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>

1 files changed, 5 insertions, 0 deletions

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e2edb1103002..e2c1fb8d35ce 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -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;