Re: [PATCH v2 07/11] xen: move domain_use_host_layout() to common code

[Jan Beulich <jbeulich@xxxxxxxx>]

On 31.03.2026 17:20, Oleksii Kurochko wrote:
> On 3/30/26 5:13 PM, Jan Beulich wrote:
>> On 23.03.2026 17:29, Oleksii Kurochko wrote:
>>> domain_use_host_layout() is not really architecture-specific, so move it
>>> from the Arm header to the common header xen/domain.h and provide a common
>>> implementation in xen/common/domain.c. domain_use_host_layout() potentially
>>> is needed for x86 [1].
>>
>> No matter that this may indeed be true, ...
>>
>>> Turn the macro into a function to avoid header dependency issues.
>>
>> ... this introduces unreachable code on x86, i.e. a Misra rule 2.1 violation.
> 
> Do we have some deviation tag for such cases when the code temporary 
> isn't used?

I'm sorry, but it'll take me about as long as you to find out. I wonder
about "temporary" though: Do you have a clear understanding as to when
that will change?

>>> @@ -2544,6 +2544,12 @@ void thaw_domains(void)
>>>   
>>>   #endif /* CONFIG_SYSTEM_SUSPEND */
>>>   
>>> +bool domain_use_host_layout(struct domain *d)
>>> +{
>>> +    return is_domain_direct_mapped(d) ||
>>> +           (paging_mode_translate(d) && is_hardware_domain(d));
>>> +}
>>
>> The placement of paging_mode_translate() doesn't match ...
>>
>>> --- a/xen/include/xen/domain.h
>>> +++ b/xen/include/xen/domain.h
>>> @@ -62,6 +62,22 @@ void domid_free(domid_t domid);
>>>   #define is_domain_direct_mapped(d) ((d)->cdf & CDF_directmap)
>>>   #define is_domain_using_staticmem(d) ((d)->cdf & CDF_staticmem)
>>>   
>>> +/*
>>> + * Is the auto-translated domain using the host memory layout?
>>> + *
>>> + * domain_use_host_layout() is always False for PV guests.
>>
>> ... the description of the function.
> 
> But why the placement should be different?

If you focus on auto-translated, then imo paging_mode_translate()
better would guard everything.

> is_domain_direct_mapped() is false for PV guests (and for other guest 
> types on x86).
> 
> So if domain_use_host_layout() is fully depends on 
> paging_mode_translate(d) && is_hardware_domain(d) and for which 
> paging_mode_translate() is false if it is PV guest.
> Thereby domain_use_host_layout() is false too.
> 
>>
>> Further, the first sentence above suggests the caller has to check
>> paging_mode_translate() before calling, which as per the implementation
>> clearly isn't the intention.
> 
> Sorry, I don't follow you here.

By starting the comment with "Is the auto-translated domain using", you
imply the caller checked for that aspect already. At least the way I
read it.

Jan