linux-kernel - Re: [PATCH v2 2/7] x86/entry/32: Simplify common

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Date:   Wed, 10 Jul 2019 16:11:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, bp@...en8.de, mingo@...nel.org,
        luto@...nel.org, torvalds@...ux-foundation.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, jgross@...e.com,
        linux-kernel@...r.kernel.org, zhe.he@...driver.com,
        joel@...lfernandes.org, devel@...ukata.com
Subject: Re: [PATCH v2 2/7] x86/entry/32: Simplify common_exception

On Thu, 04 Jul 2019 21:55:57 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -294,9 +294,11 @@
>  .Lfinished_frame_\@:
>  .endm
>  
> -.macro SAVE_ALL pt_regs_ax=%eax switch_stacks=0
> +.macro SAVE_ALL pt_regs_ax=%eax switch_stacks=0 skip_gs=0
>  	cld
> +.if \skip_gs == 0
>  	PUSH_GS
> +.endif
>  	FIXUP_FRAME
>  	pushl	%fs
>  	pushl	%es
> @@ -313,13 +315,13 @@
>  	movl	%edx, %es
>  	movl	$(__KERNEL_PERCPU), %edx
>  	movl	%edx, %fs
> +.if \skip_gs == 0
>  	SET_KERNEL_GS %edx
> -
> +.endif
>  	/* Switch to kernel stack if necessary */
>  .if \switch_stacks > 0
>  	SWITCH_TO_KERNEL_STACK
>  .endif
> -
>  .endm
>  
>  .macro SAVE_ALL_NMI cr3_reg:req
> @@ -1448,32 +1450,20 @@ END(page_fault)
>  
>  common_exception:
>  	/* the function address is in %gs's slot on the stack */
> -	FIXUP_FRAME
> -	pushl	%fs
> -	pushl	%es
> -	pushl	%ds
> -	pushl	%eax
> -	movl	$(__USER_DS), %eax
> -	movl	%eax, %ds
> -	movl	%eax, %es
> -	movl	$(__KERNEL_PERCPU), %eax
> -	movl	%eax, %fs
> -	pushl	%ebp
> -	pushl	%edi
> -	pushl	%esi
> -	pushl	%edx
> -	pushl	%ecx
> -	pushl	%ebx
> -	SWITCH_TO_KERNEL_STACK
> +	SAVE_ALL switch_stacks=1 skip_gs=1
>  	ENCODE_FRAME_POINTER
> -	cld

The only code change of this is that cld moved from the end to the
beginning. As this appears to match other SAVE_ALL users with respect
to ENCODE_FRAME_POINTER, this shouldn't be an issue.

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve



>  	UNWIND_ESPFIX_STACK
> +