[PATCH v2 1/4] KVM: x86: use MDA for interrupt matching

["Radim Krčmář" <rkrcmar@redhat.com>]

In mixed modes, we musn't deliver xAPIC IPIs like x2APIC and vice versa.
Instead of preserving the information in apic_send_ipi(), we regain it
by converting all destinations into correct MDA in the slow path.
This allows easier reasoning about subsequent matching.

Our kvm_apic_broadcast() had an interesting design decision: it didn't
consider IOxAPIC 0xff as broadcast in x2APIC mode ...
everything worked because IOxAPIC can't set that in physical mode and
logical mode considered it as a message for first 8 VCPUs.
This patch interprets IOxAPIC 0xff as x2APIC broadcast.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v2
 - accept two 'struct lapic *' in kvm_apic_mda() for nicer code [Paolo]
 - removed XXX comment about checking if x2APIC broadcast is accepted
   (it is, and the code also accepts any x2APIC message starting with
    0xff, like v1, for simplicity.)


 arch/x86/kvm/lapic.c | 40 +++++++++++++++++++++++++++++++++-------
 1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 86609c15726f..4812bde5090c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -585,15 +585,23 @@ static void apic_set_tpr(struct kvm_lapic *apic, u32 tpr)
 	apic_update_ppr(apic);
 }
 
-static bool kvm_apic_broadcast(struct kvm_lapic *apic, u32 dest)
+static bool kvm_apic_broadcast(struct kvm_lapic *apic, u32 mda)
 {
-	return dest == (apic_x2apic_mode(apic) ?
-			X2APIC_BROADCAST : APIC_BROADCAST);
+	if (apic_x2apic_mode(apic))
+		return mda == X2APIC_BROADCAST;
+
+	return GET_APIC_DEST_FIELD(mda) == APIC_BROADCAST;
 }
 
-static bool kvm_apic_match_physical_addr(struct kvm_lapic *apic, u32 dest)
+static bool kvm_apic_match_physical_addr(struct kvm_lapic *apic, u32 mda)
 {
-	return kvm_apic_id(apic) == dest || kvm_apic_broadcast(apic, dest);
+	if (kvm_apic_broadcast(apic, mda))
+		return true;
+
+	if (apic_x2apic_mode(apic))
+		return mda == kvm_apic_id(apic);
+
+	return mda == SET_APIC_DEST_FIELD(kvm_apic_id(apic));
 }
 
 static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
@@ -610,6 +618,7 @@ static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
 		       && (logical_id & mda & 0xffff) != 0;
 
 	logical_id = GET_APIC_LOGICAL_ID(logical_id);
+	mda = GET_APIC_DEST_FIELD(mda);
 
 	switch (kvm_apic_get_reg(apic, APIC_DFR)) {
 	case APIC_DFR_FLAT:
@@ -624,10 +633,27 @@ static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
 	}
 }
 
+/* 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.
+ */
+static u32 kvm_apic_mda(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)
+		return X2APIC_BROADCAST;
+
+	return x2apic_mda ? dest_id : SET_APIC_DEST_FIELD(dest_id);
+}
+
 bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 			   int short_hand, unsigned int dest, int dest_mode)
 {
 	struct kvm_lapic *target = vcpu->arch.apic;
+	u32 mda = kvm_apic_mda(dest, source, target);
 
 	apic_debug("target %p, source %p, dest 0x%x, "
 		   "dest_mode 0x%x, short_hand 0x%x\n",
@@ -637,9 +663,9 @@ bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 	switch (short_hand) {
 	case APIC_DEST_NOSHORT:
 		if (dest_mode == APIC_DEST_PHYSICAL)
-			return kvm_apic_match_physical_addr(target, dest);
+			return kvm_apic_match_physical_addr(target, mda);
 		else
-			return kvm_apic_match_logical_addr(target, dest);
+			return kvm_apic_match_logical_addr(target, mda);
 	case APIC_DEST_SELF:
 		return target == source;
 	case APIC_DEST_ALLINC:
-- 
2.3.0