[PATCH v2 4/5] KVM: arm64: Report optional ID register traps with a 0x18 syndrome

[Ben Horgan]

On 11/26/25 17:10, Ben Horgan wrote:
> Hi Marc,
> 
> On 11/26/25 15:59, 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 not implemented in the
>> guest. Otherwise, just make them UNDEF.
> 
> Missed it before but there is a stray 'not' in there. You get the
> EC=0x18 trap if FEAT_IDST is implemented.
> 
>>
>> Signed-off-by: Marc Zyngier <maz at kernel.org>
>> ---
>>  arch/arm64/kvm/sys_regs.c | 16 +++++++++++++---
>>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> The code looks good.
> 
> Reviewed-by: Ben Horgan

Just to complete that tag.

Reviewed-by: Ben Horgan <ben.horgan at arm.com>

> 
> Thanks,
> 
> Ben
> 
> 

-- 
Thanks,

Ben