Re: [PATCH 08/26] 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.

--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c

@@ -251,14 +251,25 @@ 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;
+	}
+
+	crit = (crit_raw == crit_r1);