On 06.09.21 13:23, Jan Beulich wrote:
> On 06.09.2021 13:18, Andrew Cooper wrote:
>> On 06/09/2021 12:14, Andrew Cooper wrote:
>>> On 06/09/2021 12:00, Juergen Gross wrote:
>>>> In case a domain is created with a cpupool other than Pool-0 specified
>>>> it will be moved to that cpupool before any vcpus are allocated.
>>>>
>>>> This will lead to a NULL pointer dereference in sched_move_domain().
>>>>
>>>> Fix that by tolerating vcpus not being allocated yet.
>>>>
>>>> Fixes: 70fadc41635b9b6 ("xen/cpupool: support moving domain between cpupools with different granularity")
>>>> Reported-by: Bertrand Marquis <bertrand.marquis@arm.com>
>>>> Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
>>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>>> ---
>>>>   xen/common/sched/core.c | 4 ++++
>>>>   1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
>>>> index 8d178baf3d..79c9100680 100644
>>>> --- a/xen/common/sched/core.c
>>>> +++ b/xen/common/sched/core.c
>>>> @@ -671,6 +671,10 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
>>>>   
>>>>       for ( unit_idx = 0; unit_idx < n_units; unit_idx++ )
>>>>       {
>>>> +        /* Special case for move at domain creation time. */
>>>> +        if ( !d->vcpu[unit_idx * gran] )
>>>> +            break;
>>>> +
>>>>           unit = sched_alloc_unit_mem();
>>>>           if ( unit )
>>>>           {
>>> I think the logic would be clearer if you wrap the entire for loop in if
>>> ( d->max_vcpus ).
>>
>> And of course, this is wrong.  Turns out the domain_has_vcpus()
>> predicate still hasn't been committed, but d->vcpu[0] is the correct
>> internal.
> 
> Which in turn might want to be done by setting n_units to zero when
> d->vcpus[0] is NULL?

Yes, this would be possible.

OTOH my variant is more robust in case not all vcpus are allocated,
but I guess this will explode somewhere else anyway.

In case I don't get any other comment today I'll change the patch to set
n_units to 0 if d->vcpus[0] is NULL.


Juergen