From: Gleb Natapov <gleb@redhat.com>
To: Marcelo Tosatti <mtosatti@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 19:13:01 +0200 [thread overview]
Message-ID: <20130204171301.GB10756@redhat.com> (raw)
In-Reply-To: <20130204144345.GA11328@amt.cnet>
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. Frankly I do not see how it can be fixed
without any race with present HW PIR design.
--
Gleb.
next prev parent reply other threads:[~2013-02-04 17:13 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 [this message]
2013-02-04 19:59 ` Marcelo Tosatti
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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