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Subject: Re: [RFC PATCH] mm: extend memfd with ability to create "secret"
 memory areas
To:     Mike Rapoport <rppt@kernel.org>, linux-kernel@vger.kernel.org
Cc:     Alan Cox <alan@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Christopher Lameter <cl@linux.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        James Bottomley <jejb@linux.ibm.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Reshetova, Elena" <elena.reshetova@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tycho Andersen <tycho@tycho.ws>, linux-api@vger.kernel.org,
        linux-mm@kvack.org
References: <20200130162340.GA14232@rapoport-lnx>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <df5a888b-1a11-e806-741d-94684b22c966@intel.com>
Date:   Thu, 6 Feb 2020 10:51:13 -0800
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Sender: linux-kernel-owner@vger.kernel.org
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On 1/30/20 8:23 AM, Mike Rapoport wrote:
>  include/linux/memfd.h      |   9 ++
>  include/uapi/linux/magic.h |   1 +
>  include/uapi/linux/memfd.h |   6 +
>  mm/Kconfig                 |   4 +
>  mm/Makefile                |   1 +
>  mm/memfd.c                 |  10 +-
>  mm/secretmem.c             | 244 +++++++++++++++++++++++++++++++++++++
>  7 files changed, 273 insertions(+), 2 deletions(-)

It seems pretty self-contained and relatively harmless.

But, how much work is it going to be to tell the rest of the kernel that
page_to_virt() doesn't work any more?  Do we need to make kmap() work on
these?

I guess fixing vm_normal_page() would fix a lot of that.

In general, my concern about creating little self-contained memory types
is that they will get popular and folks will start wanting more features
from them.  For instance, what if I want NUMA affinity, migration, or
large page mappings that are secret?

Can these pages work as guest memory?

Who would the first users of this thing be?