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KVM: x86: Disable APIC logical map if logical ID covers multiple MDAs

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Disable the optimized APIC logical map if a logical ID covers multiple
MDAs, i.e. if a vCPU has multiple bits set in its ID.  In logical mode,
events match if "ID & MDA != 0", i.e. creating an entry for only the
first bit can cause interrupts to be missed.

Note, creating an entry for every bit is also wrong as KVM would generate
IPIs for every matching bit.  It would be possible to teach KVM to play
nice with this edge case, but it is very much an edge case and probably
not used in any real world OS, i.e. it's not worth optimizing.

Fixes: 1e08ec4a130e ("KVM: optimize apic interrupt delivery")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20230106011306.85230-21-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-01-06 01:12:53 +00:00 committed by Paolo Bonzini
parent 76e527509d
commit 2bf934aadc
1 changed files with 8 additions and 2 deletions
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10
arch/x86/kvm/lapic.c
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@ -343,8 +343,14 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
continue;
}
if (mask)
cluster[ffs(mask) - 1] = apic;
if (!mask)
continue;
if (!is_power_of_2(mask)) {
new->logical_mode = KVM_APIC_MODE_MAP_DISABLED;
continue;
}
cluster[ffs(mask) - 1] = apic;
}
out:
old = rcu_dereference_protected(kvm->arch.apic_map,