KVM: arm64: Add get_reg_by_id() as a sys_reg_desc retrieving helper

find_reg_by_id() requires a sys_reg_param as input, which most
users provide as a on-stack variable, but don't make any use of
the result.

Provide a helper that doesn't have this requirement and simplify
the callers (all but one).

Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/sys_regs.c

@@ -2650,21 +2650,29 @@ const struct sys_reg_desc *find_reg_by_id(u64 id,
 	return find_reg(params, table, num);
 }
 
+const struct sys_reg_desc *get_reg_by_id(u64 id,
+					 const struct sys_reg_desc table[],
+					 unsigned int num)
+{
+	struct sys_reg_params params;
+
+	if (!index_to_params(id, &params))
+		return NULL;
+
+	return find_reg(&params, table, num);
+}
+
 /* Decode an index value, and find the sys_reg_desc entry. */
 static const struct sys_reg_desc *index_to_sys_reg_desc(struct kvm_vcpu *vcpu,
 						    u64 id)
 {
 	const struct sys_reg_desc *r;
-	struct sys_reg_params params;
 
 	/* We only do sys_reg for now. */
 	if ((id & KVM_REG_ARM_COPROC_MASK) != KVM_REG_ARM64_SYSREG)
 		return NULL;
 
-	if (!index_to_params(id, &params))
+	r = get_reg_by_id(id, sys_reg_descs, ARRAY_SIZE(sys_reg_descs));
-		return NULL;
-
-	r = find_reg(&params, sys_reg_descs, ARRAY_SIZE(sys_reg_descs));
 
 	/* Not saved in the sys_reg array and not otherwise accessible? */
 	if (r && !(r->reg || r->get_user))
@@ -2723,11 +2731,10 @@ static int reg_to_user(void __user *uaddr, const u64 *val, u64 id)
 
 static int get_invariant_sys_reg(u64 id, void __user *uaddr)
 {
-	struct sys_reg_params params;
 	const struct sys_reg_desc *r;
 
-	r = find_reg_by_id(id, &params, invariant_sys_regs,
+	r = get_reg_by_id(id, invariant_sys_regs,
-			   ARRAY_SIZE(invariant_sys_regs));
+			  ARRAY_SIZE(invariant_sys_regs));
 	if (!r)
 		return -ENOENT;
 
@@ -2736,13 +2743,12 @@ static int get_invariant_sys_reg(u64 id, void __user *uaddr)
 
 static int set_invariant_sys_reg(u64 id, void __user *uaddr)
 {
-	struct sys_reg_params params;
 	const struct sys_reg_desc *r;
 	int err;
 	u64 val = 0; /* Make sure high bits are 0 for 32-bit regs */
 
-	r = find_reg_by_id(id, &params, invariant_sys_regs,
+	r = get_reg_by_id(id, invariant_sys_regs,
-			   ARRAY_SIZE(invariant_sys_regs));
+			  ARRAY_SIZE(invariant_sys_regs));
 	if (!r)
 		return -ENOENT;
 

arch/arm64/kvm/sys_regs.h

@@ -195,6 +195,10 @@ const struct sys_reg_desc *find_reg_by_id(u64 id,
 					  const struct sys_reg_desc table[],
 					  unsigned int num);
 
+const struct sys_reg_desc *get_reg_by_id(u64 id,
+					 const struct sys_reg_desc table[],
+					 unsigned int num);
+
 #define AA32(_x)	.aarch32_map = AA32_##_x
 #define Op0(_x) 	.Op0 = _x
 #define Op1(_x) 	.Op1 = _x

arch/arm64/kvm/vgic-sys-reg-v3.c

@@ -263,14 +263,10 @@ static const struct sys_reg_desc gic_v3_icc_reg_descs[] = {
 int vgic_v3_has_cpu_sysregs_attr(struct kvm_vcpu *vcpu, bool is_write, u64 id,
 				u64 *reg)
 {
-	struct sys_reg_params params;
 	u64 sysreg = (id & KVM_DEV_ARM_VGIC_SYSREG_MASK) | KVM_REG_SIZE_U64;
 
-	params.regval = *reg;
+	if (get_reg_by_id(sysreg, gic_v3_icc_reg_descs,
-	params.is_write = is_write;
+			  ARRAY_SIZE(gic_v3_icc_reg_descs)))
-
-	if (find_reg_by_id(sysreg, &params, gic_v3_icc_reg_descs,
-			      ARRAY_SIZE(gic_v3_icc_reg_descs)))
 		return 0;
 
 	return -ENXIO;