[PATCH v3 8/9] KVM: arm64: pkvm: Report optional ID register traps with a 0x18 syndrome

[Ben Horgan]

Hi Marc,

On 12/4/25 09:48, Marc Zyngier wrote:
> With FEAT_IDST, unimplemented system registers in the feature ID space
> must be reported using EC=0x18 at the closest handling EL, rather than
> with an UNDEF.
> 
> Most of these system registers are always implemented thanks to their
> dependency on FEAT_AA64, except for a set of (currently) three registers:
> GMID_EL1 (depending on MTE2), CCSIDR2_EL1 (depending on FEAT_CCIDX),
> and SMIDR_EL1 (depending on SME).
> 
> For these three registers, report their trap as EC=0x18 if they
> end-up trapping into KVM and that FEAT_IDST is implemented in the guest.
> Otherwise, just make them UNDEF.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> index 876b36d3d4788..efc36645f4b5a 100644
> --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> @@ -347,6 +347,18 @@ static bool pvm_gic_read_sre(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> +static bool pvm_idst_access(struct kvm_vcpu *vcpu,
> +			    struct sys_reg_params *p,
> +			    const struct sys_reg_desc *r)
> +{
> +	if (kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, NI))
> +		inject_undef64(vcpu);
> +	else
> +		inject_sync64(vcpu, kvm_vcpu_get_esr(vcpu));
> +
> +	return false;
> +}
> +

Just wondering, why is the pkvm version register specific? You changed
the non-pkvm from register specific to generic.

>  /* Mark the specified system register as an AArch32 feature id register. */
>  #define AARCH32(REG) { SYS_DESC(REG), .access = pvm_access_id_aarch32 }
>  
> @@ -472,6 +484,9 @@ static const struct sys_reg_desc pvm_sys_reg_descs[] = {
>  
>  	HOST_HANDLED(SYS_CCSIDR_EL1),
>  	HOST_HANDLED(SYS_CLIDR_EL1),
> +	{ SYS_DESC(SYS_CCSIDR2_EL1), .access = pvm_idst_access },
> +	{ SYS_DESC(SYS_GMID_EL1), .access = pvm_idst_access },
> +	{ SYS_DESC(SYS_SMIDR_EL1), .access = pvm_idst_access },
>  	HOST_HANDLED(SYS_AIDR_EL1),
>  	HOST_HANDLED(SYS_CSSELR_EL1),
>  	HOST_HANDLED(SYS_CTR_EL0),

Thanks,

Ben