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

[Oleksii Kurochko <oleksii.kurochko@gmail.com>]

On 4/1/26 7:58 AM, Jan Beulich wrote:
> On 31.03.2026 18:32, Oleksii Kurochko wrote:
>> On 3/31/26 5:53 PM, Jan Beulich wrote:
>>> 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.
>> Sure, I will take a look. I just thought that maybe you have a solution
>> already just in your head.
> Well, I do: Don't make this an out-of-line function.
> 
>>    I wonder
>>> about "temporary" though: Do you have a clear understanding as to when
>>> that will change?
>> No, I don't. As Stefano mentioned they will need this function one day.
>> Another option we could use ifndef x86 or ifdef DOM0_LESS and then when
>> someone will really need it on x86, this ifdef will be dropped. I don't
>> know if it is better solution.
>>
>> It seems like the best one solution will still make a try to make
>> declare this function as macro.
> Or an inline function. There's nothing ...
> 
>>>>>> @@ -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.
>> Then it make sense to do in the following way:
>>    bool domain_use_host_layout(struct domain *d)
>>    {
>> -    return is_domain_direct_mapped(d) ||
>> -           (paging_mode_translate(d) && is_hardware_domain(d));
>> +    return paging_mode_translate(d) &&
>> +           (is_domain_direct_mapped(d) || is_hardware_domain(d));
>>    }
> ... in here which clearly speaks against doing so. And yes, this is what I
> was asking for (with the function parameter also suitably constified).

I expect that with an inline function in xen/domain.h compiler will want 
have paging_mode_translate() be explicitly defined, so an inclusion of 
xen/paging.h will be needed, but likely I am wrong that it will be 
needed it the case of inline function.

~ Oleksii