Re: [PATCH v2 0/4] KVM: x86: APICv cleanups

Paolo Bonzini
2021-10-22T10:12:42Z

On 22/10/21 02:49, Sean Christopherson wrote:
> APICv cleanups and a dissertation on handling concurrent APIC access page
> faults and APICv inhibit updates.
>
> I've tested this but haven't hammered the AVIC stuff, I'd appreciate it if
> someone with the Hyper-V setup can beat on the AVIC toggling.
>
> Sean Christopherson (4):
> KVM: x86/mmu: Use vCPU's APICv status when handling APIC_ACCESS
> memslot
> KVM: x86: Move SVM's APICv sanity check to common x86
> KVM: x86: Move apicv_active flag from vCPU to in-kernel local APIC
> KVM: x86: Use rw_semaphore for APICv lock to allow vCPU parallelism
>
> arch/x86/include/asm/kvm_host.h | 3 +-
> arch/x86/kvm/hyperv.c | 4 +--
> arch/x86/kvm/lapic.c | 46 ++++++++++---------------
> arch/x86/kvm/lapic.h | 5 +--
> arch/x86/kvm/mmu/mmu.c | 29 ++++++++++++++--
> arch/x86/kvm/svm/avic.c | 2 +-
> arch/x86/kvm/svm/svm.c | 2 --
> arch/x86/kvm/vmx/vmx.c | 4 +--
> arch/x86/kvm/x86.c | 59 ++++++++++++++++++++++-----------
> 9 files changed, 93 insertions(+), 61 deletions(-)
>

Queued, thanks. I only made small edits to the comment in patch
1, to make it very slightly shorter.

* 2a. APICv is globally disabled but locally enabled, and this
* vCPU acquires mmu_lock before __kvm_request_apicv_update
* calls kvm_zap_gfn_range(). This vCPU will install a stale
* SPTE, but no one will consume it as (a) no vCPUs can be
* running due to the kick from KVM_REQ_APICV_UPDATE, and
* (b) because KVM_REQ_APICV_UPDATE is raised before the VM
* state is update, vCPUs attempting to service the request
* will block on apicv_update_lock. The update flow will
* then zap the SPTE and release the lock.

Paolo