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Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create
From: |
Kirill A. Shutemov |
Subject: |
Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory |
Date: |
Thu, 3 Nov 2022 19:30:12 +0300 |
On Wed, Nov 02, 2022 at 05:07:00PM -0500, Michael Roth wrote:
> On Thu, Nov 03, 2022 at 12:14:04AM +0300, Kirill A. Shutemov wrote:
> > On Mon, Oct 31, 2022 at 12:47:38PM -0500, Michael Roth wrote:
> > >
> > > In v8 there was some discussion about potentially passing the page/folio
> > > and order as part of the invalidation callback, I ended up needing
> > > something similar for SEV-SNP, and think it might make sense for other
> > > platforms. This main reasoning is:
> > >
> > > 1) restoring kernel directmap:
> > >
> > > Currently SNP (and I believe TDX) need to either split or remove
> > > kernel
> > > direct mappings for restricted PFNs, since there is no guarantee that
> > > other PFNs within a 2MB range won't be used for non-restricted
> > > (which will cause an RMP #PF in the case of SNP since the 2MB
> > > mapping overlaps with guest-owned pages)
> >
> > That's news to me. Where the restriction for SNP comes from?
>
> Sorry, missed your first question.
>
> For SNP at least, the restriction is documented in APM Volume 2, Section
> 15.36.10, First row of Table 15-36 (preceeding paragraph has more
> context). I forgot to mention this is only pertaining to writes by the
> host to 2MB pages that contain guest-owned subpages, for reads it's
> not an issue, but I think the implementation requirements end up being
> the same either way:
>
> https://www.amd.com/system/files/TechDocs/24593.pdf
Looks like you wanted restricted memfd to be backed by secretmem rather
then normal memfd. It would help preserve directmap.
--
Kiryl Shutsemau / Kirill A. Shutemov
- Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory, (continued)
Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory, Vlastimil Babka, 2022/11/14
Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory, Kirill A. Shutemov, 2022/11/02
Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory, Michael Roth, 2022/11/28
Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory, Michael Roth, 2022/11/28