From: Wanpeng Li <wanpen...@tencent.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 <t...@linutronix.de>
Cc: Sean Christopherson <sea...@google.com>
Cc: Michael Tokarev <m...@tls.msk.ru>
Cc: sta...@vger.kernel.org#v5.9-rc1+
Suggested-by: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Wanpeng Li <wanpen...@tencent.com>
Co-developed-by: Sean Christopherson <sea...@google.com>
Signed-off-by: Sean Christopherson <sea...@google.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

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