From: Michal Hocko <mhocko@suse.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: 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>,
David Hildenbrand <david@redhat.com>,
Elena Reshetova <elena.reshetova@intel.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
James Bottomley <jejb@linux.ibm.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Matthew Wilcox <willy@infradead.org>,
Mark Rutland <mark.rutland@arm.com>,
Mike Rapoport <rppt@linux.ibm.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,
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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 v16 06/11] mm: introduce memfd_secret system call to create "secret" memory areas
Date: Tue, 26 Jan 2021 10:49:03 +0100 [thread overview]
Message-ID: <20210126094903.GI827@dhcp22.suse.cz> (raw)
In-Reply-To: <20210126092011.GP6332@kernel.org>
On Tue 26-01-21 11:20:11, Mike Rapoport wrote:
> On Tue, Jan 26, 2021 at 10:00:13AM +0100, Michal Hocko wrote:
> > On Tue 26-01-21 10:33:11, Mike Rapoport wrote:
> > > On Tue, Jan 26, 2021 at 08:16:14AM +0100, Michal Hocko wrote:
> > > > On Mon 25-01-21 23:36:18, Mike Rapoport wrote:
> > > > > On Mon, Jan 25, 2021 at 06:01:22PM +0100, Michal Hocko wrote:
> > > > > > On Thu 21-01-21 14:27:18, Mike Rapoport wrote:
> > > > > > > From: Mike Rapoport <rppt@linux.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. The memory areas created by mmap() calls from this file descriptor
> > > > > > > will be unmapped from the kernel direct map and they will be only mapped in
> > > > > > > the page table of the owning mm.
> > > > > > >
> > > > > > > The secret memory remains accessible in the process context using uaccess
> > > > > > > primitives, but it is not accessible using direct/linear map addresses.
> > > > > > >
> > > > > > > Functions in the follow_page()/get_user_page() family will refuse to return
> > > > > > > a page that belongs to the secret memory area.
> > > > > > >
> > > > > > > A page that was a part of the secret memory area is cleared when it is
> > > > > > > freed.
> > > > > > >
> > > > > > > The following example demonstrates creation of a secret mapping (error
> > > > > > > handling is omitted):
> > > > > > >
> > > > > > > fd = memfd_secret(0);
> > > > > > > ftruncate(fd, MAP_SIZE);
> > > > > > > ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> > > > > >
> > > > > > I do not see any access control or permission model for this feature.
> > > > > > Is this feature generally safe to anybody?
> > > > >
> > > > > The mappings obey memlock limit. Besides, this feature should be enabled
> > > > > explicitly at boot with the kernel parameter that says what is the maximal
> > > > > memory size secretmem can consume.
> > > >
> > > > Why is such a model sufficient and future proof? I mean even when it has
> > > > to be enabled by an admin it is still all or nothing approach. Mlock
> > > > limit is not really useful because it is per mm rather than per user.
> > > >
> > > > Is there any reason why this is allowed for non-privileged processes?
> > > > Maybe this has been discussed in the past but is there any reason why
> > > > this cannot be done by a special device which will allow to provide at
> > > > least some permission policy?
> > >
> > > Why this should not be allowed for non-privileged processes? This behaves
> > > similarly to mlocked memory, so I don't see a reason why secretmem should
> > > have different permissions model.
> >
> > Because appart from the reclaim aspect it fragments the direct mapping
> > IIUC. That might have an impact on all others, right?
>
> It does fragment the direct map, but first it only splits 1G pages to 2M
> pages and as was discussed several times already it's not that clear which
> page size in the direct map is the best and this is very much workload
> dependent.
I do appreciate this has been discussed but this changelog is not
specific on any of that reasoning and I am pretty sure nobody will
remember details in few years in the future. Also some numbers would be
appropriate.
> These are the results of the benchmarks I've run with the default direct
> mapping covered with 1G pages, with disabled 1G pages using "nogbpages" in
> the kernel command line and with the entire direct map forced to use 4K
> pages using a simple patch to arch/x86/mm/init.c.
