Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation

David Hildenbrand
2021-02-02T14:35:05Z

On 02.02.21 15:32, Michal Hocko wrote:
> On Tue 02-02-21 15:26:20, David Hildenbrand wrote:
>> On 02.02.21 15:22, Michal Hocko wrote:
>>> On Tue 02-02-21 15:12:21, David Hildenbrand wrote:
>>> [...]
>>>> I think secretmem behaves much more like longterm GUP right now
>>>> ("unmigratable", "lifetime controlled by user space", "cannot go on
>>>> CMA/ZONE_MOVABLE"). I'd either want to reasonably well control/limit it or
>>>> make it behave more like mlocked pages.
>>>
>>> I thought I have already asked but I must have forgotten. Is there any
>>> actual reason why the memory is not movable? Timing attacks?
>>
>> I think the reason is simple: no direct map, no copying of memory.
>
> This is an implementation detail though and not something terribly hard
> to add on top later on. I was more worried there would be really
> fundamental reason why this is not possible. E.g. security implications.

I don't remember all the details. Let's see what Mike thinks regarding
migration (e.g., security concerns).

--
Thanks,

David / dhildenb