From: Steven Rostedt rostedt@goodmis.org
Some architectures do not have data cache coherency between user and kernel space. For these architectures, the cache needs to be flushed on both the kernel and user addresses so that user space can see the updates the kernel has made.
Instead of using flush_dcache_folio() and playing with virt_to_folio() within the call to that function, use flush_kernel_vmap_range() which takes the virtual address and does the work for those architectures that need it.
This also fixes a bug where the flush of the reader page only flushed one page. If the sub-buffer order is 1 or more, where the sub-buffer size would be greater than a page, it would miss the rest of the sub-buffer content, as the "reader page" is not just a page, but the size of a sub-buffer.
Link: https://lore.kernel.org/all/CAG48ez3w0my4Rwttbc5tEbNsme6tc0mrSN95thjXUFaJ3aQ...
Cc: stable@vger.kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Vincent Donnefort vdonnefort@google.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Mike Rapoport rppt@kernel.org Link: https://lore.kernel.org/20250402144953.920792197@goodmis.org Fixes: 117c39200d9d7 ("ring-buffer: Introducing ring-buffer mapping functions"); Suggested-by: Jann Horn jannh@google.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- kernel/trace/ring_buffer.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index f25966b3a1fc..d4b0f7b55cce 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6016,7 +6016,7 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) 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)); + flush_kernel_vmap_range(cpu_buffer->meta_page, PAGE_SIZE); }
static void @@ -7319,7 +7319,8 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
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)); + flush_kernel_vmap_range(cpu_buffer->reader_page->page, + buffer->subbuf_size + BUF_PAGE_HDR_SIZE);
rb_update_meta_page(cpu_buffer);