Re: [for-4.22][PATCH v2] xen/arm: Fail domain construction if a secondary vCPU cannot be created

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 7/9/26 8:36 AM, Michal Orzel wrote:
> construct_domain() creates the secondary vCPUs in a loop, but on a
> vcpu_create() failure it only prints a message and breaks out of the
> loop returning success. As a result the domain can be partially
> constructed with fewer vCPUs than d->max_vcpus. This causes two contract
> violations:
>   - Xen-Guest: domain's FDT is generated before vCPU creation - Xen exposes
>     incorrect information (e.g. two vCPUs listed in a device tree while only
>     one is actually created),
>   - User-Xen: unlike x86, on Arm port we try to bail out as soon as
>     possible on unsatisfied user requests (e.g. user requested two vCPUs
>     for a domain but it was created with only one).
>
> Return an error instead of breaking out of the loop. Both callers
> (construct_domU() and construct_hwdom()) already propagate a negative
> return value and fail domain construction.
>
> Fixes: 6b0e8e43348a ("xen/arm: allocate secondaries dom0 vcpus")
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> ---
> Changes in v2:
>   - return ENOMEM as allocation failure is most frequent cause of failure
>   - update commit msg to focus on unmet contracts
> ---
>   xen/arch/arm/domain_build.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 550617f152bb..72d531618045 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -1847,7 +1847,7 @@ int __init construct_domain(struct domain *d, struct 
> kernel_info *kinfo)
>           if ( vcpu_create(d, i) == NULL )
>           {
>               printk("Failed to allocate d%dv%d\n", d->domain_id, i);
> -            break;
> +            return -ENOMEM;
>           }
>   
>           if ( is_64bit_domain(d) )
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

Thanks.

~ Oleksii