Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 16 Feb 2021 17:51:34 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     James Bottomley <jejb@linux.ibm.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Mike Rapoport <rppt@kernel.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christopher Lameter <cl@linux.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Elena Reshetova <elena.reshetova@intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Roman Gushchin <guro@fb.com>,
        Shakeel Butt <shakeelb@google.com>,
        Shuah Khan <shuah@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
        linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org,
        x86@kernel.org, Hagen Paul Pfeifer <hagen@jauu.net>,
        Palmer Dabbelt <palmerdabbelt@google.com>
Subject: Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to
 create "secret" memory areas
Message-ID: <YCv4FhseXJ8cZ62/@dhcp22.suse.cz>
References: <20210214091954.GM242749@kernel.org>
 <052DACE9-986B-424C-AF8E-D6A4277DE635@redhat.com>
 <244f86cba227fa49ca30cd595c4e5538fe2f7c2b.camel@linux.ibm.com>
 <YCo7TqUnBdgJGkwN@dhcp22.suse.cz>
 <be1d821d3f0aec24ad13ca7126b4359822212eb0.camel@linux.ibm.com>
 <YCrJjYmr7A2nO6lA@dhcp22.suse.cz>
 <12c3890b233c8ec8e3967352001a7b72a8e0bfd0.camel@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <12c3890b233c8ec8e3967352001a7b72a8e0bfd0.camel@linux.ibm.com>
Precedence: bulk

On Tue 16-02-21 08:25:39, James Bottomley wrote:
> On Mon, 2021-02-15 at 20:20 +0100, Michal Hocko wrote:
> [...]
> > > >   What kind of flags are we talking about and why would that be a
> > > > problem with memfd_create interface? Could you be more specific
> > > > please?
> > > 
> > > You mean what were the ioctl flags in the patch series linked
> > > above? They were SECRETMEM_EXCLUSIVE and SECRETMEM_UNCACHED in
> > > patch 3/5. 
> > 
> > OK I see. How many potential modes are we talking about? A few or
> > potentially many?
>  
> Well I initially thought there were two (uncached or not) until you
> came up with the migratable or non-migratable, which affects the
> security properties.  But now there's also potential for hardware
> backing, like mktme,  described by flags as well.

I do not remember details about mktme but from what I still recall it
had keys associated with direct maps. Is the key management something
that fits into flags management?

> I suppose you could
> also use RDT to restrict which cache the data goes into: say L1 but not
> L2 on to lessen the impact of fully uncached (although the big thrust
> of uncached was to blunt hyperthread side channels).  So there is
> potential for quite a large expansion even though I'd be willing to bet
> that a lot of the modes people have thought about turn out not to be
> very effective in the field.

Are those very HW specific features really viable through a generic
syscall? Don't get me wrong but I find it much more likely somebody will
want a hugetlb (pretty HW independent) without a direct map than a very
close to the HW caching mode soon.

But thanks for the clarification anyway.
-- 
Michal Hocko
SUSE Labs