linux-kernel - [PATCH v3 1/5] tracing: Enforce the persistent ring buffer to be page aligned

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Message-ID: <20250401203331.559044804@goodmis.org>
Date: Tue, 01 Apr 2025 16:25:50 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Vincent Donnefort <vdonnefort@...gle.com>,
 Vlastimil Babka <vbabka@...e.cz>,
 Mike Rapoport <rppt@...nel.org>,
 Jann Horn <jannh@...gle.com>
Subject: [PATCH v3 1/5] tracing: Enforce the persistent ring buffer to be page aligned

From: Steven Rostedt <rostedt@...dmis.org>

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/

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 Documentation/trace/debugging.rst               |  2 ++
 kernel/trace/trace.c                            | 12 ++++++++++++
 3 files changed, 16 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index fb8752b42ec8..71861643ef14 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7241,6 +7241,8 @@
 			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 54fb16239d70..d54bc500af80 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 14c38fcd6f9e..1288e0aaadf8 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -10774,6 +10774,18 @@ __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 %lx is not page aligned\n",
+					(unsigned long)start);
+				continue;
+			}
+			if (size & ~PAGE_MASK) {
+				pr_warn("Tracing: mapping size %lx is not page aligned\n",
+					(unsigned long)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",
-- 
2.47.2