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SubjectRe: [PATCH] x86: vdso32/syscall.S: do not load __USER32_DS to %ss
On Mon, Mar 23, 2015 at 12:37 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Mon, Mar 23, 2015 at 9:47 AM, Denys Vlasenko <dvlasenk@redhat.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@redhat.com>
>> CC: Linus Torvalds <torvalds@linux-foundation.org>
>> CC: Steven Rostedt <rostedt@goodmis.org>
>> CC: Ingo Molnar <mingo@kernel.org>
>> CC: Borislav Petkov <bp@alien8.de>
>> CC: "H. Peter Anvin" <hpa@zytor.com>
>> CC: Andy Lutomirski <luto@amacapital.net>
>> CC: Oleg Nesterov <oleg@redhat.com>
>> CC: Frederic Weisbecker <fweisbec@gmail.com>
>> CC: Alexei Starovoitov <ast@plumgrid.com>
>> CC: Will Drewry <wad@chromium.org>
>> CC: Kees Cook <keescook@chromium.org>
>> CC: x86@kernel.org
>> CC: linux-kernel@vger.kernel.org
>> ---
>>
>> Patch was run-tested.
>
> Applied, thanks.

Actually, I want to remove the added comment in the code. I don't see
why we should have a specific comment about SS and not about, say, CS,
ESP, or anything else. OK?

>
> --Andy



--
Andy Lutomirski
AMA Capital Management, LLC


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