KVM: x86: Disable APIC logical map if vCPUs are aliased in logical mode

Disable the optimized APIC logical map if multiple vCPUs are aliased to
the same logical ID.  Architecturally, all CPUs whose logical ID matches
the MDA are supposed to receive the interrupt; overwriting existing map
entries can result in missed IPIs.

Fixes: 1e08ec4a130e ("KVM: optimize apic interrupt delivery")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20230106011306.85230-22-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index dca87bb..9c0554b 100644 (file)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -346,11 +346,12 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
                if (!mask)
                        continue;
 
-               if (!is_power_of_2(mask)) {
+               ldr = ffs(mask) - 1;
+               if (!is_power_of_2(mask) || cluster[ldr]) {
                        new->logical_mode = KVM_APIC_MODE_MAP_DISABLED;
                        continue;
                }
-               cluster[ffs(mask) - 1] = apic;
+               cluster[ldr] = apic;
        }
 out:
        old = rcu_dereference_protected(kvm->arch.apic_map,