Re: [PATCH v2 3/3] arm/kvm: get demuxed ID registers from kvm

[Cornelia Huck <cohuck@redhat.com>]

On Wed, Apr 01 2026, Eric Auger <eric.auger@redhat.com> wrote:

> On 2/4/26 2:32 PM, Cornelia Huck wrote:
>> We now have the infrastructure in place to get and save demuxed ID
> Here we only get their values? What about the save?

We only get, but we could also save, if we had the right interfaces :)
I'll try to reword it to be less confusing.

>> registers from kvm. Use it to get the values that kvm emulates for
>> CCSIDR_EL1.
>>
>> Tested-by: Alireza Sanaee <alireza.sanaee@huawei.com>
>> Reviewed-by: Sebastian Ott <sebott@redhat.com>
>> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
>> ---
>>  target/arm/kvm.c | 33 +++++++++++++++++++++++++++++++++
>>  1 file changed, 33 insertions(+)
>>
>> @@ -416,6 +444,11 @@ static bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
>>               */
>>              err |= get_host_cpu_reg(fd, ahcf, ID_AA64ZFR0_EL1_IDX);
>>          }
>> +        /* grab demuxed registers */
>> +        for (i = 0; i < 14; i++) {
>> +            /* KVM only allows 0..13 */
> where is it documented? Maybe add a comment or justification in the
> commit msg. Use a define?

Linux arch/arm64/kvm/sys_regs.c has

#define CSSELR_MAX 14

Not sure if there is any actual documentation.

>> +            err |= get_host_cpu_reg_demux(fd, ahcf, CCSIDR_EL1_IDX, i);
>> +        }
>>      }
>>  
>>      kvm_arm_destroy_scratch_host_vcpu(fdarray);
> Thanks
>
> Eric