KVM: PPC: Add PV guest critical sections

When running in hooked code we need a way to disable interrupts without
clobbering any interrupts or exiting out to the hypervisor.

To achieve this, we have an additional critical field in the shared page. If
that field is equal to the r1 register of the guest, it tells the hypervisor
that we're in such a critical section and thus may not receive any interrupts.
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/powerpc/include/asm/kvm_para.h

@@ -24,6 +24,7 @@
 #include <linux/of.h>
 
 struct kvm_vcpu_arch_shared {
+	__u64 critical;		/* Guest may not get interrupts if == r1 */
 	__u64 sprg0;
 	__u64 sprg1;
 	__u64 sprg2;

arch/powerpc/kvm/book3s.c

@@ -251,14 +251,28 @@ int kvmppc_book3s_irqprio_deliver(struct kvm_vcpu *vcpu, unsigned int priority)
 	int deliver = 1;
 	int vec = 0;
 	ulong flags = 0ULL;
+	ulong crit_raw = vcpu->arch.shared->critical;
+	ulong crit_r1 = kvmppc_get_gpr(vcpu, 1);
+	bool crit;
+
+	/* Truncate crit indicators in 32 bit mode */
+	if (!(vcpu->arch.shared->msr & MSR_SF)) {
+		crit_raw &= 0xffffffff;
+		crit_r1 &= 0xffffffff;
+	}
+
+	/* Critical section when crit == r1 */
+	crit = (crit_raw == crit_r1);
+	/* ... and we're in supervisor mode */
+	crit = crit && !(vcpu->arch.shared->msr & MSR_PR);
 
 	switch (priority) {
 	case BOOK3S_IRQPRIO_DECREMENTER:
-		deliver = vcpu->arch.shared->msr & MSR_EE;
+		deliver = (vcpu->arch.shared->msr & MSR_EE) && !crit;
 		vec = BOOK3S_INTERRUPT_DECREMENTER;
 		break;
 	case BOOK3S_IRQPRIO_EXTERNAL:
-		deliver = vcpu->arch.shared->msr & MSR_EE;
+		deliver = (vcpu->arch.shared->msr & MSR_EE) && !crit;
 		vec = BOOK3S_INTERRUPT_EXTERNAL;
 		break;
 	case BOOK3S_IRQPRIO_SYSTEM_RESET:

arch/powerpc/kvm/booke.c

@@ -147,6 +147,20 @@ static int kvmppc_booke_irqprio_deliver(struct kvm_vcpu *vcpu,
 	int allowed = 0;
 	ulong uninitialized_var(msr_mask);
 	bool update_esr = false, update_dear = false;
+	ulong crit_raw = vcpu->arch.shared->critical;
+	ulong crit_r1 = kvmppc_get_gpr(vcpu, 1);
+	bool crit;
+
+	/* Truncate crit indicators in 32 bit mode */
+	if (!(vcpu->arch.shared->msr & MSR_SF)) {
+		crit_raw &= 0xffffffff;
+		crit_r1 &= 0xffffffff;
+	}
+
+	/* Critical section when crit == r1 */
+	crit = (crit_raw == crit_r1);
+	/* ... and we're in supervisor mode */
+	crit = crit && !(vcpu->arch.shared->msr & MSR_PR);
 
 	switch (priority) {
 	case BOOKE_IRQPRIO_DTLB_MISS:
@@ -181,6 +195,7 @@ static int kvmppc_booke_irqprio_deliver(struct kvm_vcpu *vcpu,
 	case BOOKE_IRQPRIO_DECREMENTER:
 	case BOOKE_IRQPRIO_FIT:
 		allowed = vcpu->arch.shared->msr & MSR_EE;
+		allowed = allowed && !crit;
 		msr_mask = MSR_CE|MSR_ME|MSR_DE;
 		break;
 	case BOOKE_IRQPRIO_DEBUG: