Re: [PATCH v5 1/4] tracing: Enforce the persistent ring buffer to be page aligned

[Mike Rapoport <rppt@kernel.org>]

On Tue, Apr 01, 2025 at 06:58:12PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.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@linux-foundation.org>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.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 3435a062a208..f904fd8481bd 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -7266,6 +7266,8 @@
>  			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 de6d7f0e6206..de9c237e5826 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -10788,6 +10788,18 @@ __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;
> +			}

Better use %pa for printing physical address as on 32-bit systems
phys_addr_t may be unsigned long long:

	pr_warn("Tracing: mapping size %pa is not page aligned\n", &size);

> +
>  			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
> 
> 

-- 
Sincerely yours,
Mike.