>
> https://docs.google.com/spreadsheets/d/1tdD-cu8e93vnfGsTFxZ5YdaEfs2E1GELlvWNOGkJV2U/edit?usp=sharing
A good start for the data I am asking above.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-01-26 11:30 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 12:27 [PATCH v16 00/11] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 01/11] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 02/11] mmap: make mlock_future_check() global Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 03/11] riscv/Kconfig: make direct map manipulation options depend on MMU Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 04/11] set_memory: allow set_direct_map_*_noflush() for multiple pages Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 05/11] set_memory: allow querying whether set_direct_map_*() is actually enabled Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 06/11] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-01-25 17:01 ` Michal Hocko
2021-01-25 21:36 ` Mike Rapoport
2021-01-26 7:16 ` Michal Hocko
2021-01-26 8:33 ` Mike Rapoport
2021-01-26 9:00 ` Michal Hocko
2021-01-26 9:20 ` Mike Rapoport
2021-01-26 9:49 ` Michal Hocko [this message]
2021-01-26 9:53 ` David Hildenbrand
2021-01-26 10:19 ` Michal Hocko
2021-01-26 9:20 ` Michal Hocko
2021-02-03 12:15 ` Michal Hocko
2021-02-04 11:34 ` Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2021-01-26 11:46 ` Michal Hocko
2021-01-26 11:56 ` David Hildenbrand
2021-01-26 12:08 ` Michal Hocko
2021-01-28 9:22 ` Mike Rapoport
2021-01-28 13:01 ` Michal Hocko
2021-01-28 13:28 ` Christoph Lameter
2021-01-28 13:49 ` Michal Hocko
2021-01-28 15:56 ` Christoph Lameter
2021-01-28 16:23 ` Michal Hocko
2021-01-28 15:28 ` James Bottomley
2021-01-29 7:03 ` Mike Rapoport
2021-01-28 21:05 ` James Bottomley
2021-01-29 8:23 ` Michal Hocko
2021-02-01 16:56 ` James Bottomley
2021-02-02 9:35 ` Michal Hocko
2021-02-02 12:48 ` Mike Rapoport
2021-02-02 13:14 ` David Hildenbrand
2021-02-02 13:32 ` Michal Hocko
2021-02-02 14:12 ` David Hildenbrand
2021-02-02 14:22 ` Michal Hocko
2021-02-02 14:26 ` David Hildenbrand
2021-02-02 14:32 ` Michal Hocko
2021-02-02 14:34 ` David Hildenbrand
2021-02-02 18:15 ` Mike Rapoport
2021-02-02 18:55 ` James Bottomley
2021-02-03 12:09 ` Michal Hocko
2021-02-04 11:31 ` Mike Rapoport
2021-02-02 13:27 ` Michal Hocko
2021-02-02 19:10 ` Mike Rapoport
2021-02-03 9:12 ` Michal Hocko
2021-02-04 9:58 ` Mike Rapoport
2021-02-04 13:02 ` Michal Hocko
2021-01-29 7:21 ` Mike Rapoport
[not found] ` <YBPMg/C5Sb78gFEB@dhcp22.suse.cz>
2021-02-02 14:42 ` David Hildenbrand
2021-01-21 12:27 ` [PATCH v16 08/11] secretmem: add memcg accounting Mike Rapoport
2021-01-25 16:17 ` Matthew Wilcox
2021-01-25 17:18 ` Shakeel Butt
2021-01-25 21:35 ` Mike Rapoport
2021-01-28 15:07 ` Shakeel Butt
2021-01-25 16:54 ` Michal Hocko
2021-01-25 21:38 ` Mike Rapoport
2021-01-26 7:31 ` Michal Hocko
2021-01-26 8:56 ` Mike Rapoport
2021-01-26 9:15 ` Michal Hocko
2021-01-26 14:48 ` Matthew Wilcox
2021-01-26 15:05 ` Michal Hocko
2021-01-27 18:42 ` Roman Gushchin
2021-01-28 7:58 ` Michal Hocko
2021-01-28 14:05 ` Shakeel Butt
2021-01-28 14:22 ` Michal Hocko
2021-01-28 14:57 ` Shakeel Butt
2021-01-21 12:27 ` [PATCH v16 09/11] PM: hibernate: disable when there are active secretmem users Mike Rapoport
2021-01-21 12:27 ` [PATCH v16 10/11] arch, mm: wire up memfd_secret system call where relevant Mike Rapoport
2021-01-25 18:18 ` Catalin Marinas
2021-01-21 12:27 ` [PATCH v16 11/11] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2021-01-21 22:18 ` [PATCH v16 00/11] mm: introduce memfd_secret system call to create "secret" memory areas Andrew Morton
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