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Re: [Qemu-devel] [PATCH v11 00/28] IOMMU: Enable interrupt remapping for


From: Radim Krčmář
Subject: Re: [Qemu-devel] [PATCH v11 00/28] IOMMU: Enable interrupt remapping for Intel IOMMU
Date: Fri, 8 Jul 2016 20:06:12 +0200

2016-07-08 18:36+0200, Paolo Bonzini:
> On 08/07/2016 18:01, Radim Krčmář wrote:
>> The patchset doesn't work with if you have 16 APICs with IDs 0-15 and
>> then some more, because KVM has hacked x2APIC support that translates
>> logical interrupt with destination 0xff (first cluster of 16 VCPUs) into
>> a broadcast (also works with lowest-priority) and then picks VCPU > 16
>> as the destination, leading to messages like
>> 
>>   do_IRQ: 17.209 No irq handler for vector
>> 
>> The fun part is that this is how KVM wanted to behave, when it allowed
>> x2apic with unremapped ioapic. :(
>> KVM could either finally remove x2apic without IR or add a way in which
>> userspace could say whether an interrupt is x2APIC or not.
>> 
>> QEMU cannot do anything to work around the bug, so I think it would be
>> best to disable EIM for now.
> 
> What's the state of QEMU support for KVM_CAP_X2APIC_API?  If it can make
> it for hard freeze, it's not a showstopper for Peter's patch.

It works and is of postable quality, but the series bases on outdated
Igor's ACPI patches.  Rebasing KVM_CAP_X2APIC_API on top of IOMMU would
not complicate the situation too much and has good chances of getting in
before the hard freeze.  I'll coordinate with Igor on Monday.



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