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Date: Tue, 2 Feb 2021 15:26:20 +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>,
Matthew Wilcox <willy@...radead.org>,
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Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
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x86@...nel.org, Hagen Paul Pfeifer <hagen@...u.net>,
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 15:22, 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.
As I mentioned, we would have to temporarily map in order to copy.
Mapping it somewhere else (like kmap), outside of the direct map might
reduce possible attacks.
--
Thanks,
David / dhildenb
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