	flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page));
+	rb_flush_meta(meta);
 }
 
 static void
@@ -6982,23 +7059,29 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
 	struct trace_buffer_meta *meta = cpu_buffer->meta_page;
 	unsigned int nr_subbufs = cpu_buffer->nr_pages + 1;
 	struct buffer_page *first_subbuf, *subbuf;
+	int cnt = 0;
 	int id = 0;
 
-	subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page;
-	cpu_buffer->reader_page->id = id++;
+	id = rb_page_id(cpu_buffer, cpu_buffer->reader_page, id);
+	subbuf_ids[id++] = (unsigned long)cpu_buffer->reader_page->page;
+	cnt++;
 
 	first_subbuf = subbuf = rb_set_head_page(cpu_buffer);
 	do {
+		id = rb_page_id(cpu_buffer, subbuf, id);
+
 		if (WARN_ON(id >= nr_subbufs))
 			break;
 
 		subbuf_ids[id] = (unsigned long)subbuf->page;
-		subbuf->id = id;
 
 		rb_inc_page(&subbuf);
 		id++;
+		cnt++;
 	} while (subbuf != first_subbuf);
 
+	WARN_ON(cnt != nr_subbufs);
+
 	/* install subbuf ID to kern VA translation */
 	cpu_buffer->subbuf_ids = subbuf_ids;
 
@@ -7134,6 +7217,7 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
 	if (!pgoff) {
 		unsigned long meta_page_padding;
 
+		/* The meta page is always allocated via alloc_page() */
 		pages[p++] = virt_to_page(cpu_buffer->meta_page);
 
 		/*
@@ -7163,7 +7247,8 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
 			goto out;
 		}
 
-		page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]);
+		page = rb_struct_page(cpu_buffer->buffer,
+				      (void *)cpu_buffer->subbuf_ids[s]);
 
 		for (; off < (1 << (subbuf_order)); off++, page++) {
 			if (p >= nr_pages)
@@ -7196,14 +7281,6 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 	unsigned long flags, *subbuf_ids;
 	int err = 0;
 
-	/*
-	 * Currently, this does not support vmap()'d buffers.
-	 * Return -ENODEV as that is what is returned when a file
-	 * does not support memory mapping.
-	 */
-	if (buffer->flags & RB_FL_PHYSICAL)
-		return -ENODEV;
-
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return -EINVAL;
 
@@ -7384,8 +7461,7 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
 	goto consume;
 
 out:
-	/* Some archs do not have data cache coherency between kernel and user-space */
-	flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page));
+	rb_flush_buffer_page(buffer, cpu_buffer->reader_page);
 
 	rb_update_meta_page(cpu_buffer);
 
-- 
2.47.2