KVM: x86: add a flag to disable KVM x2apic broadcast quirk
Add KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK as a feature flag to
KVM_CAP_X2APIC_API.
The quirk made KVM interpret 0xff as a broadcast even in x2APIC mode.
The enableable capability is needed in order to support standard x2APIC and
remain backward compatible.
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
[Expand kvm_apic_mda comment. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index d27a782..a16e0bb 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -616,17 +616,30 @@
}
}
-/* KVM APIC implementation has two quirks
- * - dest always begins at 0 while xAPIC MDA has offset 24,
- * - IOxAPIC messages have to be delivered (directly) to x2APIC.
+/* The KVM local APIC implementation has two quirks:
+ *
+ * - the xAPIC MDA stores the destination at bits 24-31, while this
+ * is not true of struct kvm_lapic_irq's dest_id field. This is
+ * just a quirk in the API and is not problematic.
+ *
+ * - in-kernel IOAPIC messages have to be delivered directly to
+ * x2APIC, because the kernel does not support interrupt remapping.
+ * In order to support broadcast without interrupt remapping, x2APIC
+ * rewrites the destination of non-IPI messages from APIC_BROADCAST
+ * to X2APIC_BROADCAST.
+ *
+ * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API. This is
+ * important when userspace wants to use x2APIC-format MSIs, because
+ * APIC_BROADCAST (0xff) is a legal route for "cluster 0, CPUs 0-7".
*/
-static u32 kvm_apic_mda(unsigned int dest_id, struct kvm_lapic *source,
- struct kvm_lapic *target)
+static u32 kvm_apic_mda(struct kvm_vcpu *vcpu, unsigned int dest_id,
+ struct kvm_lapic *source, struct kvm_lapic *target)
{
bool ipi = source != NULL;
bool x2apic_mda = apic_x2apic_mode(ipi ? source : target);
- if (!ipi && dest_id == APIC_BROADCAST && x2apic_mda)
+ if (!vcpu->kvm->arch.x2apic_broadcast_quirk_disabled &&
+ !ipi && dest_id == APIC_BROADCAST && x2apic_mda)
return X2APIC_BROADCAST;
return x2apic_mda ? dest_id : SET_APIC_DEST_FIELD(dest_id);
@@ -636,7 +649,7 @@
int short_hand, unsigned int dest, int dest_mode)
{
struct kvm_lapic *target = vcpu->arch.apic;
- u32 mda = kvm_apic_mda(dest, source, target);
+ u32 mda = kvm_apic_mda(vcpu, dest, source, target);
apic_debug("target %p, source %p, dest 0x%x, "
"dest_mode 0x%x, short_hand 0x%x\n",
@@ -688,6 +701,25 @@
}
}
+static bool kvm_apic_is_broadcast_dest(struct kvm *kvm, struct kvm_lapic **src,
+ struct kvm_lapic_irq *irq, struct kvm_apic_map *map)
+{
+ if (kvm->arch.x2apic_broadcast_quirk_disabled) {
+ if ((irq->dest_id == APIC_BROADCAST &&
+ map->mode != KVM_APIC_MODE_X2APIC))
+ return true;
+ if (irq->dest_id == X2APIC_BROADCAST)
+ return true;
+ } else {
+ bool x2apic_ipi = src && *src && apic_x2apic_mode(*src);
+ if (irq->dest_id == (x2apic_ipi ?
+ X2APIC_BROADCAST : APIC_BROADCAST))
+ return true;
+ }
+
+ return false;
+}
+
/* Return true if the interrupt can be handled by using *bitmap as index mask
* for valid destinations in *dst array.
* Return false if kvm_apic_map_get_dest_lapic did nothing useful.
@@ -701,7 +733,6 @@
unsigned long *bitmap)
{
int i, lowest;
- bool x2apic_ipi;
if (irq->shorthand == APIC_DEST_SELF && src) {
*dst = src;
@@ -710,11 +741,7 @@
} else if (irq->shorthand)
return false;
- x2apic_ipi = src && *src && apic_x2apic_mode(*src);
- if (irq->dest_id == (x2apic_ipi ? X2APIC_BROADCAST : APIC_BROADCAST))
- return false;
-
- if (!map)
+ if (!map || kvm_apic_is_broadcast_dest(kvm, src, irq, map))
return false;
if (irq->dest_mode == APIC_DEST_PHYSICAL) {