linux-kernel - Re: [PATCH v1 1/8] x86/entry/clearregs: Remove partial stack frame in fast system call

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Message-ID: <20180111020916.2pionyjrik6pdwzb@treble>
Date:   Wed, 10 Jan 2018 20:09:16 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, dwmw@...zon.co.uk, pjt@...gle.com,
        luto@...nel.org, peterz@...radead.org, thomas.lendacky@....com,
        tim.c.chen@...ux.intel.com, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, jikos@...nel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v1 1/8] x86/entry/clearregs: Remove partial stack frame
 in fast system call

On Tue, Jan 09, 2018 at 05:03:21PM -0800, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> Remove the partial stack frame in the 64bit syscall fast path.
> In the next patch we want to clear the extra registers, which requires
> to always save all registers. So remove the partial stack frame
> in the syscall fast path and always save everything.
> 
> This actually simplifies the code because the ptregs stubs
> are not needed anymore.
> 
> arch/x86/entry/entry_64.S   | 57 ++++-----------------------------------------------------
> arch/x86/entry/syscall_64.c |  2 +-
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/entry/entry_64.S   | 57 ++++-----------------------------------------
>  arch/x86/entry/syscall_64.c |  2 +-
>  2 files changed, 5 insertions(+), 54 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 58dbf7a12a05..bbdfbdd817d6 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -234,7 +234,9 @@ GLOBAL(entry_SYSCALL_64_after_hwframe)
>  	pushq	%r9				/* pt_regs->r9 */
>  	pushq	%r10				/* pt_regs->r10 */
>  	pushq	%r11				/* pt_regs->r11 */
> -	sub	$(6*8), %rsp			/* pt_regs->bp, bx, r12-15 not saved */
> +	sub	$(6*8), %rsp
> +	SAVE_EXTRA_REGS
> +
>  	UNWIND_HINT_REGS extra=0

Now that the extra regs are being saved, the "extra=0" can be removed
from the unwind hint.

-- 
Josh