Re: [PATCH v6 12/16] xen: implement new foreign copy hypercall

[Jan Beulich <jbeulich@xxxxxxxx>]

Daniel,

On 19.06.2026 15:04, Frediano Ziglio wrote:
> @@ -1545,6 +1545,139 @@ static int acquire_resource(
>      return rc;
>  }
>  
> +/*
> + * The "noinline" qualifier avoids the compiler to create a large function
> + * consuming quite a lot of stack.
> + */
> +static int noinline mem_foreigncopy(
> +    XEN_GUEST_HANDLE_PARAM(xen_foreigncopy_t) arg)
> +{
> +    struct domain *d, *const currd = current->domain;
> +    xen_foreigncopy_t copy;
> +    int rc, direction;
> +
> +    if ( copy_from_guest(&copy, arg, 1) )
> +        return -EFAULT;
> +
> +    if ( copy.flags & ~XENMEM_foreigncopy_direction )
> +        return -EINVAL;
> +
> +    direction = copy.flags & XENMEM_foreigncopy_direction;
> +
> +    rc = rcu_lock_remote_domain_by_id(copy.domid, &d);
> +    if ( rc )
> +        return rc;
> +
> +    if ( copy.nr_frames == 0 )
> +    {
> +        rcu_unlock_domain(d);
> +        return 0;
> +    }
> +
> +    /*
> +     * Check we are allowed to map and access these foreign pages.
> +     */
> +    rc = xsm_map_gmfn_foreign(XSM_TARGET, currd, d);
> +    if ( rc )
> +        goto out;

can you please clarify whether such a re-use of an existing predicate is
acceptable?

Jan