From: Sean Christopherson Date: Fri, 6 Jan 2023 01:12:53 +0000 (+0000) Subject: KVM: x86: Disable APIC logical map if logical ID covers multiple MDAs X-Git-Tag: v6.3-rc1~85^2~14^2~13 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=2bf934aadcac310810cc4fa120d1b576cae7e9da;p=thirdparty%2Flinux.git KVM: x86: Disable APIC logical map if logical ID covers multiple MDAs 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 Reviewed-by: Maxim Levitsky Message-Id: <20230106011306.85230-21-seanjc@google.com> Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index fd7726ff95c63..dca87bb6dd1ae 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -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,