Commit 16045714 authored by Wanpeng Li's avatar Wanpeng Li Committed by Thomas Gleixner
Browse files

KVM: x86: Defer vtime accounting 'til after IRQ handling 

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: 87fa7f3e ("x86/kvm: Move context tracking where it belongs")
Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Co-developed-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarWanpeng Li <wanpengli@tencent.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210505002735.1684165-4-seanjc@google.com
parent 88d8220b

arch/x86/kvm/svm/svm.c

+3 −3
Original line number Diff line number Diff line
@@ -3753,15 +3753,15 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu) 
	 * 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();

arch/x86/kvm/vmx/vmx.c

+3 −3
Original line number Diff line number Diff line
@@ -6703,15 +6703,15 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu, 
	 * 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();

arch/x86/kvm/x86.c

+9 −0
Original line number Diff line number Diff line
@@ -9315,6 +9315,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) 
	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) {