diff mbox series

[v4,21/32] KVM: x86: Disable APIC logical map if logical ID covers multiple MDAs

Message ID 20221001005915.2041642-22-seanjc@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86: AVIC and local APIC fixes+cleanups | expand

Commit Message

Sean Christopherson Oct. 1, 2022, 12:59 a.m. UTC 
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>
---
 arch/x86/kvm/lapic.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index fca8bbb44375..7fd55e24247c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -338,8 +338,14 @@  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,