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

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

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