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

[Oleksii Moisieiev <Oleksii_Moisieiev@xxxxxxxx>]

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.
>
> Jan


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.

In the following example, I used the pahole tool to inspect the current 
structure sizes for the

xen_domctl structure:

 > pahole xen-syms -C xen_domctl

The result is as follows:

     struct xen_domctl {
             uint32_t                   cmd; /*     0     4 */
             uint32_t                   interface_version; /*     4     
4 */
             domid_t                    domain; /*     8     2 */
             uint16_t                   _pad[3];              /* 10     
6 */
             union {
                     struct xen_domctl_createdomain createdomain; /*    
16    76 */
                     struct xen_domctl_getdomaininfo getdomaininfo 
__attribute__((__aligned__(8))); /*    16   120 */
                     ...

                    uint8_t            pad[128];             /* 16   128 */

             };

Both structures, xen_domctl_createdomain and xen_domctl_getdomaininfo, 
do not exceed the size of the 128-byte padding.

WBR,

Oleksii.