KVM: arm64: Expose S1PIE to guests

Prior to commit 70ed7238 ("KVM: arm64: Sanitise ID_AA64MMFR3_EL1")
we just exposed the santised view of ID_AA64MMFR3_EL1 to guests, meaning
that they saw both TCRX and S1PIE if present on the host machine. That
commit added VMM control over the contents of the register and exposed
S1POE but removed S1PIE, meaning that the extension is no longer visible
to guests. Reenable support for S1PIE with VMM control.

Fixes: 70ed7238 ("KVM: arm64: Sanitise ID_AA64MMFR3_EL1")
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20241005-kvm-arm64-fix-s1pie-v1-1-5901f02de749@kernel.orgSigned-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/sys_regs.c

@@ -1558,7 +1558,8 @@ static u64 __kvm_read_sanitised_id_reg(const struct kvm_vcpu *vcpu,
 		val &= ~ID_AA64MMFR2_EL1_CCIDX_MASK;
 		break;
 	case SYS_ID_AA64MMFR3_EL1:
-		val &= ID_AA64MMFR3_EL1_TCRX | ID_AA64MMFR3_EL1_S1POE;
+		val &= ID_AA64MMFR3_EL1_TCRX | ID_AA64MMFR3_EL1_S1POE |
+			ID_AA64MMFR3_EL1_S1PIE;
 		break;
 	case SYS_ID_MMFR4_EL1:
 		val &= ~ARM64_FEATURE_MASK(ID_MMFR4_EL1_CCIDX);
@@ -2467,6 +2468,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 					ID_AA64MMFR2_EL1_NV |
 					ID_AA64MMFR2_EL1_CCIDX)),
 	ID_WRITABLE(ID_AA64MMFR3_EL1, (ID_AA64MMFR3_EL1_TCRX	|
+				       ID_AA64MMFR3_EL1_S1PIE   |
 				       ID_AA64MMFR3_EL1_S1POE)),
 	ID_SANITISED(ID_AA64MMFR4_EL1),
 	ID_UNALLOCATED(7,5),