KVM: arm64: Get rid of reg_from/to_user()

These helpers are only used by the invariant stuff now, and while
they pretend to support non-64bit registers, this only serves as
a way to scare the casual reviewer...

Replace these helpers with our good friends get/put_user(), and
don't look back.
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/sys_regs.c

@@ -44,8 +44,6 @@
  * 64bit interface.
  */
 
-static int reg_from_user(u64 *val, const void __user *uaddr, u64 id);
-static int reg_to_user(void __user *uaddr, const u64 *val, u64 id);
 static u64 sys_reg_to_index(const struct sys_reg_desc *reg);
 
 static bool read_from_write_only(struct kvm_vcpu *vcpu,
@@ -2657,21 +2655,7 @@ static struct sys_reg_desc invariant_sys_regs[] = {
 	{ SYS_DESC(SYS_CTR_EL0), NULL, get_ctr_el0 },
 };
 
-static int reg_from_user(u64 *val, const void __user *uaddr, u64 id)
-{
-	if (copy_from_user(val, uaddr, KVM_REG_SIZE(id)) != 0)
-		return -EFAULT;
-	return 0;
-}
-
-static int reg_to_user(void __user *uaddr, const u64 *val, u64 id)
-{
-	if (copy_to_user(uaddr, val, KVM_REG_SIZE(id)) != 0)
-		return -EFAULT;
-	return 0;
-}
-
-static int get_invariant_sys_reg(u64 id, void __user *uaddr)
+static int get_invariant_sys_reg(u64 id, u64 __user *uaddr)
 {
 	const struct sys_reg_desc *r;
 
@@ -2680,23 +2664,21 @@ static int get_invariant_sys_reg(u64 id, void __user *uaddr)
 	if (!r)
 		return -ENOENT;
 
-	return reg_to_user(uaddr, &r->val, id);
+	return put_user(r->val, uaddr);
 }
 
-static int set_invariant_sys_reg(u64 id, void __user *uaddr)
+static int set_invariant_sys_reg(u64 id, u64 __user *uaddr)
 {
 	const struct sys_reg_desc *r;
-	int err;
-	u64 val = 0; /* Make sure high bits are 0 for 32-bit regs */
+	u64 val;
 
 	r = get_reg_by_id(id, invariant_sys_regs,
 			  ARRAY_SIZE(invariant_sys_regs));
 	if (!r)
 		return -ENOENT;
 
-	err = reg_from_user(&val, uaddr, id);
-	if (err)
-		return err;
+	if (get_user(val, uaddr))
+		return -EFAULT;
 
 	/* This is what we mean by invariant: you can't change it. */
 	if (r->val != val)