Re: [RFC PATCH v3 1/7] xen/arm: add generic SCI subsystem

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.03.2025 10:00, Oleksii Moisieiev wrote:
> Hi Jan,
> 
> Let me answer one of your comment. Please see below:
> 
> On 11/03/2025 13:43, Jan Beulich wrote:
>> On 11.03.2025 12:16, Grygorii Strashko wrote:
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -526,6 +526,12 @@ S:     Supported
>>>   F:        xen/arch/arm/include/asm/tee/
> [snip]
>>> --- a/xen/include/public/arch-arm.h
>>> +++ b/xen/include/public/arch-arm.h
>>> @@ -327,6 +327,8 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_guest_context_t);
>>>   #define XEN_DOMCTL_CONFIG_TEE_OPTEE     1
>>>   #define XEN_DOMCTL_CONFIG_TEE_FFA       2
>>>   
>>> +#define XEN_DOMCTL_CONFIG_ARM_SCI_NONE      0
>>> +
>>>   struct xen_arch_domainconfig {
>>>       /* IN/OUT */
>>>       uint8_t gic_version;
>>> @@ -350,6 +352,8 @@ struct xen_arch_domainconfig {
>>>        *
>>>        */
>>>       uint32_t clock_frequency;
>>> +    /* IN */
>>> +    uint8_t arm_sci_type;
>>>   };
>> You're not re-using a pre-existing padding field, so I don't see how you
>> can get away without bumping XEN_DOMCTL_INTERFACE_VERSION.
> 
> We are reusing an existing padding field in xen_domctl, which is defined 
> as pad[128].
> 
> The xen_arch_domainconfig structure is a part of the following domctl 
> structures:
> 
> - xen_domctl_createdomain
> 
> - xen_domctl_getdomaininfo
> 
> These structures are included in the union within xen_domctl, which 
> defines pad[128] for padding.

Except that "an existing padding field" means a field which isn't just
there in space, but is also checked to be zero right now. That is, new
code setting the field to non-zero needs to properly get an error
indicator back from an older hypervisor.

Jan