Re: Commit "x86/kvm: Move context tracking where it belongs" broke guest time accounting

[Thomas Gleixner]

On Fri, Apr 09 2021 at 16:13, Wanpeng Li wrote:
> On Thu, 8 Apr 2021 at 21:19, Thomas Gleixner <tglx@linutronix.de> wrote:
>
> +    account_guest_enter();

This wants to move into the instrumentation_begin/end() section above.

>      guest_enter_irqoff();
>      lockdep_hardirqs_on(CALLER_ADDR0);
>
> @@ -3759,6 +3760,8 @@ static noinstr void svm_vcpu_enter_exit(struct
> kvm_vcpu *vcpu)
>       */
>      lockdep_hardirqs_off(CALLER_ADDR0);
>      guest_exit_irqoff();
> +    if (vtime_accounting_enabled_this_cpu())
> +        account_guest_exit();

This time below. Aside of that I'd suggest to have two inlines instead
of having the conditional here.

>
>  #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
> -/* must be called with irqs disabled */
> -static __always_inline void guest_enter_irqoff(void)
> +static __always_inline void account_guest_enter(void)
>  {
>      instrumentation_begin();
>      if (vtime_accounting_enabled_this_cpu())
> @@ -113,7 +112,11 @@ static __always_inline void guest_enter_irqoff(void)
>      else
>          current->flags |= PF_VCPU;
>      instrumentation_end();

If you move the invocation into the instrumentable section then this
instrumentation_begin/end() can be removed.

Something like the below +/- the obligatory bikeshed painting
vs. function names.

Thanks,

        tglx
---
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3782,6 +3782,7 @@ static noinstr void svm_vcpu_enter_exit(
         * accordingly.
         */
        instrumentation_begin();
+       vtime_account_guest_enter();
        trace_hardirqs_on_prepare();
        lockdep_hardirqs_on_prepare(CALLER_ADDR0);
        instrumentation_end();
@@ -3816,6 +3817,7 @@ static noinstr void svm_vcpu_enter_exit(
 
        instrumentation_begin();
        trace_hardirqs_off_finish();
+       vtime_account_guest_exit();
        instrumentation_end();
 }
 
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6655,6 +6655,7 @@ static noinstr void vmx_vcpu_enter_exit(
         * accordingly.
         */
        instrumentation_begin();
+       vtime_account_guest_enter();
        trace_hardirqs_on_prepare();
        lockdep_hardirqs_on_prepare(CALLER_ADDR0);
        instrumentation_end();
@@ -6693,6 +6694,7 @@ static noinstr void vmx_vcpu_enter_exit(
 
        instrumentation_begin();
        trace_hardirqs_off_finish();
+       vtime_account_guest_exit();
        instrumentation_end();
 }
 
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9200,6 +9200,7 @@ static int vcpu_enter_guest(struct kvm_v
        ++vcpu->stat.exits;
        local_irq_disable();
        kvm_after_interrupt(vcpu);
+       vcpu_account_guest_exit();
 
        if (lapic_in_kernel(vcpu)) {
                s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -107,13 +107,6 @@ static inline void context_tracking_init
 /* must be called with irqs disabled */
 static __always_inline void guest_enter_irqoff(void)
 {
-       instrumentation_begin();
-       if (vtime_accounting_enabled_this_cpu())
-               vtime_guest_enter(current);
-       else
-               current->flags |= PF_VCPU;
-       instrumentation_end();
-
        if (context_tracking_enabled())
                __context_tracking_enter(CONTEXT_GUEST);
 
@@ -135,37 +128,18 @@ static __always_inline void guest_exit_i
 {
        if (context_tracking_enabled())
                __context_tracking_exit(CONTEXT_GUEST);
-
-       instrumentation_begin();
-       if (vtime_accounting_enabled_this_cpu())
-               vtime_guest_exit(current);
-       else
-               current->flags &= ~PF_VCPU;
-       instrumentation_end();
 }
 
 #else
 static __always_inline void guest_enter_irqoff(void)
 {
-       /*
-        * This is running in ioctl context so its safe
-        * to assume that it's the stime pending cputime
-        * to flush.
-        */
        instrumentation_begin();
-       vtime_account_kernel(current);
-       current->flags |= PF_VCPU;
        rcu_virt_note_context_switch(smp_processor_id());
        instrumentation_end();
 }
 
 static __always_inline void guest_exit_irqoff(void)
 {
-       instrumentation_begin();
-       /* Flush the guest cputime we spent on the guest */
-       vtime_account_kernel(current);
-       current->flags &= ~PF_VCPU;
-       instrumentation_end();
 }
 #endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
 
@@ -178,4 +152,24 @@ static inline void guest_exit(void)
        local_irq_restore(flags);
 }
 
+static __always_inline void vtime_account_guest_enter(void)
+{
+       if (vtime_accounting_enabled_this_cpu())
+               vtime_guest_enter(current);
+       else
+               current->flags |= PF_VCPU;
+}
+
+static __always_inline void vtime_account_guest_exit(void)
+{
+       if (vtime_accounting_enabled_this_cpu())
+               vtime_guest_exit(current);
+}
+
+static __always_inline void vcpu_account_guest_exit(void)
+{
+       if (!vtime_accounting_enabled_this_cpu())
+               current->flags &= ~PF_VCPU;
+}
+
 #endif