On Sun, Feb 28, 2016 at 09:28:48PM -0800, Andy Lutomirski wrote:
> This makes the 32-bit code work just like the 64-bit code. It should
> speed up syscalls on 32-bit kernels on Skylake by something like 20
> cycles (by analogy to the 64-bit compat case).
>
> It also cleans up NT just like we do for the 64-bit case.
>
> Signed-off-by: Andy Lutomirski <[email protected]>
> ---
> arch/x86/entry/entry_32.S | 23 ++++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> index ab710eee4308..263ebde6333f 100644
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -294,7 +294,6 @@ sysenter_past_esp:
> pushl $__USER_DS /* pt_regs->ss */
> pushl %ebp /* pt_regs->sp (stashed in bp) */
> pushfl /* pt_regs->flags (except IF = 0) */
> - ASM_CLAC /* Clear AC after saving FLAGS */
> orl $X86_EFLAGS_IF, (%esp) /* Fix IF */
> pushl $__USER_CS /* pt_regs->cs */
> pushl $0 /* pt_regs->ip = 0 (placeholder) */
> @@ -302,6 +301,23 @@ sysenter_past_esp:
> SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest */
>
> /*
> + * Sysenter doesn't filter flags, so we need to clear NT and AC
> + * ourselves. To save a few cycles, we can check whether
> + * either was set instead of doing an unconditional popfq.
Let's write insn names capitalized: SYSENTER, POPF, etc... I know,
entry_SYSENTER_compat() doesn't do it either but you could fix that up
in your 2/10 patch, since you're touching that place anyway...
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
