linux-kernel - Re: [PATCH v4 12/17] x86/asm/entry/64: Save all regs on interrupt entry

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Date:	Thu, 2 Jul 2015 12:52:58 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v4 12/17] x86/asm/entry/64: Save all regs on interrupt
 entry

On Mon, Jun 29, 2015 at 12:33:44PM -0700, Andy Lutomirski wrote:
> To prepare for the big rewrite of the error and interrupt exit
> paths, we will need pt_regs completely filled in.  It's already
> completely filled in when error_exit runs, so rearrange interrupt
> handling to match it.  This will slow down interrupt handling very
> slightly (eight instructions), but the simplification it enables
> will be more than worth it.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/entry/entry_64.S | 29 +++++++++--------------------
>  1 file changed, 9 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 9bc76766aa71..51d34fafe4c0 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -502,21 +502,13 @@ END(irq_entries_start)
>  /* 0(%rsp): ~(interrupt number) */
>  	.macro interrupt func
>  	cld
> -	/*
> -	 * Since nothing in interrupt handling code touches r12...r15 members
> -	 * of "struct pt_regs", and since interrupts can nest, we can save
> -	 * four stack slots and simultaneously provide
> -	 * an unwind-friendly stack layout by saving "truncated" pt_regs
> -	 * exactly up to rbp slot, without these members.
> -	 */
> -	ALLOC_PT_GPREGS_ON_STACK -RBP
> -	SAVE_C_REGS -RBP
> -	/* this goes to 0(%rsp) for unwinder, not for saving the value: */
> -	SAVE_EXTRA_REGS_RBP -RBP

That macro's unused now AFAICT.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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