linux-kernel - Re: [PATCH 3/3] x86: do not save callee-preserved registers around lockdep_sys_exit

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Message-ID: <CALCETrVTU7Ji9UOdEnBH7pjKOGLFh1+DXQCo69HGs+ZFEkPa6A@mail.gmail.com>
Date:	Sun, 1 Mar 2015 08:16:18 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] x86: do not save callee-preserved registers around lockdep_sys_exit_thunk

On Fri, Feb 27, 2015 at 4:29 PM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> Internally, lockdep_sys_exit_thunk saves callee-clobbered registers,
> and calls a C function, lockdep_sys_exix. Thus, callee-preserved
> won't be mangled, there is no need to save them.
>
> Patch was run-tested.

Peterz, I think this was your code.

--Andy

>
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Ingo Molnar <mingo@...nel.org>
> CC: Borislav Petkov <bp@...en8.de>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Frederic Weisbecker <fweisbec@...il.com>
> CC: Alexei Starovoitov <ast@...mgrid.com>
> CC: Will Drewry <wad@...omium.org>
> CC: Kees Cook <keescook@...omium.org>
> CC: x86@...nel.org
> CC: linux-kernel@...r.kernel.org
> ---
>  arch/x86/include/asm/irqflags.h | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
> index 19355f3..9a63eae 100644
> --- a/arch/x86/include/asm/irqflags.h
> +++ b/arch/x86/include/asm/irqflags.h
> @@ -179,9 +179,7 @@ static inline int arch_irqs_disabled(void)
>  #    define LOCKDEP_SYS_EXIT_IRQ \
>         TRACE_IRQS_ON; \
>         sti; \
> -       SAVE_EXTRA_REGS; \
>         call lockdep_sys_exit_thunk; \
> -       RESTORE_EXTRA_REGS; \
>         cli; \
>         TRACE_IRQS_OFF;
>  #  else
> --
> 1.8.1.4
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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