Re: [PATCH] x86: vdso32/syscall.S: do not load __USER32_DS to %ss

[Andy Lutomirski]

On Mon, Mar 23, 2015 at 12:37 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Mon, Mar 23, 2015 at 9:47 AM, Denys Vlasenko <dvlasenk@xxxxxxxxxx> 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@xxxxxxxxxx>
>> CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>> CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
>> CC: Ingo Molnar <mingo@xxxxxxxxxx>
>> CC: Borislav Petkov <bp@xxxxxxxxx>
>> CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
>> CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> CC: Oleg Nesterov <oleg@xxxxxxxxxx>
>> CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
>> CC: Alexei Starovoitov <ast@xxxxxxxxxxxx>
>> CC: Will Drewry <wad@xxxxxxxxxxxx>
>> CC: Kees Cook <keescook@xxxxxxxxxxxx>
>> CC: x86@xxxxxxxxxx
>> CC: linux-kernel@xxxxxxxxxxxxxxx
>> ---
>>
>> 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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