KVM: arm64: Copy guest CTR_EL0 into hyp VM

Since commit 2843cae ("KVM: arm64: Treat CTR_EL0 as a VM feature
ID register") KVM has allowed userspace to configure the VM-wide view of
CTR_EL0, falling back to trap-n-emulate if the value doesn't match
hardware. It appears that this has worked by chance in protected-mode
for some time, and on systems with FEAT_EVT protected-mode
unconditionally sets TID4 (i.e. TID2 traps sans CTR_EL0).

Forward the guest CTR_EL0 value through to the hyp VM and align the
TID2/TID4 configuration with the non-protected setup.

Fixes: 2843cae ("KVM: arm64: Treat CTR_EL0 as a VM feature ID register")
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250305230825.484091-2-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: oupton

arch/arm64/kvm/hyp/nvhe/pkvm.c

@@ -46,7 +46,8 @@ static void pkvm_vcpu_reset_hcr(struct kvm_vcpu *vcpu)
 		vcpu->arch.hcr_el2 |= HCR_FWB;
 
 	if (cpus_have_final_cap(ARM64_HAS_EVT) &&
-	    !cpus_have_final_cap(ARM64_MISMATCHED_CACHE_TYPE))
+	    !cpus_have_final_cap(ARM64_MISMATCHED_CACHE_TYPE) &&
+	    kvm_read_vm_id_reg(vcpu->kvm, SYS_CTR_EL0) == read_cpuid(CTR_EL0))
 		vcpu->arch.hcr_el2 |= HCR_TID4;
 	else
 		vcpu->arch.hcr_el2 |= HCR_TID2;
@@ -315,6 +316,9 @@ static void pkvm_init_features_from_host(struct pkvm_hyp_vm *hyp_vm, const struc
 	unsigned long host_arch_flags = READ_ONCE(host_kvm->arch.flags);
 	DECLARE_BITMAP(allowed_features, KVM_VCPU_MAX_FEATURES);
 
+	/* CTR_EL0 is always under host control, even for protected VMs. */
+	hyp_vm->kvm.arch.ctr_el0 = host_kvm->arch.ctr_el0;
+
 	if (test_bit(KVM_ARCH_FLAG_MTE_ENABLED, &host_kvm->arch.flags))
 		set_bit(KVM_ARCH_FLAG_MTE_ENABLED, &kvm->arch.flags);