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

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Message-ID: <20200806111415.GL163101@linux.ibm.com>
Date:   Thu, 6 Aug 2020 14:14:15 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Mike Rapoport <rppt@...nel.org>, 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>,
        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 Thu, Aug 06, 2020 at 01:27:57PM +0300, Kirill A. Shutemov wrote:
> 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.

Makes sense.

> What am I missing?
>
> -- 
>  Kirill A. Shutemov

-- 
Sincerely yours,
Mike.