linux-kernel - Re: [PATCH] kvm: dont clear TMR on EOI

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Message-ID: <20120412114955.GI20431@redhat.com>
Date:	Thu, 12 Apr 2012 14:49:55 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: dont clear TMR on EOI

On Wed, Apr 11, 2012 at 11:03:18PM -0300, Marcelo Tosatti wrote:
> On Wed, Apr 11, 2012 at 06:49:55PM +0300, Michael S. Tsirkin wrote:
> > Intel spec says that TMR needs to be set/cleared
> > when IRR is set, but kvm also clears it on  EOI.
> > 
> > I did some tests on a real (AMD based) system,
> > and I see same TMR values both before
> > and after EOI, so I think it's a minor bug in kvm.
> > 
> > This patch fixes TMR to be set/cleared on IRR set
> > only as per spec.
> > 
> > And now that we don't clear TMR, we can save
> > an atomic read of TMR on EOI that's not propagated
> > to ioapic, by checking whether ioapic needs
> > a specific vector first and calculating
> > the mode afterwards.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> >  arch/x86/kvm/lapic.c |   19 +++++++++++++------
> >  virt/kvm/ioapic.c    |   10 +++++++---
> >  virt/kvm/ioapic.h    |    1 +
> >  3 files changed, 21 insertions(+), 9 deletions(-)
> 
> Looks OK, ioapic_service -> accept_apic_irq will set TMR 
> again if IRR is raised. Gleb, can you review please?
> 
Looks good to me.

--
			Gleb.
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