KVM: x86/xen: latch long_mode when hypercall page is set up

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

arch/x86/include/asm/kvm_host.h

@@ -905,6 +905,11 @@ struct msr_bitmap_range {
 	unsigned long *bitmap;
 };
 
+/* Xen emulation context */
+struct kvm_xen {
+	bool long_mode;
+};
+
 enum kvm_irqchip_mode {
 	KVM_IRQCHIP_NONE,
 	KVM_IRQCHIP_KERNEL,       /* created with KVM_CREATE_IRQCHIP */
@@ -984,6 +989,7 @@ struct kvm_arch {
 	struct hlist_head mask_notifier_list;
 
 	struct kvm_hv hyperv;
+	struct kvm_xen xen;
 
 	#ifdef CONFIG_KVM_MMU_AUDIT
 	int audit_point;

arch/x86/kvm/xen.c

@@ -25,6 +25,13 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 	mutex_unlock(&kvm->lock);
 
 	switch (data->type) {
+	case KVM_XEN_ATTR_TYPE_LONG_MODE:
+		if (!IS_ENABLED(CONFIG_64BIT) && data->u.long_mode)
+			return -EINVAL;
+
+		kvm->arch.xen.long_mode = !!data->u.long_mode;
+		r = 0;
+		break;
 	default:
 		break;
 	}
@@ -40,6 +47,10 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 	mutex_lock(&kvm->lock);
 
 	switch (data->type) {
+	case KVM_XEN_ATTR_TYPE_LONG_MODE:
+		data->u.long_mode = kvm->arch.xen.long_mode;
+		r = 0;
+		break;
 	default:
 		break;
 	}
@@ -53,6 +64,10 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
 	struct kvm *kvm = vcpu->kvm;
 	u32 page_num = data & ~PAGE_MASK;
 	u64 page_addr = data & PAGE_MASK;
+	bool lm = is_long_mode(vcpu);
+
+	/* Latch long_mode for shared_info pages etc. */
+	vcpu->kvm->arch.xen.long_mode = lm;
 
 	/*
 	 * If Xen hypercall intercept is enabled, fill the hypercall
@@ -87,7 +102,6 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
 				return 1;
 		}
 	} else {
-		int lm = is_long_mode(vcpu);
 		u64 blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
 				   : kvm->arch.xen_hvm_config.blob_addr_32;
 		u8 blob_size = lm ? kvm->arch.xen_hvm_config.blob_size_64

include/uapi/linux/kvm.h

@@ -1594,10 +1594,13 @@ struct kvm_xen_hvm_attr {
 	__u16 type;
 	__u16 pad[3];
 	union {
+		__u8 long_mode;
 		__u64 pad[8];
 	} u;
 };
 
+#define KVM_XEN_ATTR_TYPE_LONG_MODE		0x0
+
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {
 	/* Guest initialization commands */