Re: [PATCH 4/5] x86/entry_64.S: get rid of FIXUP_TOP_OF_STACK/RESTORE_TOP_OF_STACK

[Borislav Petkov]

On Thu, Mar 19, 2015 at 06:17:48PM +0100, Denys Vlasenko wrote:
> FIXUP_TOP_OF_STACK is only necessary because we don't save %r11
> to pt_regs->r11 on SYSCALL64 fast path, but we want ptrace to see
> it populated.
> 
> Bite the bullet, add a single additional PUSH insn, and remove
> FIXUP_TOP_OF_STACK.
> 
> RESTORE_TOP_OF_STACK is already a nop. Remove it too.
> 
> On SandyBridge CPU, it does not get slower:
> measured 54.22 ns per getpid syscall before and after last two changes
> on defconfig kernel.
> 
> 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
> ---
>  arch/x86/kernel/entry_64.S | 35 ++---------------------------------
>  1 file changed, 2 insertions(+), 33 deletions(-)

Nice diffstat.

Acked-by: Borislav Petkov <bp@xxxxxxx>

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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