linux-kernel - [PATCH v3 3/9] KVM: x86: Defer tick-based accounting 'til after IRQ handling

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Date:   Thu, 15 Apr 2021 15:21:00 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Michael Tokarev <mjt@....msk.ru>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCH v3 3/9] KVM: x86: Defer tick-based accounting 'til after IRQ handling

From: Wanpeng Li <wanpengli@...cent.com>

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@...utronix.de>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Michael Tokarev <mjt@....msk.ru>
Cc: stable@...r.kernel.org#v5.9-rc1+
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
Co-developed-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 13 ++++++++++---
 arch/x86/kvm/vmx/vmx.c | 13 ++++++++++---
 arch/x86/kvm/x86.c     |  8 ++++++++
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 48b396f33bee..bb2aa0dde7c5 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3750,17 +3750,24 @@ 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_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();
 
 	instrumentation_begin();
+	/*
+	 * Account guest time when precise accounting based on context tracking
+	 * is enabled.  Tick based accounting is deferred until after IRQs that
+	 * occurred within the VM-Enter/VM-Exit "window" are handled.
+	 */
+	if (vtime_accounting_enabled_this_cpu())
+		vtime_account_guest_exit();
 	trace_hardirqs_off_finish();
 	instrumentation_end();
 }
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c05e6e2854b5..5ae9dc197048 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6639,17 +6639,24 @@ 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_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();
 
 	instrumentation_begin();
+	/*
+	 * Account guest time when precise accounting based on context tracking
+	 * is enabled.  Tick based accounting is deferred until after IRQs that
+	 * occurred within the VM-Enter/VM-Exit "window" are handled.
+	 */
+	if (vtime_accounting_enabled_this_cpu())
+		vtime_account_guest_exit();
 	trace_hardirqs_off_finish();
 	instrumentation_end();
 }
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();
+
 	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