Re: [PATCH v7 3/3] xen/domain: introduce CONFIG_MAX_DOMID

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.05.2025 21:23, dmkhn@xxxxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx>
> 
> Embedded deployments of Xen do not need to have support for more than dozen of
> domains.
> 
> Introduce build-time configuration option to limit the number of domains 
> during
> run-time.

I fear I don't see the (sufficiently meaningful) gain of this. And I must have 
...

> Suggested-by: Julien Grall <julien@xxxxxxx>

... missed tis earlier suggestion, or else I would have asked the question 
already
there.

> --- a/xen/arch/arm/tee/ffa.c
> +++ b/xen/arch/arm/tee/ffa.c
> @@ -333,8 +333,9 @@ static int ffa_domain_init(struct domain *d)
>       */
>      BUILD_BUG_ON(DOMID_FIRST_RESERVED >= UINT16_MAX);
>      BUILD_BUG_ON((DOMID_MASK & BIT(15, U)) != 0);
> +    BUILD_BUG_ON(DOMID_FIRST_RESERVED < CONFIG_MAX_DOMID);

We want this check, yes, but in common code. It's entirely unrelated to Arm's 
TEE.

> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -576,4 +576,11 @@ config BUDDY_ALLOCATOR_SIZE
>         Amount of memory reserved for the buddy allocator to serve Xen heap,
>         working alongside the colored one.
>  
> +config MAX_DOMID
> +     int "Maximum number of non-system domains"

Hmm, without clarifying what a system domain is (is hwdom one? is a control
domain one), I fear this may be ambiguous to users.

Jan