Re: [RFC][PATCH 3/3] x86/entry, ORC: Teach objtool/unwind_orc about stack irq swizzles

From: Peter Zijlstra
Date: Fri May 08 2020 - 09:21:41 EST


On Fri, May 08, 2020 at 02:26:32PM +0200, Thomas Gleixner wrote:
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
>
> > On Thu, May 07, 2020 at 11:24:49PM +0200, Thomas Gleixner wrote:
> >> But over our IRC conversation I came up with a 3rd variant:
> >>
> >> For most of the vectors the indirect call overhead is just noise, so
> >> we can run them through the ASM switcher, but for the resched IPI
> >> we can just use a separate direct call stub in ASM.
> >
> > Are we sure the rat-poison crap is noise for all the other system
> > vectors? I suppose it is for most since they'll do indirect calls
> > themselves anyway, right?
>
> We have different categories:
>
> 1) Uninteresting
>
> SPURIOUS_APIC_VECTOR, ERROR_APIC_VECTOR, THERMAL_APIC_VECTOR,
> THRESHOLD_APIC_VECTOR, REBOOT_VECTOR, DEFERRED_ERROR_VECTOR
>
> 2) Indirect call poisoned
>
> LOCAL_TIMER_VECTOR
> X86_PLATFORM_IPI_VECTOR
> IRQ_WORK_VECTOR
> HYPERV_STIMER0_VECTOR
> HYPERVISOR_CALLBACK_VECTOR
> POSTED_INTERRUPT_WAKEUP_VECTOR.
> CALL_FUNCTION_VECTOR
> CALL_FUNCTION_SINGLE_VECTOR
>
> 3) Quick
>
> RESCHEDULE_VECTOR
>
> POSTED_INTR_VECTOR
> POSTED_INTR_NESTED_VECTOR
>
> These two postit ones are weird because they are both empty and
> just increment different irq counts.
>
> HYPERV_REENLIGHTENMENT_VECTOR
>
> schedules delayed work, i,e. arms a timer which should be
> straight forward, but does it matter?
>
> 4) Others
>
> UV_BAU_MESSAGE - The TLB flushes are probably more expensive than
> ratpoutine
>
> Hmm?

As we just agreed on IRC, 3) can run without changing stack, and then
the rest can use the indirect thing.