[PATCH 06/11] KVM: x86: WARN if KVM emulates an IPI without clearing the BUSY flag

[Sean Christopherson <seanjc@google.com>]

WARN if KVM emulates an IPI without clearing the BUSY flag, failure to do
so could hang the guest if it waits for the IPI be sent.

Opportunistically use APIC_ICR_BUSY macro instead of open coding the
magic number, and add a comment to clarify why kvm_recalculate_apic_map()
is unconditionally invoked (it's really, really confusing for IPIs due to
the existence of fast paths that don't trigger a potential recalc).

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/lapic.c | 10 +++++++++-
 arch/x86/kvm/x86.c   |  9 ++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 6e1f9e83eb68..4f57b6f5ebd4 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1282,6 +1282,9 @@ void kvm_apic_send_ipi(struct kvm_lapic *apic, u32 icr_low, u32 icr_high)
 {
 	struct kvm_lapic_irq irq;
 
+	/* KVM has no delay and should always clear the BUSY/PENDING flag. */
+	WARN_ON_ONCE(icr_low & APIC_ICR_BUSY);
+
 	irq.vector = icr_low & APIC_VECTOR_MASK;
 	irq.delivery_mode = icr_low & APIC_MODE_MASK;
 	irq.dest_mode = icr_low & APIC_DEST_MASK;
@@ -2060,7 +2063,7 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 	}
 	case APIC_ICR:
 		/* No delay here, so we always clear the pending bit */
-		val &= ~(1 << 12);
+		val &= ~APIC_ICR_BUSY;
 		kvm_apic_send_ipi(apic, val, kvm_lapic_get_reg(apic, APIC_ICR2));
 		kvm_lapic_set_reg(apic, APIC_ICR, val);
 		break;
@@ -2139,6 +2142,11 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 		break;
 	}
 
+	/*
+	 * Recalculate APIC maps if necessary, e.g. if the software enable bit
+	 * was toggled, the APIC ID changed, etc...   The maps are marked dirty
+	 * on relevant changes, i.e. this is a nop for most writes.
+	 */
 	kvm_recalculate_apic_map(apic->vcpu->kvm);
 
 	return ret;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c25a6ef0ff06..9024e33c2add 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2012,11 +2012,10 @@ static int handle_fastpath_set_x2apic_icr_irqoff(struct kvm_vcpu *vcpu, u64 data
 		return 1;
 
 	if (((data & APIC_SHORT_MASK) == APIC_DEST_NOSHORT) &&
-		((data & APIC_DEST_MASK) == APIC_DEST_PHYSICAL) &&
-		((data & APIC_MODE_MASK) == APIC_DM_FIXED) &&
-		((u32)(data >> 32) != X2APIC_BROADCAST)) {
-
-		data &= ~(1 << 12);
+	    ((data & APIC_DEST_MASK) == APIC_DEST_PHYSICAL) &&
+	    ((data & APIC_MODE_MASK) == APIC_DM_FIXED) &&
+	    ((u32)(data >> 32) != X2APIC_BROADCAST)) {
+		data &= ~APIC_ICR_BUSY;
 		kvm_apic_send_ipi(vcpu->arch.apic, (u32)data, (u32)(data >> 32));
 		kvm_lapic_set_reg(vcpu->arch.apic, APIC_ICR2, (u32)(data >> 32));
 		kvm_lapic_set_reg(vcpu->arch.apic, APIC_ICR, (u32)data);
-- 
2.35.0.263.gb82422642f-goog