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KVM: LAPIC: cap __delay at lapic_timer_advance_ns

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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>
This commit is contained in:
Marcelo Tosatti 2016-06-20 22:33:48 -03:00 committed by Paolo Bonzini
parent 8d93c874ac
commit b606f189c7
1 changed files with 2 additions and 1 deletions
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3
arch/x86/kvm/lapic.c
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@ -1310,7 +1310,8 @@ 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)