Re: [PATCH 1/3] KVM: arm64: Copy guest CTR_EL0 into hyp VM

[Marc Zyngier <maz@kernel.org>]

On Wed, 05 Mar 2025 23:08:23 +0000,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> Since commit 2843cae26644 ("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: 2843cae26644 ("KVM: arm64: Treat CTR_EL0 as a VM feature ID register")
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  arch/arm64/kvm/hyp/nvhe/pkvm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
> index 3927fe52a3dd..2e2975248cd3 100644
> --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
> +++ b/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;
> @@ -374,6 +375,7 @@ static void init_pkvm_hyp_vm(struct kvm *host_kvm, struct pkvm_hyp_vm *hyp_vm,
>  	hyp_vm->kvm.arch.pkvm.enabled = READ_ONCE(host_kvm->arch.pkvm.enabled);
>  	hyp_vm->kvm.arch.flags = 0;
>  	pkvm_init_features_from_host(hyp_vm, host_kvm);
> +	hyp_vm->kvm.arch.ctr_el0 = host_kvm->arch.ctr_el0;

Maybe it'd be better to stick this into pkvm_init_features_from_host()
in order to keep all the "inherit stuff from host" together?

Same thing for the following patch.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.