KVM: MIPS/T&E: Restore host asid on return to host

We only need the guest ASID loaded while in guest context, i.e. while
running guest code and while handling guest exits. We load the guest
ASID when entering the guest, however we restore the host ASID later
than necessary, when the VCPU state is saved i.e. vcpu_put() or slightly
earlier if preempted after returning to the host.

This mismatch is both unpleasant and causes redundant host ASID restores
in kvm_trap_emul_vcpu_put(). Lets explicitly restore the host ASID when
returning to the host, and don't bother restoring the host ASID on
context switch in unless we're already in guest context.

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/trap_emul.c

@@ -680,14 +680,17 @@ static int kvm_trap_emul_vcpu_put(struct kvm_vcpu *vcpu, int cpu)
 {
 	kvm_lose_fpu(vcpu);
 
-	if (((cpu_context(cpu, current->mm) ^ asid_cache(cpu)) &
-	     asid_version_mask(cpu))) {
-		kvm_debug("%s: Dropping MMU Context:  %#lx\n", __func__,
-			  cpu_context(cpu, current->mm));
-		drop_mmu_context(current->mm, cpu);
+	if (current->flags & PF_VCPU) {
+		/* Restore normal Linux process memory map */
+		if (((cpu_context(cpu, current->mm) ^ asid_cache(cpu)) &
+		     asid_version_mask(cpu))) {
+			kvm_debug("%s: Dropping MMU Context:  %#lx\n", __func__,
+				  cpu_context(cpu, current->mm));
+			get_new_mmu_context(current->mm, cpu);
+		}
+		write_c0_entryhi(cpu_asid(cpu, current->mm));
+		ehb();
 	}
-	write_c0_entryhi(cpu_asid(cpu, current->mm));
-	ehb();
 
 	return 0;
 }
@@ -720,6 +723,7 @@ static void kvm_trap_emul_vcpu_reenter(struct kvm_run *run,
 
 static int kvm_trap_emul_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu)
 {
+	int cpu;
 	int r;
 
 	/* Check if we have any exceptions/interrupts pending */
@@ -733,6 +737,15 @@ static int kvm_trap_emul_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu)
 
 	r = vcpu->arch.vcpu_run(run, vcpu);
 
+	/* We may have migrated while handling guest exits */
+	cpu = smp_processor_id();
+
+	/* Restore normal Linux process memory map */
+	if (((cpu_context(cpu, current->mm) ^ asid_cache(cpu)) &
+	     asid_version_mask(cpu)))
+		get_new_mmu_context(current->mm, cpu);
+	write_c0_entryhi(cpu_asid(cpu, current->mm));
+
 	htw_start();
 
 	return r;