Re: [PATCH v3 1/2][4.15] VMX: delay p2m insertion of APIC access page

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.02.2021 12:25, Ian Jackson wrote:
> Jan Beulich writes ("[PATCH v3 1/2][4.15] VMX: delay p2m insertion of APIC 
> access page"):
>> Inserting the mapping at domain creation time leads to a memory leak
>> when the creation fails later on and the domain uses separate CPU and
>> IOMMU page tables - the latter requires intermediate page tables to be
>> allocated, but there's no freeing of them at present in this case. Since
>> we don't need the p2m insertion to happen this early, avoid the problem
>> altogether by deferring it until the last possible point.
> 
> Thanks.
> 
>>   This comes at
>> the price of not being able to handle an error other than by crashing
>> the domain.
> 
> How worried should I be about this ?

Not overly much I would say. The difference is between a failure
(-ENOMEM) during domain creation vs the domain getting crashed
before it gets first scheduled. This is certainly less friendly
to the user, but lack of memory shouldn't typically happen when
creating domains. Plus the memory talked about here is such that
gets provided explicitly to the domain (the p2m pool), rather
than a system wide pool.

Jan