Re: [PATCH] x86/static_call: Fix __static_call_fixup()

[Josh Poimboeuf]

On Wed, Aug 16, 2023 at 01:08:09AM +0200, Peter Zijlstra wrote:
>  bool __static_call_fixup(void *tramp, u8 op, void *dest)
>  {
> +	/*
> +	 * Not all .return_sites are a static_call trampoline (most are not).
> +	 * Check if the next 3 bytes are still kernel text, if not, then this

s/3/7 ?

> +	 * definitely is not a trampoline and we need not worry further.
> +	 *
> +	 * This avoids the memcmp() below tripping over pagefaults etc..
> +	 */
> +	if (!kernel_text_address(tramp+7))
> +		return false;
> +
>  	if (memcmp(tramp+5, tramp_ud, 3)) {
>  		/* Not a trampoline site, not our problem. */
>  		return false;

kernel_text_address() can be quite heavyweight to call in a loop during
module loading.  Maybe that doesn't matter much.  But it would be a lot
faster to only call kernel_text_address() if tramp+7 is on the next
page.

-- 
Josh