| Message ID | 20210206004218.312023-1-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC] KVM: x86: Set PF_VCPU when processing IRQs to fix tick-based accounting | expand |
Sean Christopherson <seanjc@google.com> writes: > Temporarily set PF_VCPU while processing IRQ VM-Exits so that a tick IRQ > accounts the time slice to the guest. Tick-based accounting of guest > time is currently broken as PF_VCPU is only set during the relatively > short VM-Enter sequence, which runs entirely with IRQs disabled, and IRQs > that occur in the guest are processed well after PF_VCPU is cleared. > > Keep PF_VCPU set across both VMX's processing of already-acked IRQs > (handle_exit_irqoff()) and the explicit IRQ window (SVM's processing, > plus ticks that occur immediately after VM-Exit on both VMX and SVM). > > Fixes: 87fa7f3e98a1 ("x86/kvm: Move context tracking where it belongs") > Cc: stable@vger.kernel.org > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > > This is quite obnoxious, hence the RFC, but I can't think of a clever, > less ugly way to fix the accounting. > > arch/x86/kvm/x86.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index d9f931c63293..6ddf341cd755 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -9118,6 +9118,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > vcpu->mode = OUTSIDE_GUEST_MODE; > smp_wmb(); > > + /* > + * Temporarily pretend this task is running a vCPU when potentially > + * processing an IRQ exit, including the below opening of an IRQ > + * window. Tick-based accounting of guest time relies on PF_VCPU > + * being set when the tick IRQ handler runs. > + */ > + current->flags |= PF_VCPU; Should we do it only when !vtime_accounting_enabled_cpu() maybe? > static_call(kvm_x86_handle_exit_irqoff)(vcpu); > > /* > @@ -9132,6 +9139,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > ++vcpu->stat.exits; > local_irq_disable(); > kvm_after_interrupt(vcpu); > + current->flags &= ~PF_VCPU; > > if (lapic_in_kernel(vcpu)) { > s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index d9f931c63293..6ddf341cd755 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9118,6 +9118,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) vcpu->mode = OUTSIDE_GUEST_MODE; smp_wmb(); + /* + * Temporarily pretend this task is running a vCPU when potentially + * processing an IRQ exit, including the below opening of an IRQ + * window. Tick-based accounting of guest time relies on PF_VCPU + * being set when the tick IRQ handler runs. + */ + current->flags |= PF_VCPU; static_call(kvm_x86_handle_exit_irqoff)(vcpu); /* @@ -9132,6 +9139,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) ++vcpu->stat.exits; local_irq_disable(); kvm_after_interrupt(vcpu); + current->flags &= ~PF_VCPU; if (lapic_in_kernel(vcpu)) { s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
Temporarily set PF_VCPU while processing IRQ VM-Exits so that a tick IRQ accounts the time slice to the guest. Tick-based accounting of guest time is currently broken as PF_VCPU is only set during the relatively short VM-Enter sequence, which runs entirely with IRQs disabled, and IRQs that occur in the guest are processed well after PF_VCPU is cleared. Keep PF_VCPU set across both VMX's processing of already-acked IRQs (handle_exit_irqoff()) and the explicit IRQ window (SVM's processing, plus ticks that occur immediately after VM-Exit on both VMX and SVM). Fixes: 87fa7f3e98a1 ("x86/kvm: Move context tracking where it belongs") Cc: stable@vger.kernel.org Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sean Christopherson <seanjc@google.com> --- This is quite obnoxious, hence the RFC, but I can't think of a clever, less ugly way to fix the accounting. arch/x86/kvm/x86.c | 8 ++++++++ 1 file changed, 8 insertions(+)