From: Paul Durrant <Paul.Durrant@citrix.com>
To: Paul Durrant <Paul.Durrant@citrix.com>,
'Jan Beulich' <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
"osstest-admin@xenproject.org" <osstest-admin@xenproject.org>
Subject: Re: [xen-unstable test] 118078: regressions - FAIL
Date: Wed, 17 Jan 2018 10:17:47 +0000 [thread overview]
Message-ID: <66a1c061ec3443a8b8dbeed30a29be8a@AMSPEX02CL01.citrite.net> (raw)
In-Reply-To: <7404c0002a66413ca96bb2409ae70ad6@AMSPEX02CL01.citrite.net>
> -----Original Message-----
[snip]
> What I meant was that I'd expect the guest to have interrupts disabled whilst
> poking the MSR to enable APIC assist on that CPU, since enabling APIC assist
> is clearly going to modify the way in which interrupts are handled. If that's
> not the case though then I guess that is probably the cause of the issue; I
> never really considered protecting interrupt handling against APIC assist
> being enabled on the same CPU.
>
I think I've spotted it...
If the guest is indeed setting up APIC assist but not actually using it then I think we get into this situation...
- On return to guest vlapic_has_pending_irq() finds a bit set in the IRR, then vlapic_ack_pending_irq() calls viridian_start_apic_assist() which latches the vector, sets the bit in the ISR and clears it from the IRR.
- The guest then processes the interrupt but EOIs it normally, therefore clearing the bit in the ISR.
- On next return to guest vlapic_has_pending_irq() calls viridian_complete_apic_assist(), which discovers the assist bit still set in the page and therefore leaves the latched vector in place, but finds another bit set in the IRR.
- vlapic_ack_pending_irq() is then called, the ISR is clear, so another call is made to viridian_start_apic_assist() and this then calls domain_crash() because it finds the previously latched vector.
I think the correct solution to this is to call viridian_abort_apic_assist() in vlapic_EOI_set() when the vector is cleared from the ISR.
Paul
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prev parent reply other threads:[~2018-01-17 10:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-16 8:43 [xen-unstable test] 118078: regressions - FAIL osstest service owner
2018-01-16 8:57 ` Jan Beulich
2018-01-16 9:26 ` Paul Durrant
2018-01-16 17:30 ` Paul Durrant
2018-01-17 8:51 ` Jan Beulich
2018-01-17 9:37 ` Paul Durrant
2018-01-17 10:17 ` Paul Durrant [this message]
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