diff options
| author | Sean Christopherson <sean.j.christopherson@intel.com> | 2019-07-10 09:07:34 -0700 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2019-07-11 15:10:22 +0200 |
| commit | d7a08882a0a4b4e176691331ee3f492996579534 (patch) | |
| tree | ecfa90d990e01fd7e80d5eaa3093348fcd27f7b0 /arch/x86 | |
| parent | 66bb8a065f5aedd4551d8d3fbce582972f65c2e1 (diff) | |
KVM: x86: Unconditionally enable irqs in guest context
On VMX, KVM currently does not re-enable irqs until after it has exited
the guest context. As a result, a tick that fires in the window between
VM-Exit and guest_exit_irqoff() will be accounted as system time. While
said window is relatively small, it's large enough to be problematic in
some configurations, e.g. if VM-Exits are consistently occurring a hair
earlier than the tick irq.
Intentionally toggle irqs back off so that guest_exit_irqoff() can be
used in lieu of guest_exit() in order to avoid the save/restore of flags
in guest_exit(). On my Haswell system, "nop; cli; sti" is ~6 cycles,
versus ~28 cycles for "pushf; pop <reg>; cli; push <reg>; popf".
Fixes: f2485b3e0c6c0 ("KVM: x86: use guest_exit_irqoff")
Reported-by: Wei Yang <w90p710@gmail.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/kvm/svm.c | 10 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 11 |
2 files changed, 12 insertions, 9 deletions
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 5270711e787f..98b848fcf3e3 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -6184,15 +6184,7 @@ out: 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 81faceba8cec..0347b1e41c40 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8046,7 +8046,18 @@ 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); guest_exit_irqoff(); if (lapic_in_kernel(vcpu)) { |