| Message ID | 20210118230232.32247-2-matthew.ruffell@canonical.com |
|---|---|
| State | New |
| Headers | show |
| Series | kvm: Windows 2k19 with Hyper-v role gets stuck on pending hypervisor requests on cascadelake based kvm hosts | expand |
On 19.01.21 00:02, Matthew Ruffell wrote: > From: Sean Christopherson <sean.j.christopherson@intel.com> > > BugLink: https://bugs.launchpad.net/bugs/1911848 > > Re-request KVM_REQ_EVENT if vcpu_enter_guest() bails after processing > pending requests and an immediate exit was requested. This fixes a bug > where a pending event, e.g. VMX preemption timer, is delayed and/or lost > if the exit was deferred due to something other than a higher priority > _injected_ event, e.g. due to a pending nested VM-Enter. This bug only > affects the !injected case as kvm_x86_ops.cancel_injection() sets > KVM_REQ_EVENT to redo the injection, but that's purely serendipitous > behavior with respect to the deferred event. > > Note, emulated preemption timer isn't the only event that can be > affected, it simply happens to be the only event where not re-requesting > KVM_REQ_EVENT is blatantly visible to the guest. > > Fixes: f4124500c2c13 ("KVM: nVMX: Fully emulate preemption timer") > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > Message-Id: <20200423022550.15113-4-sean.j.christopherson@intel.com> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > (backported from commit 8081ad06b68a728e676d3b08e9ab70ce4039747b) > [mruffell: minor context adjustment] > Signed-off-by: Matthew Ruffell <matthew.ruffell@canonical.com> Acked-by: Stefan Bader <stefan.bader@canonical.com> > --- The regression potential is probably covering all bases but also sounding rather scary that way. I would say practically the change adds an exit case from immediate re-schedule (iiuc). So regression potential would be stuck guests with no cpu activity instead of 100% as before. Yeah, not sure that sounds better. But at least a little more specific. -Stefan > arch/x86/kvm/x86.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index e519e0af028a..dddbeb3ee2c6 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -8345,6 +8345,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > return r; > > cancel_injection: > + if (req_immediate_exit) > + kvm_make_request(KVM_REQ_EVENT, vcpu); > kvm_x86_ops->cancel_injection(vcpu); > if (unlikely(vcpu->arch.apic_attention)) > kvm_lapic_sync_from_vapic(vcpu); >
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index e519e0af028a..dddbeb3ee2c6 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8345,6 +8345,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) return r; cancel_injection: + if (req_immediate_exit) + kvm_make_request(KVM_REQ_EVENT, vcpu); kvm_x86_ops->cancel_injection(vcpu); if (unlikely(vcpu->arch.apic_attention)) kvm_lapic_sync_from_vapic(vcpu);