Re: [PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag

[David Hildenbrand]

On 07.02.22 19:51, Vlastimil Babka wrote:
> On 1/18/22 14:21, Chao Peng wrote:
>> Introduce a new memfd_create() flag indicating the content of the
>> created memfd is inaccessible from userspace. It does this by force
>> setting F_SEAL_INACCESSIBLE seal when the file is created. It also set
>> F_SEAL_SEAL to prevent future sealing, which means, it can not coexist
>> with MFD_ALLOW_SEALING.
>>
>> The pages backed by such memfd will be used as guest private memory in
>> confidential computing environments such as Intel TDX/AMD SEV. Since
>> page migration/swapping is not yet supported for such usages so these
>> pages are currently marked as UNMOVABLE and UNEVICTABLE which makes
>> them behave like long-term pinned pages.
> 
> Shouldn't the amount of such memory allocations be restricted? E.g. similar
> to secretmem_mmap() doing mlock_future_check().

I've raised this already in the past and Kirill wanted to look into it [1].

We'll most certainly need a way to limit/control the amount of
unswappable + unmovable ("worse than mlock" memory) a user/process can
consume via this mechanism.


[1]
https://lkml.kernel.org/r/20211122135933.arjxpl7wyskkwvwv@box.shutemov.name


-- 
Thanks,

David / dhildenb