KVM: arm64: nv: Move TLBI range decoding to a helper

As we are about to expand out TLB invalidation capabilities to support
recursive virtualisation, move the decoding of a TLBI by range into
a helper that returns the base, the range and the ASID.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250514103501.2225951-6-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Marc Zyngier

arch/arm64/include/asm/kvm_nested.h

@@ -231,6 +231,38 @@ static inline u64 kvm_encode_nested_level(struct kvm_s2_trans *trans)
 		shift;							\
 	})
 
+static inline u64 decode_range_tlbi(u64 val, u64 *range, u16 *asid)
+{
+	u64 base, tg, num, scale;
+	int shift;
+
+	tg	= FIELD_GET(GENMASK(47, 46), val);
+
+	switch(tg) {
+	case 1:
+		shift = 12;
+		break;
+	case 2:
+		shift = 14;
+		break;
+	case 3:
+	default:		/* IMPDEF: handle tg==0 as 64k */
+		shift = 16;
+		break;
+	}
+
+	base	= (val & GENMASK(36, 0)) << shift;
+
+	if (asid)
+		*asid = FIELD_GET(TLBIR_ASID_MASK, val);
+
+	scale	= FIELD_GET(GENMASK(45, 44), val);
+	num	= FIELD_GET(GENMASK(43, 39), val);
+	*range	= __TLBI_RANGE_PAGES(num, scale) << shift;
+
+	return base;
+}
+
 static inline unsigned int ps_to_output_size(unsigned int ps)
 {
 	switch (ps) {

arch/arm64/kvm/sys_regs.c

@@ -3546,8 +3546,7 @@ static bool handle_ripas2e1is(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 {
 	u32 sys_encoding = sys_insn(p->Op0, p->Op1, p->CRn, p->CRm, p->Op2);
 	u64 vttbr = vcpu_read_sys_reg(vcpu, VTTBR_EL2);
-	u64 base, range, tg, num, scale;
-	int shift;
+	u64 base, range;
 
 	if (!kvm_supported_tlbi_ipas2_op(vcpu, sys_encoding))
 		return undef_access(vcpu, p, r);
@@ -3557,26 +3556,7 @@ static bool handle_ripas2e1is(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 	 * of the guest's S2 (different base granule size, for example), we
 	 * decide to ignore TTL and only use the described range.
 	 */
-	tg	= FIELD_GET(GENMASK(47, 46), p->regval);
-	scale	= FIELD_GET(GENMASK(45, 44), p->regval);
-	num	= FIELD_GET(GENMASK(43, 39), p->regval);
-	base	= p->regval & GENMASK(36, 0);
-
-	switch(tg) {
-	case 1:
-		shift = 12;
-		break;
-	case 2:
-		shift = 14;
-		break;
-	case 3:
-	default:		/* IMPDEF: handle tg==0 as 64k */
-		shift = 16;
-		break;
-	}
-
-	base <<= shift;
-	range = __TLBI_RANGE_PAGES(num, scale) << shift;
+	base = decode_range_tlbi(p->regval, &range, NULL);
 
 	kvm_s2_mmu_iterate_by_vmid(vcpu->kvm, get_vmid(vttbr),
 				   &(union tlbi_info) {