Messages in this thread | | | Date | Wed, 2 Mar 2016 14:24:29 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH 03/10] x86/entry/32: Filter NT and speed up AC filtering in SYSENTER |
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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 <luto@kernel.org> > --- > 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.
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