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

[Oleksii Moisieiev <Oleksii_Moisieiev@xxxxxxxx>]

Hi Jan,

On 24/03/2025 12:05, Jan Beulich wrote:
> 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.

I completely agree with you that XEN_DOMCTL_INTERFACE_VERSION should be 
incremented

before the changes are merged. I just wanted to point out that we do not 
exceed the size of the xen_domctl padding. If you are okay with the 
fields we have added, then XEN_DOMCTL_INTERFACE_VERSION will be updated 
in the next patch series.

> but is also checked to be zero right now.

Just out of curiosity, I have one more question: I couldn't find the 
check you've mentioned. Could you point me to where Xen or

the toolstack checks the domctl structure for 0? I would greatly 
appreciate it if you could show me.


WBR,

Oleksii.