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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

> @@ -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.

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.

> + * Direct-mapped domains (autotranslated domains with memory allocated
> + * contiguously and mapped 1:1 so that GFN == MFN) are always using the
> + * host memory layout to avoid address clashes.
> + *
> + * The hardware domain will use the host layout (regardless of
> + * direct-mapped) because some OS may rely on a specific address ranges
> + * for the devices. PV Dom0, like any other PV guests, has
> + * domain_use_host_layout() returning False.
> + */
> +bool domain_use_host_layout(struct domain *d);

Like about any other predicate, its parameter wants to be pointer-to-
const. (And I really shouldn't need to repeat this to you every other
time.)

Jan