KVM: MIPS: Update vcpu->mode and vcpu->cpu

Keep the vcpu->mode and vcpu->cpu variables up to date so that
kvm_make_all_cpus_request() has a chance of functioning correctly. This
will soon need to be used for kvm_flush_remote_tlbs().

We can easily update vcpu->cpu when the VCPU context is loaded or saved,
which will happen when accessing guest context and when the guest is
scheduled in and out.

We need to be a little careful with vcpu->mode though, as we will in
future be checking for outstanding VCPU requests, and this must be done
after the value of IN_GUEST_MODE in vcpu->mode is visible to other CPUs.
Otherwise the other CPU could fail to trigger an IPI to wait for
completion dispite the VCPU request not being seen.
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org

arch/mips/kvm/mips.c

@@ -365,6 +365,14 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	guest_enter_irqoff();
 	trace_kvm_enter(vcpu);
 
+	/*
+	 * Make sure the read of VCPU requests in vcpu_run() callback is not
+	 * reordered ahead of the write to vcpu->mode, or we could miss a TLB
+	 * flush request while the requester sees the VCPU as outside of guest
+	 * mode and not needing an IPI.
+	 */
+	smp_store_mb(vcpu->mode, IN_GUEST_MODE);
+
 	r = kvm_mips_callbacks->vcpu_run(run, vcpu);
 
 	trace_kvm_out(vcpu);
@@ -1326,6 +1334,8 @@ int kvm_mips_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	u32 inst;
 	int ret = RESUME_GUEST;
 
+	vcpu->mode = OUTSIDE_GUEST_MODE;
+
 	/* re-enable HTW before enabling interrupts */
 	htw_start();
 
@@ -1481,6 +1491,14 @@ int kvm_mips_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	if (ret == RESUME_GUEST) {
 		trace_kvm_reenter(vcpu);
 
+		/*
+		 * Make sure the read of VCPU requests in vcpu_reenter()
+		 * callback is not reordered ahead of the write to vcpu->mode,
+		 * or we could miss a TLB flush request while the requester sees
+		 * the VCPU as outside of guest mode and not needing an IPI.
+		 */
+		smp_store_mb(vcpu->mode, IN_GUEST_MODE);
+
 		kvm_mips_callbacks->vcpu_reenter(run, vcpu);
 
 		/*

arch/mips/kvm/mmu.c

@@ -696,6 +696,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
 	local_irq_save(flags);
 
+	vcpu->cpu = cpu;
 	if (vcpu->arch.last_sched_cpu != cpu) {
 		kvm_debug("[%d->%d]KVM VCPU[%d] switch\n",
 			  vcpu->arch.last_sched_cpu, cpu, vcpu->vcpu_id);
@@ -723,6 +724,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 
 	cpu = smp_processor_id();
 	vcpu->arch.last_sched_cpu = cpu;
+	vcpu->cpu = -1;
 
 	/* save guest state in registers */
 	kvm_mips_callbacks->vcpu_put(vcpu, cpu);