From: Paolo Bonzini <pbonzini@redhat.com>
To: "Zhang, Yang Z" <yang.z.zhang@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH] KVM: x86: always exit on EOIs for interrupts listed in the IOAPIC redir table
Date: Wed, 06 Aug 2014 16:08:38 +0200 [thread overview]
Message-ID: <53E236E6.6050206@redhat.com> (raw)
In-Reply-To: <A9667DDFB95DB7438FA9D7D576C3D87E0AB51BA1@SHSMSX104.ccr.corp.intel.com>
Il 06/08/2014 16:03, Zhang, Yang Z ha scritto:
> Paolo Bonzini wrote on 2014-07-31:
>> Probably, the guest is masking the interrupt in the redirection table in
>> the interrupt routine, i.e. while the interrupt is set in a LAPIC's ISR.
>> The simplest fix is to ignore the masking state, we would rather have
>> an unnecessary exit rather than a missed IRQ ACK and anyway IOAPIC
>> interrupts are not as performance-sensitive as for example MSIs.
>
> I feel this fixing may hurt performance in some cases. If the mask
> bit is set, this means the vector in this entry may be used by other
> devices(like a assigned device). But here you set it in eoi exit bitmap
> and this will cause vmexit on each EOI which should not happen.
Note that this *was* reported on an assigned device.
IOAPIC should not be a performance-sensitive path. High-performance
assigned devices should be using MSIs.
Paolo
next prev parent reply other threads:[~2014-08-06 14:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-30 16:12 [PATCH] KVM: x86: always exit on EOIs for interrupts listed in the IOAPIC redir table Paolo Bonzini
2014-07-30 16:51 ` Alex Williamson
2014-08-06 14:03 ` Zhang, Yang Z
2014-08-06 14:08 ` Paolo Bonzini [this message]
2014-08-07 1:31 ` Zhang, Yang Z
2014-08-07 6:13 ` Paolo Bonzini
2014-08-07 6:17 ` Zhang, Yang Z
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