Re: [PATCH for-4.19? v5 07/10] xen: Make the maximum number of altp2m views configurable for x86

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.06.2024 11:10, Petr Beneš wrote:
> On Mon, Jun 10, 2024 at 9:30 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 09.06.2024 01:06, Petr Beneš wrote:
>>> On Thu, Jun 6, 2024 at 9:24 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>>> @@ -122,7 +131,12 @@ int p2m_init_altp2m(struct domain *d)
>>>>>      struct p2m_domain *hostp2m = p2m_get_hostp2m(d);
>>>>>
>>>>>      mm_lock_init(&d->arch.altp2m_list_lock);
>>>>> -    for ( i = 0; i < MAX_ALTP2M; i++ )
>>>>> +    d->arch.altp2m_p2m = xzalloc_array(struct p2m_domain *, 
>>>>> d->nr_altp2m);
>>>>> +
>>>>> +    if ( !d->arch.altp2m_p2m )
>>>>> +        return -ENOMEM;
>>>>
>>>> This isn't really needed, is it? Both ...
>>>>
>>>>> +    for ( i = 0; i < d->nr_altp2m; i++ )
>>>>
>>>> ... this and ...
>>>>
>>>>>      {
>>>>>          d->arch.altp2m_p2m[i] = p2m = p2m_init_one(d);
>>>>>          if ( p2m == NULL )
>>>>> @@ -143,7 +157,10 @@ void p2m_teardown_altp2m(struct domain *d)
>>>>>      unsigned int i;
>>>>>      struct p2m_domain *p2m;
>>>>>
>>>>> -    for ( i = 0; i < MAX_ALTP2M; i++ )
>>>>> +    if ( !d->arch.altp2m_p2m )
>>>>> +        return;
>>
>> I'm sorry, the question was meant to be on this if() instead.
>>
>>>>> +    for ( i = 0; i < d->nr_altp2m; i++ )
>>>>>      {
>>>>>          if ( !d->arch.altp2m_p2m[i] )
>>>>>              continue;
>>>>> @@ -151,6 +168,8 @@ void p2m_teardown_altp2m(struct domain *d)
>>>>>          d->arch.altp2m_p2m[i] = NULL;
>>>>>          p2m_free_one(p2m);
>>>>>      }
>>>>> +
>>>>> +    XFREE(d->arch.altp2m_p2m);
>>>>>  }
>>>>
>>>> ... this ought to be fine without?
>>>
>>> Could you, please, elaborate? I honestly don't know what you mean here
>>> (by "this isn't needed").
>>
>> I hope the above correction is enough?
> 
> I'm sorry, but not really? I feel like I'm blind but I can't see
> anything I could remove without causing (or risking) crash.

The loop is going to do nothing when d->nr_altp2m == 0, and the XFREE() is
going to do nothing when d->arch.altp2m_p2m == NULL. Hence what does the
if() guard against? IOW what possible crashes are you seeing that I don't
see?

Jan