Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas

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To: "rppt@xxxxxxxxxx" <rppt@xxxxxxxxxx>, "Hansen, Dave" <dave.hansen@xxxxxxxxx>
Subject: Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas
From: "Edgecombe, Rick P" <rick.p.edgecombe@xxxxxxxxx>
Date: Tue, 11 Feb 2020 19:52:47 +0000
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Cc: "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "peterz@xxxxxxxxxxxxx" <peterz@xxxxxxxxxxxxx>, "jejb@xxxxxxxxxxxxx" <jejb@xxxxxxxxxxxxx>, "alan@xxxxxxxxxxxxxxx" <alan@xxxxxxxxxxxxxxx>, "tglx@xxxxxxxxxxxxx" <tglx@xxxxxxxxxxxxx>, "dave.hansen@xxxxxxxxxxxxxxx" <dave.hansen@xxxxxxxxxxxxxxx>, "linux-api@xxxxxxxxxxxxxxx" <linux-api@xxxxxxxxxxxxxxx>, "willy@xxxxxxxxxxxxx" <willy@xxxxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, "cl@xxxxxxxxx" <cl@xxxxxxxxx>, "akpm@xxxxxxxxxxxxxxxxxxxx" <akpm@xxxxxxxxxxxxxxxxxxxx>, "Reshetova, Elena" <elena.reshetova@xxxxxxxxx>, "tycho@xxxxxxxx" <tycho@xxxxxxxx>, "luto@xxxxxxxxxx" <luto@xxxxxxxxxx>, "kirill@xxxxxxxxxxxxx" <kirill@xxxxxxxxxxxxx>
In-reply-to: <20200208173922.GA15879@hump>
References: <20200130162340.GA14232@rapoport-lnx> <df5a888b-1a11-e806-741d-94684b22c966@intel.com> <20200208173922.GA15879@hump>

On Sat, 2020-02-08 at 19:39 +0200, Mike Rapoport wrote:
> > Do we need to make kmap() work on these?
> 
> I don't think we need to make kmap() work on these. The idea is to prevent
> kernel from accessing such memory areas.

For the VM use case, KVM does kmap() guest memory when emulating page table
operations in some cases:
arch/x86/kvm/paging_tmpl.h:FNAME(cmpxchg_gpte).

References:
- [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas
  - From: Mike Rapoport
- Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas
  - From: Dave Hansen
- Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas
  - From: Mike Rapoport

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