From: Marcelo Tosatti <mtosatti@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: "Zhang, Yang Z" <yang.z.zhang@intel.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"Shan, Haitao" <haitao.shan@intel.com>,
"Zhang, Xiantao" <xiantao.zhang@intel.com>,
"Nakajima, Jun" <jun.nakajima@intel.com>,
"Anvin, H Peter" <h.peter.anvin@intel.com>
Subject: Re: [PATCH 2/2] x86, apicv: Add Posted Interrupt supporting
Date: Mon, 4 Feb 2013 17:59:52 -0200 [thread overview]
Message-ID: <20130204195952.GA15856@amt.cnet> (raw)
In-Reply-To: <20130204171301.GB10756@redhat.com>
On Mon, Feb 04, 2013 at 07:13:01PM +0200, Gleb Natapov wrote:
> On Mon, Feb 04, 2013 at 12:43:45PM -0200, Marcelo Tosatti wrote:
> > > > Any example how software relies on such two-interrupts-queued-in-IRR/ISR behaviour?
> > > Don't know about guests, but KVM relies on it to detect interrupt
> > > coalescing. So if interrupt is set in IRR but not in PIR interrupt will
> > > not be reported as coalesced, but it will be coalesced during PIR->IRR
> > > merge.
> >
> > Yes, so:
> >
> > 1. IRR=1, ISR=0, PIR=0. Event: set_irq, coalesced=no.
> > 2. IRR=0, ISR=1, PIR=0. Event: IRR->ISR transfer.
> > 3. vcpu outside of guest mode.
> > 4. IRR=1, ISR=1, PIR=0. Event: set_irq, coalesced=no.
> > 5. vcpu enters guest mode.
> > 6. IRR=1, ISR=1, PIR=1. Event: set_irq, coalesced=no.
> > 7. HW transfers PIR into IRR.
> >
> > set_irq return value at 7 is incorrect, interrupt event was _not_
> > queued.
> Not sure I understand the flow of events in your description correctly. As I
> understand it at 4 set_irq() will return incorrect result. Basically
> when PIR is set to 1 while IRR has 1 for the vector the value of
> set_irq() will be incorrect.
At 4 it has not been coalesced: it has been queued to IRR.
At 6 it has been coalesced: PIR bit merged into IRR bit.
> Frankly I do not see how it can be fixed
> without any race with present HW PIR design.
At kvm_accept_apic_interrupt, check IRR before setting PIR bit, if IRR
already set, don't set PIR.
next prev parent reply other threads:[~2013-02-04 21:40 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-13 7:29 [PATCH 0/2] KVM: Add posted interrupt supporting Yang Zhang
2012-12-13 7:29 ` [PATCH 1/2] x86: Enable ack interrupt on vmexit Yang Zhang
2012-12-13 7:51 ` Gleb Natapov
2012-12-13 7:54 ` Zhang, Yang Z
2012-12-13 7:58 ` Gleb Natapov
2012-12-13 8:03 ` Zhang, Yang Z
2012-12-13 8:05 ` Gleb Natapov
2012-12-13 8:19 ` Zhang, Yang Z
2012-12-13 8:22 ` Gleb Natapov
2012-12-13 8:23 ` Zhang, Yang Z
2012-12-16 13:26 ` Zhang, Yang Z
2012-12-18 9:11 ` Gleb Natapov
2012-12-13 7:29 ` [PATCH 2/2] x86, apicv: Add Posted Interrupt supporting Yang Zhang
2013-01-22 22:59 ` Marcelo Tosatti
2013-01-23 5:09 ` Zhang, Yang Z
2013-01-24 23:43 ` Marcelo Tosatti
2013-01-25 0:40 ` Zhang, Yang Z
2013-01-30 23:03 ` Marcelo Tosatti
2013-01-30 23:57 ` Marcelo Tosatti
2013-01-31 7:35 ` Gleb Natapov
2013-01-31 9:43 ` Gleb Natapov
2013-01-31 13:32 ` Marcelo Tosatti
2013-01-31 13:38 ` Gleb Natapov
2013-01-31 13:44 ` Marcelo Tosatti
2013-01-31 13:55 ` Gleb Natapov
2013-02-04 0:57 ` Marcelo Tosatti
2013-02-04 9:10 ` Zhang, Yang Z
2013-02-04 9:55 ` Gleb Natapov
2013-02-04 14:43 ` Marcelo Tosatti
2013-02-04 17:13 ` Gleb Natapov
2013-02-04 19:59 ` Marcelo Tosatti [this message]
2013-02-04 20:47 ` Marcelo Tosatti
2013-02-05 5:57 ` Zhang, Yang Z
2013-02-05 8:00 ` Gleb Natapov
2013-02-05 10:35 ` Zhang, Yang Z
2013-02-05 10:54 ` Gleb Natapov
2013-02-05 10:58 ` Zhang, Yang Z
2013-02-05 11:16 ` Gleb Natapov
2013-02-05 13:26 ` Zhang, Yang Z
2013-02-05 13:29 ` Gleb Natapov
2013-02-05 13:40 ` Zhang, Yang Z
2013-02-05 13:43 ` Gleb Natapov
2013-02-07 1:23 ` Marcelo Tosatti
2013-02-05 7:32 ` Gleb Natapov
2013-02-06 22:49 ` Marcelo Tosatti
2013-02-07 0:24 ` Marcelo Tosatti
2013-02-07 13:52 ` Gleb Natapov
2013-02-08 2:07 ` Marcelo Tosatti
2013-02-08 12:18 ` Gleb Natapov
2013-02-07 14:01 ` Gleb Natapov
2013-02-07 21:49 ` Marcelo Tosatti
2013-02-08 12:28 ` Gleb Natapov
2013-02-08 13:46 ` Marcelo Tosatti
2013-01-31 9:37 ` Gleb Natapov
2013-02-04 9:11 ` Zhang, Yang Z
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