diff mbox series

[5.10,276/290] KVM: x86: Ensure deadline timer has truly expired before posting its IRQ

Message ID 20210315135551.359947615@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman March 15, 2021, 1:56 p.m. UTC 
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

From: Sean Christopherson <seanjc@google.com>

commit beda430177f56656e7980dcce93456ffaa35676b upstream.

When posting a deadline timer interrupt, open code the checks guarding
__kvm_wait_lapic_expire() in order to skip the lapic_timer_int_injected()
check in kvm_wait_lapic_expire().  The injection check will always fail
since the interrupt has not yet be injected.  Moving the call after
injection would also be wrong as that wouldn't actually delay delivery
of the IRQ if it is indeed sent via posted interrupt.

Fixes: 010fd37fddf6 ("KVM: LAPIC: Reduce world switch latency caused by timer_advance_ns")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210305021808.3769732-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kvm/lapic.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)
diff mbox series

Patch

--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1641,7 +1641,16 @@  static void apic_timer_expired(struct kv
 	}
 
 	if (kvm_use_posted_timer_interrupt(apic->vcpu)) {
-		kvm_wait_lapic_expire(vcpu);
+		/*
+		 * Ensure the guest's timer has truly expired before posting an
+		 * interrupt.  Open code the relevant checks to avoid querying
+		 * lapic_timer_int_injected(), which will be false since the
+		 * interrupt isn't yet injected.  Waiting until after injecting
+		 * is not an option since that won't help a posted interrupt.
+		 */
+		if (vcpu->arch.apic->lapic_timer.expired_tscdeadline &&
+		    vcpu->arch.apic->lapic_timer.timer_advance_ns)
+			__kvm_wait_lapic_expire(vcpu);
 		kvm_apic_inject_pending_timer_irqs(apic);
 		return;
 	}