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Date: Tue, 2 Feb 2021 15:34:29 +0100
From: David Hildenbrand <david@...hat.com>
To: Michal Hocko <mhocko@...e.com>
Cc: Mike Rapoport <rppt@...nel.org>,
James Bottomley <jejb@...ux.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
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Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
Catalin Marinas <catalin.marinas@....com>,
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Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Elena Reshetova <elena.reshetova@...el.com>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
"Kirill A. Shutemov" <kirill@...temov.name>,
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Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize
direct map fragmentation
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
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