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

[Paolo Bonzini]

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