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

Maxim Levitsky
2021-08-10T21:21:41Z

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.
>
> Best regards,
> Maxim Levitsky
>
> Maxim Levitsky (14):
> KVM: x86/mmu: fix parameters to kvm_flush_remote_tlbs_with_address
> KVM: x86/mmu: add comment explaining arguments to kvm_zap_gfn_range
> KVM: x86/mmu: bump mmu notifier count in kvm_zap_gfn_range
> KVM: x86/mmu: rename try_async_pf to kvm_faultin_pfn
> KVM: x86/mmu: allow kvm_faultin_pfn to return page fault handling code
> KVM: x86/mmu: allow APICv memslot to be enabled but invisible
> KVM: x86: don't disable APICv memslot when inhibited
> KVM: x86: APICv: fix race in kvm_request_apicv_update on SVM
> KVM: SVM: add warning for mistmatch between AVIC vcpu state and AVIC
> inhibition
> KVM: SVM: remove svm_toggle_avic_for_irq_window
> KVM: SVM: avoid refreshing avic if its state didn't change
> KVM: SVM: move check for kvm_vcpu_apicv_active outside of
> avic_vcpu_{put|load}
> KVM: SVM: call avic_vcpu_load/avic_vcpu_put when enabling/disabling
> AVIC
> KVM: SVM: AVIC: drop unsupported AVIC base relocation code
>
> Sean Christopherson (1):
> Revert "KVM: x86/mmu: Allow zap gfn range to operate under the mmu
> read lock"
>
> Vitaly Kuznetsov (1):
> KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in
> use
>
> arch/x86/include/asm/kvm-x86-ops.h | 1 -
> arch/x86/include/asm/kvm_host.h | 13 +++++-
> arch/x86/kvm/hyperv.c | 32 ++++++++++---
> arch/x86/kvm/mmu/mmu.c | 75 ++++++++++++++++++++----------
> arch/x86/kvm/mmu/paging_tmpl.h | 6 +--
> arch/x86/kvm/mmu/tdp_mmu.c | 15 ++----
> arch/x86/kvm/mmu/tdp_mmu.h | 11 ++---
> arch/x86/kvm/svm/avic.c | 49 +++++++------------
> arch/x86/kvm/svm/svm.c | 21 ++++-----
> arch/x86/kvm/svm/svm.h | 8 ----
> arch/x86/kvm/x86.c | 67 +++++++++++++++-----------
> include/linux/kvm_host.h | 5 ++
> virt/kvm/kvm_main.c | 7 ++-
> 13 files changed, 174 insertions(+), 136 deletions(-)
>
> --
> 2.26.3
>
>