linux-kernel - Re: [PATCH 04/24] x86/entry: Expose the address of .Lgs

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Date:   Thu, 2 Sep 2021 11:14:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 04/24] x86/entry: Expose the address of .Lgs_change to
 traps.c

On Wed, Sep 01, 2021 at 01:50:05AM +0800, Lai Jiangshan wrote:

> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index e38a4cf795d9..9164e85b36b8 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -729,6 +729,7 @@ _ASM_NOKPROBE(common_interrupt_return)
>  SYM_FUNC_START(asm_load_gs_index)
>  	FRAME_BEGIN
>  	swapgs
> +SYM_INNER_LABEL(asm_load_gs_index_gs_change, SYM_L_GLOBAL)
>  .Lgs_change:

After all the patches, there's only a single .Lgs_change reference left.
Can't we convert the _ASM_EXTABLE() entry to use the new label and
totally remove it?

>  	movl	%edi, %gs
>  2:	ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
> @@ -1011,7 +1012,7 @@ SYM_CODE_START_LOCAL(error_entry)
>  	movl	%ecx, %eax			/* zero extend */
>  	cmpq	%rax, RIP+8(%rsp)
>  	je	.Lbstep_iret
> -	cmpq	$.Lgs_change, RIP+8(%rsp)
> +	cmpq	$asm_load_gs_index_gs_change, RIP+8(%rsp)
>  	jne	.Lerror_entry_done_lfence