[xen staging] xen/arm: Fail domain construction if a secondary vCPU cannot be created

[patchbot@xxxxxxx]

commit e3aa330017c533cc312ee4751b8387d988682efc
Author:     Michal Orzel <michal.orzel@xxxxxxx>
AuthorDate: Thu Jul 9 08:36:43 2026 +0200
Commit:     Michal Orzel <michal.orzel@xxxxxxx>
CommitDate: Mon Jul 13 09:01:26 2026 +0200

    xen/arm: Fail domain construction if a secondary vCPU cannot be created
    
    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>
    Reviewed-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
    Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
    Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 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 550617f152..72d5316180 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) )
--
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