KVM: arm64: Correctly honor the presence of FEAT_TCRX

We currently blindly enable TCR2_EL1 use in a guest, irrespective
of the feature set. This is obviously wrong, and we should actually
honor the guest configuration and handle the possible trap resulting
from the guest being buggy.
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20240625130042.259175-2-maz@kernel.orgSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_arm.h

@@ -102,7 +102,7 @@
 #define HCR_HOST_NVHE_PROTECTED_FLAGS (HCR_HOST_NVHE_FLAGS | HCR_TSC)
 #define HCR_HOST_VHE_FLAGS (HCR_RW | HCR_TGE | HCR_E2H)
 
-#define HCRX_GUEST_FLAGS (HCRX_EL2_SMPME | HCRX_EL2_TCR2En)
+#define HCRX_GUEST_FLAGS (HCRX_EL2_SMPME)
 #define HCRX_HOST_FLAGS (HCRX_EL2_MSCEn | HCRX_EL2_TCR2En | HCRX_EL2_EnFPM)
 
 /* TCR_EL2 Registers bits */

arch/arm64/kvm/sys_regs.c

@@ -383,6 +383,12 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
 	bool was_enabled = vcpu_has_cache_enabled(vcpu);
 	u64 val, mask, shift;
 
+	if (reg_to_encoding(r) == SYS_TCR2_EL1 &&
+	    !kvm_has_feat(vcpu->kvm, ID_AA64MMFR3_EL1, TCRX, IMP)) {
+		kvm_inject_undefined(vcpu);
+		return false;
+	}
+
 	BUG_ON(!p->is_write);
 
 	get_access_mask(r, &mask, &shift);
@@ -4060,6 +4066,9 @@ void kvm_init_sysreg(struct kvm_vcpu *vcpu)
 
 		if (kvm_has_feat(kvm, ID_AA64ISAR2_EL1, MOPS, IMP))
 			vcpu->arch.hcrx_el2 |= (HCRX_EL2_MSCEn | HCRX_EL2_MCE2);
+
+		if (kvm_has_feat(kvm, ID_AA64MMFR3_EL1, TCRX, IMP))
+			vcpu->arch.hcrx_el2 |= HCRX_EL2_TCR2En;
 	}
 
 	if (test_bit(KVM_ARCH_FLAG_FGU_INITIALIZED, &kvm->arch.flags))