linux-kernel - Re: [PATCH v3 3/6] mm: introduce memfd_secret system call to create "secret" memory areas

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Message-ID: <20200806102757.7vobcaewdukr2xdl@box>
Date:   Thu, 6 Aug 2020 13:27:57 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christopher Lameter <cl@...ux.com>,
        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>, Idan Yaniv <idan.yaniv@....com>,
        Ingo Molnar <mingo@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org
Subject: Re: [PATCH v3 3/6] mm: introduce memfd_secret system call to create
 "secret" memory areas

On Tue, Aug 04, 2020 at 12:50:32PM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> Introduce "memfd_secret" system call with the ability to create memory
> areas visible only in the context of the owning process and not mapped not
> only to other processes but in the kernel page tables as well.
> 
> The user will create a file descriptor using the memfd_secret() system call
> where flags supplied as a parameter to this system call will define the
> desired protection mode for the memory associated with that file
> descriptor. Currently there are two protection modes:
> 
> * exclusive - the memory area is unmapped from the kernel direct map and it
>               is present only in the page tables of the owning mm.
> * uncached  - the memory area is present only in the page tables of the
>               owning mm and it is mapped there as uncached.

I'm not sure why flag for exclusive mode is needed. It has to be default.
And if you want uncached on top of that set the flag.
What am I missing?

-- 
 Kirill A. Shutemov