Re: [PATCH v4 00/16] My AVIC patch queue

Paolo Bonzini
2021-08-11T08:08:54Z

On 10/08/21 23:21, Maxim Levitsky wrote:
> On Tue, 2021-08-10 at 23:52 +0300, Maxim Levitsky wrote:
>> Hi!
>>
>> This is a series of bugfixes to the AVIC dynamic inhibition, which was
>> made while trying to fix bugs as much as possible in this area and trying
>> to make the AVIC+SYNIC conditional enablement work.
>>
>> * Patches 1,3-8 are code from Sean Christopherson which
>
> I mean patches 1,4-8. I forgot about patch 3 which I also added,
> which just added a comment about parameters of the kvm_flush_remote_tlbs_with_address.
>
> Best regards,
> Maxim Levitsky
>
>> implement an alternative approach of inhibiting AVIC without
>> disabling its memslot.
>>
>> V4: addressed review feedback.
>>
>> * Patch 2 is new and it fixes a bug in kvm_flush_remote_tlbs_with_address
>>
>> * Patches 9-10 in this series fix a race condition which can cause
>> a lost write from a guest to APIC when the APIC write races
>> the AVIC un-inhibition, and add a warning to catch this problem
>> if it re-emerges again.
>>
>> V4: applied review feedback from Paolo
>>
>> * Patch 11 is the patch from Vitaly about allowing AVIC with SYNC
>> as long as the guest doesn’t use the AutoEOI feature. I only slightly
>> changed it to expose the AutoEOI cpuid bit regardless of AVIC enablement.
>>
>> V4: fixed a race that Paolo pointed out.
>>
>> * Patch 12 is a refactoring that is now possible in SVM AVIC inhibition code,
>> because the RCU lock is not dropped anymore.
>>
>> * Patch 13-15 fixes another issue I found in AVIC inhibit code:
>>
>> Currently avic_vcpu_load/avic_vcpu_put are called on userspace entry/exit
>> from KVM (aka kvm_vcpu_get/kvm_vcpu_put), and these functions update the
>> "is running" bit in the AVIC physical ID remap table and update the
>> target vCPU in iommu code.
>>
>> However both of these functions don't do anything when AVIC is inhibited
>> thus the "is running" bit will be kept enabled during the exit to userspace.
>> This shouldn't be a big issue as the caller
>> doesn't use the AVIC when inhibited but still inconsistent and can trigger
>> a warning about this in avic_vcpu_load.
>>
>> To be on the safe side I think it makes sense to call
>> avic_vcpu_put/avic_vcpu_load when inhibiting/uninhibiting the AVIC.
>> This will ensure that the work these functions do is matched.
>>
>> V4: I splitted a single patch to 3 patches to make it easier
>> to review, and applied Paolo's review feedback.
>>
>> * Patch 16 removes the pointless APIC base
>> relocation from AVIC to make it consistent with the rest of KVM.
>>
>> (both AVIC and APICv only support default base, while regular KVM,
>> sort of support any APIC base as long as it is not RAM.
>> If guest attempts to relocate APIC base to non RAM area,
>> while APICv/AVIC are active, the new base will be non accelerated,
>> while the default base will continue to be AVIC/APICv backed).
>>
>> On top of that if guest uses different APIC bases on different vCPUs,
>> KVM doesn't honour the fact that the MMIO range should only be active
>> on that vCPU.

No problem, b4 diff is my friend. :) Queued, thanks.

Paolo