Re: [PATCH v9 5/6] x86/boot: introduce domid field to struct boot_domain

[Jan Beulich <jbeulich@suse.com>]

On 15.11.2024 14:12, Daniel P. Smith wrote:
> Add a domid field to struct boot_domain to hold the assigned domain id for the
> domain. During initialization, ensure all instances of struct boot_domain have
> the invalid domid to ensure that the domid must be set either by convention or
> configuration.

I'm missing the "why" part here - after all ...

> --- a/xen/arch/x86/include/asm/bootdomain.h
> +++ b/xen/arch/x86/include/asm/bootdomain.h
> @@ -12,6 +12,8 @@ struct boot_module;
>  struct domain;
>  
>  struct boot_domain {
> +    domid_t domid;
> +
>      struct boot_module *kernel;
>      struct boot_module *ramdisk;
>  

... just out of context here there is struct domain *. I can only guess that
the domain ID is needed for the time until the domain pointer was actually
filled.

> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -339,6 +339,9 @@ static struct boot_info *__init multiboot_fill_boot_info(
>      /* Variable 'i' should be one entry past the last module. */
>      bi->mods[i].type = BOOTMOD_XEN;
>  
> +    for ( i = 0; i < MAX_NR_BOOTDOMS; i++ )
> +        bi->domains[i].domid = DOMID_INVALID;

Generally I think ARRAY_SIZE() is better to use for loop boundaries. Yet
then - why don't you statically initialize the array in xen_boot_info?

> @@ -977,7 +980,6 @@ static struct domain *__init create_dom0(struct boot_info *bi)
>      };
>      struct boot_domain *bd = &bi->domains[0];
>      struct domain *d;
> -    domid_t domid;
>  
>      if ( opt_dom0_pvh )
>      {
> @@ -993,15 +995,15 @@ static struct domain *__init create_dom0(struct boot_info *bi)
>          dom0_cfg.flags |= XEN_DOMCTL_CDF_iommu;
>  
>      /* Create initial domain.  Not d0 for pvshim. */
> -    domid = get_initial_domain_id();
> -    d = domain_create(domid, &dom0_cfg, pv_shim ? 0 : CDF_privileged);
> +    bd->domid = get_initial_domain_id();
> +    d = domain_create(bd->domid, &dom0_cfg, pv_shim ? 0 : CDF_privileged);
>      if ( IS_ERR(d) )
> -        panic("Error creating d%u: %ld\n", domid, PTR_ERR(d));
> +        panic("Error creating d%u: %ld\n", bd->domid, PTR_ERR(d));

As to the comment at the top - this change alone certainly doesn't clarify
the "why".

>      init_dom0_cpuid_policy(d);
>  
>      if ( alloc_dom0_vcpu0(d) == NULL )
> -        panic("Error creating d%uv0\n", domid);
> +        panic("Error creating d%uv0\n", bd->domid);

Imo this would better use d->domain_id. And while touching it, %u would also
want swapping for %d.

Jan