linux-kernel - Re: [PATCH] x86: vdso32/syscall.S: do not load __USER32

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Message-ID: <CALCETrW4n_PD=Y=Ozf8FGCHk_-+zvHHYCMXRTr4BmMG85ddQrQ@mail.gmail.com>
Date:	Mon, 23 Mar 2015 12:37:20 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
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] x86: vdso32/syscall.S: do not load __USER32_DS to %ss

On Mon, Mar 23, 2015 at 9:47 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> This vDSO code only gets used by 64-bit kernel,
> not 32-bit. In 64-bit kernels, data segment is the same
> for 32-bit and 64-bit userspace, and SYSRET insn does load %ss
> with its selector. No need to repeat it by hand. Segment loads
> are somewhat expensive: tens of cycles.
>
> 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
> ---
>
> Patch was run-tested.

Applied, thanks.

--Andy
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