KVM: arm64: Expose ID_AA64MMFR4_EL1 to guests

We can now expose ID_AA64MMFR4_EL1 to guests, and let NV guests
understand that they cannot really switch HCR_EL2.E2H to 0 on
some platforms.
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240122181344.258974-9-maz@kernel.orgSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kvm/nested.c

@@ -133,6 +133,13 @@ static u64 limit_nv_id_reg(u32 id, u64 val)
 		val |= FIELD_PREP(NV_FTR(MMFR2, TTL), 0b0001);
 		break;
 
+	case SYS_ID_AA64MMFR4_EL1:
+		val = 0;
+		if (!cpus_have_final_cap(ARM64_HAS_HCR_NV1))
+			val |= FIELD_PREP(NV_FTR(MMFR4, E2H0),
+					  ID_AA64MMFR4_EL1_E2H0_NI_NV1);
+		break;
+
 	case SYS_ID_AA64DFR0_EL1:
 		/* Only limited support for PMU, Debug, BPs and WPs */
 		val &= (NV_FTR(DFR0, PMUVer)	|

arch/arm64/kvm/sys_regs.c

@@ -2350,7 +2350,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 					ID_AA64MMFR2_EL1_NV |
 					ID_AA64MMFR2_EL1_CCIDX)),
 	ID_SANITISED(ID_AA64MMFR3_EL1),
-	ID_UNALLOCATED(7,4),
+	ID_SANITISED(ID_AA64MMFR4_EL1),
 	ID_UNALLOCATED(7,5),
 	ID_UNALLOCATED(7,6),
 	ID_UNALLOCATED(7,7),