On Thu, Apr 15, 2021 at 03:21:00PM -0700, Sean Christopherson wrote:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> When using tick-based accounting, defer the call to account guest time
> until after servicing any IRQ(s) that happened in the guest or
> immediately after VM-Exit. Tick-based accounting of vCPU time relies on
> PF_VCPU being set when the tick IRQ handler runs, and IRQs are blocked
> throughout {svm,vmx}_vcpu_enter_exit().
>
> This fixes a bug[*] where reported guest time remains '0', even when
> running an infinite loop in the guest.
>
> [*] https://bugzilla.kernel.org/show_bug.cgi?id=209831
>
> Fixes: 87fa7f3e98a131 ("x86/kvm: Move context tracking where it belongs")
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Cc: Michael Tokarev <mjt@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx#v5.9-rc1+
> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 16fb39503296..e4d475df1d4a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9230,6 +9230,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> local_irq_disable();
> kvm_after_interrupt(vcpu);
>
> + /*
> + * When using tick-based accounting, wait until after servicing IRQs to
> + * account guest time so that any ticks that occurred while running the
> + * guest are properly accounted to the guest.
> + */
> + if (!vtime_accounting_enabled_this_cpu())
> + vtime_account_guest_exit();
Can we rather have instead:
static inline void tick_account_guest_exit(void)
{
if (!vtime_accounting_enabled_this_cpu())
current->flags &= ~PF_VCPU;
}
It duplicates a bit of code but I think this will read less confusing.
Thanks.
> +
> if (lapic_in_kernel(vcpu)) {
> s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
> if (delta != S64_MIN) {
> --
> 2.31.1.368.gbe11c130af-goog
>
