Commit 12806ba9 authored Nov 17, 2017 by Dr. David Alan Gilbert Committed by Paolo Bonzini Nov 27, 2017

KVM: lapic: Fixup LDR on load in x2apic

In x2apic mode the LDR is fixed based on the ID rather
than separately loadable like it was before x2.
When kvm_apic_set_state is called, the base is set, and if
it has the X2APIC_ENABLE flag set then the LDR is calculated;
however that value gets overwritten by the memcpy a few lines
below overwriting it with the value that came from userland.

The symptom is a lack of EOI after loading the state
(e.g. after a QEMU migration) and is due to the EOI bitmap
being wrong due to the incorrect LDR.  This was seen with
a Win2016 guest under Qemu with irqchip=split whose USB mouse
didn't work after a VM migration.

This corresponds to RH bug:
  https://bugzilla.redhat.com/show_bug.cgi?id=1502591



Reported-by: Yiqian Wei <yiwei@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: stable@vger.kernel.org
[Applied fixup from Liran Alon. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent e872fa94

arch/x86/kvm/lapic.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -2250,6 +2250,7 @@ static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
		{
		if (apic_x2apic_mode(vcpu->arch.apic)) {
		u32 id = (u32 )(s->regs + APIC_ID);
		u32 ldr = (u32 )(s->regs + APIC_LDR);

		if (vcpu->kvm->arch.x2apic_format) {
		if (*id != vcpu->vcpu_id)
		@@ -2260,6 +2261,10 @@ static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
		else
		*id <<= 24;
		}

		/* In x2APIC mode, the LDR is fixed and based on the id */
		if (set)
		ldr = kvm_apic_calc_x2apic_ldr(id);
		}

		return 0;

Admin message