Re: [PATCH] KVM: nVMX: Fix loss of pending event before entering L2

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2018-08-29 09:34-0700, Sean Christopherson:
> On Wed, Aug 29, 2018 at 06:18:20PM +0200, Radim Krčmář wrote:
> > 2018-08-29 18:43+0300, Liran Alon:
> > > Consider the case L1 had a pending event until it executed
> > > VMLAUNCH/VMRESUME which wasn't delivered because it was disallowed
> > > (e.g. interrupts disabled). When L1 executes VMLAUNCH/VMRESUME,
> > > L0 needs to evaluate if this pending event should cause an exit from
> > > L2 to L1 or delivered directly to L2 (In case L1 don't intercept
> > > EXTERNAL_INTERRUPT).
> > > 
> > > Usually this would be handled by L0 requesting a window (e.g. IRQ
> > > window) by setting VMCS accordingly. However, this setting was done on
> > > VMCS01 and now VMCS02 is active instead. Thus, when L1 executes
> > > VMLAUNCH/VMRESUME we force L0 to perform pending event evaluation by
> > > requesting a KVM_REQ_EVENT.
> > > 
> > > Note that above scenario exists when L1 KVM is about to enter L2 but
> > > requests an "immediate-exit". As in this case, L1 will
> > > disable-interrupts and then send a self-IPI before entering L2.
> > 
> > Which makes it a big blunder, I'll add "Cc: stable@xxxxxxxxxxxxxxx".
> 
> Please hold off on doing anything with this, I don't think this is the
> correct fix.  I have a half-finished response to the preemption timer
> thread that prompted this patch, I'll get that sent ASAP. 

Sure, thanks for the heads-up.



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