On Mon, Oct 12, 2015 at 1:48 PM, Denys Vlasenko <dvlas...@redhat.com> wrote: > On 10/09/2015 09:48 PM, Andy Lutomirski wrote: >> Anyway, it's still a win, but I'll keep playing. There may be even >> better ways to do this. > > Such as this? > Drop OR, check for cleared IF here: > > testl $X86_EFLAGS_NT, EFLAGS(%rsp) > jnz sysenter_fix_flags > testl $X86_EFLAGS_IF, EFLAGS(%rsp) > jz sysenter_fix_flags > sysenter_flags_fixed: > > and make sysenter_fix_flags code set IF in addition to TF clearing. > This way, we don't even have an unconditional RMW op.
IF should normally be set in userspace, but since SYSENTER doesn't save the old flags and always clears IF when entering the kernel, the flags pushed on the stack will always have IF clear. -- Brian Gerst -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
