diff mbox series

[SRU,X,2/2] KVM: LAPIC: cap __delay at lapic_timer_advance_ns

Message ID 20190227191950.12074-3-gpiccoli@canonical.com
State New
Headers show
Series Hard lockups due to unrestricted lapic timer delay | expand

Commit Message

Guilherme G. Piccoli Feb. 27, 2019, 7:19 p.m. UTC 
From: Marcelo Tosatti <mtosatti@redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1817918

The host timer which emulates the guest LAPIC TSC deadline
timer has its expiration diminished by lapic_timer_advance_ns
nanoseconds. Therefore if, at wait_lapic_expire, a difference
larger than lapic_timer_advance_ns is encountered, delay at most
lapic_timer_advance_ns.

This fixes a problem where the guest can cause the host
to delay for large amounts of time.

Reported-by: Alan Jenkins <alan.christopher.jenkins@gmail.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit b606f189c7d5bf9b875bba168162fe05287880fe)
Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
---
 arch/x86/kvm/lapic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 76e8295517ed..e1edbf9c4033 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1265,7 +1265,8 @@  void wait_lapic_expire(struct kvm_vcpu *vcpu)
 
 	/* __delay is delay_tsc whenever the hardware has TSC, thus always.  */
 	if (guest_tsc < tsc_deadline)
-		__delay(tsc_deadline - guest_tsc);
+		__delay(min(tsc_deadline - guest_tsc,
+			nsec_to_cycles(vcpu, lapic_timer_advance_ns)));
 }
 
 static void start_apic_timer(struct kvm_lapic *apic)