+tglx
On Tue, Jan 05, 2021, Nitesh Narayan Lal wrote:
> This reverts commit d7a08882a0a4b4e176691331ee3f492996579534.
>
> After the introduction of the patch:
>
> 87fa7f3e9: x86/kvm: Move context tracking where it belongs
>
> since we have moved guest_exit_irqoff closer to the VM-Exit, explicit
> enabling of irqs to process pending interrupts should not be required
> within vcpu_enter_guest anymore.
Ugh, except that commit completely broke tick-based accounting, on both Intel
and AMD. With guest_exit_irqoff() being called immediately after VM-Exit, any
tick that happens after IRQs are disabled will be accounted to the host. E.g.
on Intel, even an IRQ VM-Exit that has already been acked by the CPU isn't
processed until kvm_x86_ops.handle_exit_irqoff(), well after PF_VCPU has been
cleared.
CONFIG_VIRT_CPU_ACCOUNTING_GEN=y should still work (I didn't bother to verify).
Thomas, any clever ideas? Handling IRQs in {vmx,svm}_vcpu_enter_exit() isn't an
option as KVM hasn't restored enough state to handle an IRQ, e.g. PKRU and XCR0
are still guest values. Is it too heinous to fudge PF_VCPU across KVM's
"pending" IRQ handling? E.g. this god-awful hack fixes the accounting:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 836912b42030..5a777fd35b4b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9028,6 +9028,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
vcpu->mode = OUTSIDE_GUEST_MODE;
smp_wmb();
+ current->flags |= PF_VCPU;
kvm_x86_ops.handle_exit_irqoff(vcpu);
/*
@@ -9042,6 +9043,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
++vcpu->stat.exits;
local_irq_disable();
kvm_after_interrupt(vcpu);
+ current->flags &= ~PF_VCPU;
if (lapic_in_kernel(vcpu)) {
s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
> Conflicts:
> arch/x86/kvm/svm.c
>
> Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
> ---
> arch/x86/kvm/svm/svm.c | 9 +++++++++
> arch/x86/kvm/x86.c | 11 -----------
> 2 files changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index cce0143a6f80..c9b2fbb32484 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4187,6 +4187,15 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
>
> static void svm_handle_exit_irqoff(struct kvm_vcpu *vcpu)
> {
> + kvm_before_interrupt(vcpu);
> + local_irq_enable();
> + /*
> + * We must have an instruction with interrupts enabled, so
> + * the timer interrupt isn't delayed by the interrupt shadow.
> + */
> + asm("nop");
> + local_irq_disable();
> + kvm_after_interrupt(vcpu);
> }
>
> static void svm_sched_in(struct kvm_vcpu *vcpu, int cpu)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 3f7c1fc7a3ce..3e17c9ffcad8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9023,18 +9023,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>
> kvm_x86_ops.handle_exit_irqoff(vcpu);
>
> - /*
> - * Consume any pending interrupts, including the possible source of
> - * VM-Exit on SVM and any ticks that occur between VM-Exit and now.
> - * An instruction is required after local_irq_enable() to fully unblock
> - * interrupts on processors that implement an interrupt shadow, the
> - * stat.exits increment will do nicely.
> - */
> - kvm_before_interrupt(vcpu);
> - local_irq_enable();
> ++vcpu->stat.exits;
> - local_irq_disable();
> - kvm_after_interrupt(vcpu);
>
> if (lapic_in_kernel(vcpu)) {
> s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta;
> --
> 2.27.0
>
