Re: [Xen-devel] [PATCH] x86/boot: Disable IBRS in intr/nmi exit path at bootup stage

[Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>]

在 2018/3/26 21:39, Jan Beulich 写道:
> > > > On 21.03.18 at 03:58, <zhenzhong.duan@xxxxxxxxxx> wrote:
> > After reset, IBRS is disabled by processor, but a coming intr/nmi leave IBRS
> > enabled after their exit. It's not necessory for bootup code to run in low
> > performance with IBRS enabled.
> >
> > On ORACLE X6-2(500GB/88 cpus, dom0 11GB/20 vcpus), we observed an 200s+ delay
> > in construct_dom0.
> >
> > By initializing use_shadow_spec_ctrl with 1, IBRS is disabled in intr/nmi exit
> > path at bootup stage. Then delay in construct_dom0 is ~50s.
> While I can certainly follow the argumentation, did you pay
> attention to Andrew also modifying what you would call "bootup
> code" in commit 7c508612f7 ("x86: Support indirect thunks from
> assembly code")? That wasn't just a random change - we
> specifically want it for the case of bringing up CPUs at runtime.
> You'll need to be equally careful here, I think: Rather than
> storing literal 1 (which should have been "true" anyway), you'll
> want to store (system_state < SYS_STATE_active) or maybe
> (system_state != SYS_STATE_active), at least when the CPU
> being booted is a hyperthread of a CPU which is active already.
Make sense for me, thank you for explanation. I'll send a new patch.

Regards
Zhenzhong

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