KVM: MIPS/T&E: Activate GVA page tables in guest context

Activate the GVA page tables when in guest context. This will allow the
normal Linux TLB refill handler to fill from it when guest memory is
read, as well as preventing accidental reading from user memory.
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/mmu_context.h

@@ -29,9 +29,11 @@ do {									\
 	}								\
 } while (0)
 
+extern void tlbmiss_handler_setup_pgd(unsigned long);
+
+/* Note: This is also implemented with uasm in arch/mips/kvm/entry.c */
 #define TLBMISS_HANDLER_SETUP_PGD(pgd)					\
 do {									\
-	extern void tlbmiss_handler_setup_pgd(unsigned long);		\
 	tlbmiss_handler_setup_pgd((unsigned long)(pgd));		\
 	htw_set_pwbase((unsigned long)pgd);				\
 } while (0)

arch/mips/kvm/entry.c

@@ -13,6 +13,7 @@
 
 #include <linux/kvm_host.h>
 #include <linux/log2.h>
+#include <asm/mmu_context.h>
 #include <asm/msa.h>
 #include <asm/setup.h>
 #include <asm/uasm.h>
@@ -316,7 +317,20 @@ static void *kvm_mips_build_enter_guest(void *addr)
 #else
 	uasm_i_andi(&p, K0, K0, MIPS_ENTRYHI_ASID);
 #endif
-	uasm_i_mtc0(&p, K0, C0_ENTRYHI);
+
+	/*
+	 * Set up KVM T&E GVA pgd.
+	 * This does roughly the same as TLBMISS_HANDLER_SETUP_PGD():
+	 * - call tlbmiss_handler_setup_pgd(mm->pgd)
+	 * - but skips write into CP0_PWBase for now
+	 */
+	UASM_i_LW(&p, A0, (int)offsetof(struct mm_struct, pgd) -
+			  (int)offsetof(struct mm_struct, context.asid), T1);
+
+	UASM_i_LA(&p, T9, (unsigned long)tlbmiss_handler_setup_pgd);
+	uasm_i_jalr(&p, RA, T9);
+	 uasm_i_mtc0(&p, K0, C0_ENTRYHI);
+
 	uasm_i_ehb(&p);
 
 	/* Disable RDHWR access */

arch/mips/kvm/trap_emul.c

@@ -704,6 +704,7 @@ static int kvm_trap_emul_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	struct mm_struct *kern_mm = &vcpu->arch.guest_kernel_mm;
 	struct mm_struct *user_mm = &vcpu->arch.guest_user_mm;
+	struct mm_struct *mm;
 
 	/* Allocate new kernel and user ASIDs if needed */
 
@@ -733,10 +734,9 @@ static int kvm_trap_emul_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	 * on the mode of the Guest (Kernel/User)
 	 */
 	if (current->flags & PF_VCPU) {
-		if (KVM_GUEST_KERNEL_MODE(vcpu))
-			write_c0_entryhi(cpu_asid(cpu, kern_mm));
-		else
-			write_c0_entryhi(cpu_asid(cpu, user_mm));
+		mm = KVM_GUEST_KERNEL_MODE(vcpu) ? kern_mm : user_mm;
+		write_c0_entryhi(cpu_asid(cpu, mm));
+		TLBMISS_HANDLER_SETUP_PGD(mm->pgd);
 		kvm_mips_suspend_mm(cpu);
 		ehb();
 	}
@@ -757,6 +757,7 @@ 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));
+		TLBMISS_HANDLER_SETUP_PGD(current->mm->pgd);
 		kvm_mips_resume_mm(cpu);
 		ehb();
 	}
@@ -821,6 +822,7 @@ 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));
+	TLBMISS_HANDLER_SETUP_PGD(current->mm->pgd);
 	kvm_mips_resume_mm(cpu);
 
 	htw_start();