linux-kernel - Re: [PATCH] fgraph: Separate size of ret_stack from PAGE

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Message-ID: <218a79b3-8bf1-4a2a-a137-092920830b91@arm.com>
Date: Mon, 21 Oct 2024 09:01:25 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Steven Rostedt <rostedt@...dmis.org>, LKML
 <linux-kernel@...r.kernel.org>,
 Linux trace kernel <linux-trace-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] fgraph: Separate size of ret_stack from PAGE_SIZE

On 19/10/2024 20:29, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@...dmis.org>
> 
> The ret_stack (shadow stack used by function graph infrastructure) is
> currently defined as PAGE_SIZE. But some architectures which have 64K
> PAGE_SIZE, this is way overkill. Also there's an effort to allow the
> PAGE_SIZE to be defined at boot up.
> 
> Hard code it for now to 4096. In the future, this size may change and even
> be dependent on specific architectures.
> 
> Link: https://lore.kernel.org/all/e5067bb8-0fcd-4739-9bca-0e872037d5a1@arm.com/
> 
> Suggested-by: Ryan Roberts <ryan.roberts@....com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>

LGTM!

Reviewed-by: Ryan Roberts <ryan.roberts@....com>

> ---
>  kernel/trace/fgraph.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index ee829d65f301..51e81b299a0d 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -153,7 +153,7 @@ enum {
>   * SHADOW_STACK_OFFSET:	The size in long words of the shadow stack
>   * SHADOW_STACK_MAX_OFFSET: The max offset of the stack for a new frame to be added
>   */
> -#define SHADOW_STACK_SIZE	(PAGE_SIZE)
> +#define SHADOW_STACK_SIZE	(4096)
>  #define SHADOW_STACK_OFFSET	(SHADOW_STACK_SIZE / sizeof(long))
>  /* Leave on a buffer at the end */
>  #define SHADOW_STACK_MAX_OFFSET				\