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). When using tick-based accounting, time is
accounted to the guest when PF_VCPU is set when the tick IRQ handler
runs. The current approach of unconditionally accounting time in
kvm_guest_exit_irqoff() prevents IRQs that occur in the guest from ever
being processed with PF_VCPU set, since PF_VCPU ends up being set only
during the relatively short VM-Enter sequence, which runs entirely with
IRQs disabled.
Fixes: 87fa7f3e98a131 ("x86/kvm: Move context tracking where it belongs")
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Michael Tokarev <mjt@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 8 ++++++++
arch/x86/kvm/x86.h | 9 ++++++---
2 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 16fb39503296..096bbf50b7a9 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 account, 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 (!IS_ENABLED(CONFIG_VIRT_CPU_ACCOUNTING_GEN))
+ kvm_vtime_account_guest_exit();
+
if (lapic_in_kernel(vcpu)) {
s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
if (delta != S64_MIN) {
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 74ef92f47db8..039a7d585925 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -38,15 +38,18 @@ static __always_inline void kvm_guest_exit_irqoff(void)
* 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_irqoff() 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_irqoff();
+
+ if (IS_ENABLED(CONFIG_VIRT_CPU_ACCOUNTING_GEN))
+ kvm_vtime_account_guest_exit();
instrumentation_begin();
trace_hardirqs_off_finish();
--
2.31.1.295.g9ea45b61b8-goog
