fgraph: Separate size of ret_stack from PAGE_SIZE

[PATCH] fgraph: Separate size of ret_stack from PAGE_SIZE

Posted by Steven Rostedt 1 month, 1 week ago

From: Steven Rostedt <rostedt@goodmis.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@arm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 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				\
-- 
2.45.2

Re: [PATCH] fgraph: Separate size of ret_stack from PAGE_SIZE

Posted by Masami Hiramatsu (Google) 1 month ago

On Sat, 19 Oct 2024 15:29:51 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Steven Rostedt <rostedt@goodmis.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/
>

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks!
 
> Suggested-by: Ryan Roberts <ryan.roberts@arm.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  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				\
> -- 
> 2.45.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH] fgraph: Separate size of ret_stack from PAGE_SIZE

Posted by Ryan Roberts 1 month ago

On 19/10/2024 20:29, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.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@arm.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

LGTM!

Reviewed-by: Ryan Roberts <ryan.roberts@arm.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				\