kvm: x86: Use fast CR3 switch for nested VMX

Use the fast CR3 switch mechanism to locklessly change the MMU root
page when switching between L1 and L2. The switch from L2 to L1 should
always go through the fast path, while the switch from L1 to L2 should
go through the fast path if L1's CR3/EPTP for L2 hasn't changed
since the last time.
Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -4054,7 +4054,7 @@ static bool fast_cr3_switch(struct kvm_vcpu *vcpu, gpa_t new_cr3,
 			return false;
 
 		swap(mmu->root_hpa, mmu->prev_root.hpa);
-		mmu->prev_root.cr3 = kvm_read_cr3(vcpu);
+		mmu->prev_root.cr3 = mmu->get_cr3(vcpu);
 
 		if (new_cr3 == prev_cr3 &&
 		    VALID_PAGE(mmu->root_hpa) &&
@@ -4091,6 +4091,7 @@ void kvm_mmu_new_cr3(struct kvm_vcpu *vcpu, gpa_t new_cr3)
 {
 	__kvm_mmu_new_cr3(vcpu, new_cr3, kvm_mmu_calc_root_page_role(vcpu));
 }
+EXPORT_SYMBOL_GPL(kvm_mmu_new_cr3);
 
 static unsigned long get_cr3(struct kvm_vcpu *vcpu)
 {
@@ -4725,12 +4726,13 @@ kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty)
 }
 
 void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
-			     bool accessed_dirty)
+			     bool accessed_dirty, gpa_t new_eptp)
 {
 	struct kvm_mmu *context = &vcpu->arch.mmu;
 	union kvm_mmu_page_role root_page_role =
 		kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty);
 
+	__kvm_mmu_new_cr3(vcpu, new_eptp, root_page_role);
 	context->shadow_root_level = PT64_ROOT_4LEVEL;
 
 	context->nx = true;

arch/x86/kvm/mmu.h

@@ -64,7 +64,7 @@ reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
 void kvm_init_mmu(struct kvm_vcpu *vcpu, bool reset_roots);
 void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu);
 void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
-			     bool accessed_dirty);
+			     bool accessed_dirty, gpa_t new_eptp);
 bool kvm_can_do_async_pf(struct kvm_vcpu *vcpu);
 int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
 				u64 fault_address, char *insn, int insn_len);

arch/x86/kvm/vmx.c

@@ -10741,11 +10741,11 @@ static int nested_ept_init_mmu_context(struct kvm_vcpu *vcpu)
 	if (!valid_ept_address(vcpu, nested_ept_get_cr3(vcpu)))
 		return 1;
 
-	kvm_mmu_unload(vcpu);
 	kvm_init_shadow_ept_mmu(vcpu,
 			to_vmx(vcpu)->nested.msrs.ept_caps &
 			VMX_EPT_EXECUTE_ONLY_BIT,
-			nested_ept_ad_enabled(vcpu));
+			nested_ept_ad_enabled(vcpu),
+			nested_ept_get_cr3(vcpu));
 	vcpu->arch.mmu.set_cr3           = vmx_set_cr3;
 	vcpu->arch.mmu.get_cr3           = nested_ept_get_cr3;
 	vcpu->arch.mmu.inject_page_fault = nested_ept_inject_page_fault;
@@ -11342,12 +11342,16 @@ static int nested_vmx_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3, bool ne
 				return 1;
 			}
 		}
-
-		vcpu->arch.cr3 = cr3;
-		__set_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail);
 	}
 
-	kvm_mmu_reset_context(vcpu);
+	if (!nested_ept)
+		kvm_mmu_new_cr3(vcpu, cr3);
+
+	vcpu->arch.cr3 = cr3;
+	__set_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail);
+
+	kvm_init_mmu(vcpu, false);
+
 	return 0;
 }
 

virt/kvm/kvm_main.c

@@ -2127,16 +2127,22 @@ static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu)
 
 static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
 {
+	int ret = -EINTR;
+	int idx = srcu_read_lock(&vcpu->kvm->srcu);
+
 	if (kvm_arch_vcpu_runnable(vcpu)) {
 		kvm_make_request(KVM_REQ_UNHALT, vcpu);
-		return -EINTR;
+		goto out;
 	}
 	if (kvm_cpu_has_pending_timer(vcpu))
-		return -EINTR;
+		goto out;
 	if (signal_pending(current))
-		return -EINTR;
+		goto out;
 
-	return 0;
+	ret = 0;
+out:
+	srcu_read_unlock(&vcpu->kvm->srcu, idx);
+	return ret;
 }
 
 /*