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

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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: 87fa7f3e98 ("x86/kvm: Move context tracking where it belongs")
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210505002735.1684165-4-seanjc@google.com
This commit is contained in:
Wanpeng Li 2021-05-04 17:27:30 -07:00 committed by Thomas Gleixner
parent 88d8220bbf
commit 1604571401
3 changed files with 15 additions and 6 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

6
arch/x86/kvm/svm/svm.c
View file

@ -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();

6
arch/x86/kvm/vmx/vmx.c
View file

@ -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();

9
arch/x86/kvm/x86.c
View file

@ -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) {