[PATCH AUTOSEL 6.13 7/8] tracing: Enforce the persistent ring buffer to be page aligned

Sasha Levin
2025-04-07T18:17:16Z

From: Steven Rostedt <rostedt@goodmis.org>

[ Upstream commit c44a14f216f45d8bf1634b52854a699d7090f1e8 ]

Enforce that the address and the size of the memory used by the persistent
ring buffer is page aligned. Also update the documentation to reflect this
requirement.

Link: https://lore.kernel.org/all/CAHk-=whUOfVucfJRt7E0AH+GV41ELmS4wJqxHDnui6Giddfkzw@mail.gmail.com/

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>
Cc: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/20250402144953.412882844@goodmis.org
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 2 ++
Documentation/trace/debugging.rst | 2 ++
kernel/trace/trace.c | 10 ++++++++++
3 files changed, 14 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3872bc6ec49d6..0a60a60cf7a7b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6926,6 +6926,8 @@
This is just one of many ways that can clear memory. Make sure your system
keeps the content of memory across reboots before relying on this option.

+ NB: Both the mapped address and size must be page aligned for the architecture.
+
See also Documentation/trace/debugging.rst

diff --git a/Documentation/trace/debugging.rst b/Documentation/trace/debugging.rst
index 54fb16239d703..d54bc500af80b 100644
--- a/Documentation/trace/debugging.rst
+++ b/Documentation/trace/debugging.rst
@@ -136,6 +136,8 @@ kernel, so only the same kernel is guaranteed to work if the mapping is
preserved. Switching to a different kernel version may find a different
layout and mark the buffer as invalid.

+NB: Both the mapped address and size must be page aligned for the architecture.
+
Using trace_printk() in the boot instance
-----------------------------------------
By default, the content of trace_printk() goes into the top level tracing
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 13f817afba4c2..2f72d05570d04 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -10403,6 +10403,16 @@ __init static void enable_instances(void)
}

if (start) {
+ /* Start and size must be page aligned */
+ if (start & ~PAGE_MASK) {
+ pr_warn("Tracing: mapping start addr %pa is not page aligned\n", &start);
+ continue;
+ }
+ if (size & ~PAGE_MASK) {
+ pr_warn("Tracing: mapping size %pa is not page aligned\n", &size);
+ continue;
+ }
+
addr = map_pages(start, size);
if (addr) {
pr_info("Tracing: mapped boot instance %s at physical memory %pa of size 0x%lx\n",
--
2.39.5