linux-kernel - Re: [PATCHv5 5/5] kvm: host side for eoi optimization

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Date:	Thu, 31 May 2012 17:52:20 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	x86@...nel.org, kvm@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv5 5/5] kvm: host side for eoi optimization

On Thu, May 31, 2012 at 01:15:13PM +0300, Gleb Natapov wrote:
> > > > +	    /* Cache not set: safe but we don't bother. */
> > > > +	    unlikely(apic->isr_cache == -1) ||
> > > > +	    /* Need EOI to update ioapic. */
> > > > +	    unlikely(kvm_ioapic_handles_vector(vcpu->kvm, apic->isr_cache)))
> > > > +		return;
> > > > +
> > > > +	pv_eoi_set_pending(apic->vcpu);
> > > > +}
> > > > +
> > > apic_sync_pv_eoi_to_guest() is not paired with
> > > apic_sync_pv_eoi_from_guest() if event injection is canceled.
> > > You can enter guest with stale pv_eoi bit.
> > 
> > Never. The pv_eoi bit is cleared on each exit.
> There will be no exit since there will be no entry. Search for
> "goto out" after kvm_lapic_sync_to_vapic().

I think you've found a bug, thanks a bunch.
I have fixed it but the x86 guys asked me not to
post more patches until merge window closes :(
So I'll sit on a fix for several days.
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