KVM: MIPS/T&E: active_mm = init_mm in guest context

Set init_mm as the active_mm and update mm_cpumask(current->mm) to
reflect that it isn't active when in guest context. This prevents cache
management code from attempting cache flushes on host virtual addresses
while in guest context, for example due to a cache management IPIs or
later when writing of dynamically translated code hits copy on write.

We do this using helpers in static kernel code to avoid having to export
init_mm to modules.
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/include/asm/kvm_host.h

@@ -607,6 +607,10 @@ extern int kvm_mips_host_tlb_inv(struct kvm_vcpu *vcpu, unsigned long entryhi);
 extern int kvm_mips_guest_tlb_lookup(struct kvm_vcpu *vcpu,
 				     unsigned long entryhi);
 extern int kvm_mips_host_tlb_lookup(struct kvm_vcpu *vcpu, unsigned long vaddr);
+
+void kvm_mips_suspend_mm(int cpu);
+void kvm_mips_resume_mm(int cpu);
+
 extern unsigned long kvm_mips_translate_guest_kseg0_to_hpa(struct kvm_vcpu *vcpu,
 						   unsigned long gva);
 extern void kvm_get_new_mmu_context(struct mm_struct *mm, unsigned long cpu,

arch/mips/kvm/tlb.c

@@ -382,3 +382,38 @@ void kvm_local_flush_tlb_all(void)
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(kvm_local_flush_tlb_all);
+
+/**
+ * kvm_mips_suspend_mm() - Suspend the active mm.
+ * @cpu		The CPU we're running on.
+ *
+ * Suspend the active_mm, ready for a switch to a KVM guest virtual address
+ * space. This is left active for the duration of guest context, including time
+ * with interrupts enabled, so we need to be careful not to confuse e.g. cache
+ * management IPIs.
+ *
+ * kvm_mips_resume_mm() should be called before context switching to a different
+ * process so we don't need to worry about reference counting.
+ *
+ * This needs to be in static kernel code to avoid exporting init_mm.
+ */
+void kvm_mips_suspend_mm(int cpu)
+{
+	cpumask_clear_cpu(cpu, mm_cpumask(current->active_mm));
+	current->active_mm = &init_mm;
+}
+EXPORT_SYMBOL_GPL(kvm_mips_suspend_mm);
+
+/**
+ * kvm_mips_resume_mm() - Resume the current process mm.
+ * @cpu		The CPU we're running on.
+ *
+ * Resume the mm of the current process, after a switch back from a KVM guest
+ * virtual address space (see kvm_mips_suspend_mm()).
+ */
+void kvm_mips_resume_mm(int cpu)
+{
+	cpumask_set_cpu(cpu, mm_cpumask(current->mm));
+	current->active_mm = current->mm;
+}
+EXPORT_SYMBOL_GPL(kvm_mips_resume_mm);

arch/mips/kvm/trap_emul.c

@@ -670,6 +670,7 @@ static int kvm_trap_emul_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 			write_c0_entryhi(cpu_asid(cpu, kern_mm));
 		else
 			write_c0_entryhi(cpu_asid(cpu, user_mm));
+		kvm_mips_suspend_mm(cpu);
 		ehb();
 	}
 
@@ -689,6 +690,7 @@ static int kvm_trap_emul_vcpu_put(struct kvm_vcpu *vcpu, int cpu)
 			get_new_mmu_context(current->mm, cpu);
 		}
 		write_c0_entryhi(cpu_asid(cpu, current->mm));
+		kvm_mips_resume_mm(cpu);
 		ehb();
 	}
 
@@ -723,7 +725,7 @@ 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 cpu = smp_processor_id();
 	int r;
 
 	/* Check if we have any exceptions/interrupts pending */
@@ -735,6 +737,13 @@ static int kvm_trap_emul_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	/* Disable hardware page table walking while in guest */
 	htw_stop();
 
+	/*
+	 * While in guest context we're in the guest's address space, not the
+	 * host process address space, so we need to be careful not to confuse
+	 * e.g. cache management IPIs.
+	 */
+	kvm_mips_suspend_mm(cpu);
+
 	r = vcpu->arch.vcpu_run(run, vcpu);
 
 	/* We may have migrated while handling guest exits */
@@ -745,6 +754,7 @@ static int kvm_trap_emul_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	     asid_version_mask(cpu)))
 		get_new_mmu_context(current->mm, cpu);
 	write_c0_entryhi(cpu_asid(cpu, current->mm));
+	kvm_mips_resume_mm(cpu);
 
 	htw_start();