Re: [PATCH for-4.22] XSM: guard .sysctl() and .readconsole() hooks

[Jan Beulich <jbeulich@xxxxxxxx>]

On 18.06.2026 14:34, Daniel P. Smith wrote:
> On 6/18/26 8:23 AM, Jan Beulich wrote:
>> On 18.06.2026 14:13, Andrew Cooper wrote:
>>> On 18/06/2026 12:32 pm, Jan Beulich wrote:
>>>> Leaving the hook pointers in struct xsm_ops when !SYSCTL would lead to
>>>> the BUG_ON() in xsm_fixup_ops() triggering for respectively configured
>>>> hypervisors.
>>>>
>>>> While moving the #ifdef for the corresponding xsm_*() wrappers, also move
>>>> those for xsm_page_offline() (where the hook pointer field already is
>>>> suitably guarded).
>>>>
>>>> Fixes: c9eabaa03a68 ("xen/xsm: wrap around xsm_sysctl with CONFIG_SYSCTL")
>>>> Fixes: bddd9af6049f ("xen/sysctl: wrap around XEN_SYSCTL_readconsole")
>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>
>>> Ugly.  We probably ought to see about booting the RANDCONFIG hypervisor
>>> too, which should be able to spot things like this.
>>>
>>> This is a regression vs 4.21, so does need including.
>>
>> Aiui it's a regression vs 4.20, i.e. will want backporting to 4.21.
>>
>>> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, although...
>>
>> Thanks.
>>
>>>> --- a/xen/include/xsm/xsm.h
>>>> +++ b/xen/include/xsm/xsm.h
>>>> @@ -61,8 +61,10 @@ struct xsm_ops {
>>>>   #endif
>>>>       int (*set_target)(struct domain *d, struct domain *e);
>>>>       int (*domctl)(struct domain *d, struct xen_domctl *op);
>>>> +#ifdef CONFIG_SYSCTL
>>>>       int (*sysctl)(int cmd);
>>>>       int (*readconsole)(uint32_t clear);
>>>> +#endif
>>>
>>> ... this is now the 3rd CONFIG_SYSCTL in xsm_ops.
>>>
>>> I know it will grow the diff, but can we see about collecting them into
>>> a single region, and in dummy_ops too?  It will shrink the overall
>>> result, and the order of pointers in this ops structure is uninteresting.
>>
>> I have a far more consolidating patch in the works, which is how I actually
>> noticed the issue. I'd prefer to keep things as simple as possible here.
> 
> By the way, I was going back through this and notices that they are not 
> ifdef out in xsm/dummy.h. Are we relying on them being inlines to ensure 
> that they do not result in dead code?

I think so. Maybe it's unhelpful that we have

#define XSM_INLINE __maybe_unused

and we may instead better want explicit #ifdef wherever necessary.

Jan