linux-kernel - Re: [PATCH 02/11] x86: code shrink in paranoid

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Message-ID: <CALCETrWge6gKxZeVeFkVXtcHt8xByNXyGxhSjB7e9c1MWQLHKQ@mail.gmail.com>
Date:	Wed, 11 Feb 2015 12:36:36 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/11] x86: code shrink in paranoid_exit

On Wed, Jan 14, 2015 at 1:48 PM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> RESTORE_EXTRA_REGS + RESTORE_C_REGS looks small, but it's
> a lot of instructions (fourteen). Let's reuse them.
>
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Borislav Petkov <bp@...en8.de>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Frederic Weisbecker <fweisbec@...il.com>
> CC: X86 ML <x86@...nel.org>
> CC: Alexei Starovoitov <ast@...mgrid.com>
> CC: Will Drewry <wad@...omium.org>
> CC: Kees Cook <keescook@...omium.org>
> CC: linux-kernel@...r.kernel.org
> ---
>  arch/x86/kernel/entry_64.S | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index a21b5b3..f5e815e 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -1270,12 +1270,10 @@ ENTRY(paranoid_exit)
>         jnz paranoid_restore
>         TRACE_IRQS_IRETQ 0
>         SWAPGS_UNSAFE_STACK
> -       RESTORE_EXTRA_REGS
> -       RESTORE_C_REGS
> -       REMOVE_PT_GPREGS_FROM_STACK 8
> -       INTERRUPT_RETURN
> +       jmp paranoid_restore1
>  paranoid_restore:
>         TRACE_IRQS_IRETQ_DEBUG 0
> +paranoid_restore1:
>         RESTORE_EXTRA_REGS
>         RESTORE_C_REGS
>         REMOVE_PT_GPREGS_FROM_STACK 8

This is sort of a reply to the wrong thread, but wouldn't it be nicer
if we could pop a bunch of regs instead of using mov followed by add?
(Yes, this could be a followup, but it could be easier to spot now by
changing macros like RESTORE_XYZ.)

--Andy
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