From: Wanpeng Li <wanpengli@xxxxxxxxxxx> commit 160457140187c5fb127b844e5a85f87f00a01b14 upstream. 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 the main sequence of vcpu_enter_guest(), including the call into vendor code to actually enter and exit the guest. 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") Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/20210505002735.1684165-4-seanjc@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kvm/svm/svm.c | 6 +++--- arch/x86/kvm/vmx/vmx.c | 6 +++--- arch/x86/kvm/x86.c | 9 +++++++++ 3 files changed, 15 insertions(+), 6 deletions(-) --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3532,15 +3532,15 @@ static noinstr void svm_vcpu_enter_exit( * have them in state 'on' as recorded before entering guest mode. * Same as enter_from_user_mode(). * - * guest_exit_irqoff() restores host context and reinstates RCU if - * enabled and required. + * context_tracking_guest_exit() restores host context and reinstates + * RCU if enabled and required. * * This needs to be done before the below as native_read_msr() * contains a tracepoint and x86_spec_ctrl_restore_host() calls * into world and some more. */ lockdep_hardirqs_off(CALLER_ADDR0); - guest_exit_irqoff(); + context_tracking_guest_exit(); instrumentation_begin(); trace_hardirqs_off_finish(); --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6640,15 +6640,15 @@ static noinstr void vmx_vcpu_enter_exit( * have them in state 'on' as recorded before entering guest mode. * Same as enter_from_user_mode(). * - * guest_exit_irqoff() restores host context and reinstates RCU if - * enabled and required. + * context_tracking_guest_exit() restores host context and reinstates + * RCU if enabled and required. * * This needs to be done before the below as native_read_msr() * contains a tracepoint and x86_spec_ctrl_restore_host() calls * into world and some more. */ lockdep_hardirqs_off(CALLER_ADDR0); - guest_exit_irqoff(); + context_tracking_guest_exit(); instrumentation_begin(); trace_hardirqs_off_finish(); --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9063,6 +9063,15 @@ static int vcpu_enter_guest(struct kvm_v local_irq_disable(); kvm_after_interrupt(vcpu); + /* + * 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. Waiting until IRQs are enabled degrades the accuracy + * of accounting via context tracking, but the loss of accuracy is + * acceptable for all known use cases. + */ + vtime_account_guest_exit(); + if (lapic_in_kernel(vcpu)) { s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta; if (delta != S64_MIN) {
