On 11/03/2014 01:11 PM, Andy Lutomirski wrote: > On Tue, Oct 28, 2014 at 4:14 AM, tip-bot for Andy Lutomirski > <tipbot@xxxxxxxxx> wrote: >> Commit-ID: 2c7577a7583747c9b71f26dced7f696b739da745 >> Gitweb: http://git.kernel.org/tip/2c7577a7583747c9b71f26dced7f696b739da745 >> Author: Andy Lutomirski <luto@xxxxxxxxxxxxxx> >> AuthorDate: Wed, 1 Oct 2014 11:28:25 -0700 >> Committer: Ingo Molnar <mingo@xxxxxxxxxx> >> CommitDate: Tue, 28 Oct 2014 11:11:30 +0100 >> >> sched/x86_64: Don't save flags on context switch >> >> Now that the kernel always runs with clean flags (in particular, >> NT is clear), there is no need to save and restore flags on >> every context switch. > > Just to make myself a little more comfortable with this... > > There is one potentially relevant flag: AC. I think this is still OK. > If we schedule with STAC set, then we've already screwed up, I think. > Even preempt schedules from interrupt context, so if we schedule due > to preemption or #PF in the middle of uaccess, AC should be saved and > cleared by whatever interrupt caused the reschedule, right? > > And do we ever have TF set during a context switch? I hope not. > > Also, what's with 'jmp exit_intr' at the end of retint_kernel? Why > isn't that 'jmp retint_kernel'? > AC is saved by interrupts and cleared by IRET. We execute CLAC in all the interrupt entry paths. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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