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Commit b606f189 authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Paolo Bonzini
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KVM: LAPIC: cap __delay at lapic_timer_advance_ns 



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: default avatarAlan Jenkins <alan.christopher.jenkins@gmail.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 8d93c874

arch/x86/kvm/lapic.c

+2 −1
Original line number Diff line number Diff line
@@ -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)