Re: [PATCH v6 04/15] x86/pvh: Use fixed_percpu_data for early boot GSBASE

[Mateusz Guzik]

On Thu, Jan 23, 2025 at 02:07:36PM -0500, Brian Gerst wrote:
> Instead of having a private area for the stack canary, use
> fixed_percpu_data for GSBASE like the native kernel.
> 
> Signed-off-by: Brian Gerst <brgerst@xxxxxxxxx>
> Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
>  arch/x86/platform/pvh/head.S | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
> index 4733a5f467b8..fa0072e0ca43 100644
> --- a/arch/x86/platform/pvh/head.S
> +++ b/arch/x86/platform/pvh/head.S
> @@ -173,10 +173,15 @@ SYM_CODE_START(pvh_start_xen)
>  1:
>  	UNWIND_HINT_END_OF_STACK
>  
> -	/* Set base address in stack canary descriptor. */
> -	mov $MSR_GS_BASE,%ecx
> -	leal canary(%rip), %eax
> -	xor %edx, %edx
> +	/*
> +	 * Set up GSBASE.
> +	 * Note that, on SMP, the boot cpu uses init data section until
> +	 * the per cpu areas are set up.
> +	 */
> +	movl $MSR_GS_BASE,%ecx
> +	leaq INIT_PER_CPU_VAR(fixed_percpu_data)(%rip), %rdx
> +	movq %edx, %eax

	movl

I'm bisecting perf breakage and landing on this commit breaks the build.