LKML Archive on
 help / color / Atom feed
From: Mike Rapoport <>
Cc: Alan Cox <>,
	Andrew Morton <>,
	Andy Lutomirski <>,
	Christopher Lameter <>,
	Dave Hansen <>,
	Idan Yaniv <>,
	James Bottomley <>,
	"Kirill A. Shutemov" <>,
	Matthew Wilcox <>,
	Peter Zijlstra <>,
	"Reshetova, Elena" <>,
	Thomas Gleixner <>,
	Tycho Andersen <>,,,
	Mike Rapoport <>
Subject: [RFC PATCH v2 0/5] mm: extend memfd with ability to create "secret" memory areas
Date: Mon,  6 Jul 2020 20:20:46 +0300
Message-ID: <> (raw)

From: Mike Rapoport <>


This is a second version of "secret" mappings implementation backed by a
file descriptor. 

The file descriptor is created using memfd_create() syscall with a new
MFD_SECRET flag. The file descriptor should be configured using ioctl() to
define the desired protection and then mmap() of the fd will create a
"secret" memory mapping. The pages in that mapping will be marked as not
present in the direct map and will have desired protection bits set in the
user page table. For instance, current implementation allows uncached

Hiding secret memory mappings behind an anonymous file allows (ab)use of
the page cache for tracking pages allocated for the "secret" mappings as
well as using address_space_operations for e.g. page migration callbacks.

The anonymous file may be also used implicitly, like hugetlb files, to
implement mmap(MAP_SECRET) and use the secret memory areas with "native" mm

As the fragmentation of the direct map was one of the major concerns raised
during the previous postings, I've added an amortizing cache of PMD-size
pages to each file descriptor and an ability to reserve large chunks of the
physical memory at boot time and then use this memory as an allocation pool
for the secret memory areas.

In addition, I've tried to find some numbers that show the benefit of using
larger pages in the direct map, but I couldn't find anything so I've run a
couple of benchmarks from phoronix-test-suite on my laptop (i7-8650U with
32G RAM).

I've tested three variants: the default with 28G of the physical memory
covered with 1G pages, then I disabled 1G pages using "nogbpages" in the
kernel command line and at last I've forced the entire direct map to use 4K
pages using a simple patch to arch/x86/mm/init.c.
I've made runs of the benchmarks with SSD and tmpfs.

Surprisingly, the results does not show huge advantage for large pages. For
instance, here the results for kernel build with 'make -j8', in seconds:

                        |  1G    |  2M    |  4K
ssd, mitigations=on	| 308.75 | 317.37 | 314.9 
ssd, mitigations=off	| 305.25 | 295.32 | 304.92 
ram, mitigations=on	| 301.58 | 322.49 | 306.54 
ram, mitigations=off	| 299.32 | 288.44 | 310.65

All the results I have are available at [1].
If anybody is interested in plain text, please let me know.


Mike Rapoport (5):
  mm: make HPAGE_PxD_{SHIFT,MASK,SIZE} always available
  mmap: make mlock_future_check() global
  mm: extend memfd with ability to create "secret" memory areas
  mm: secretmem: use PMD-size pages to amortize direct map fragmentation
  mm: secretmem: add ability to reserve memory at boot

 include/linux/huge_mm.h    |  10 +-
 include/linux/memfd.h      |   9 +
 include/uapi/linux/magic.h |   1 +
 include/uapi/linux/memfd.h |   6 +
 mm/Kconfig                 |   3 +
 mm/Makefile                |   1 +
 mm/internal.h              |   3 +
 mm/memfd.c                 |  10 +-
 mm/mmap.c                  |   5 +-
 mm/secretmem.c             | 445 +++++++++++++++++++++++++++++++++++++
 10 files changed, 480 insertions(+), 13 deletions(-)
 create mode 100644 mm/secretmem.c

base-commit: 7c30b859a947535f2213277e827d7ac7dcff9c84

             reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-06 17:20 Mike Rapoport [this message]
2020-07-06 17:20 ` [RFC PATCH v2 1/5] mm: make HPAGE_PxD_{SHIFT,MASK,SIZE} always available Mike Rapoport
2020-07-07  5:07   ` Hugh Dickins
2020-07-07  6:47     ` Mike Rapoport
2020-07-10 16:40     ` Andrea Arcangeli
2020-07-10 16:57       ` Matthew Wilcox
2020-07-10 17:08         ` Andrea Arcangeli
2020-07-10 17:12         ` Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 2/5] mmap: make mlock_future_check() global Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 3/5] mm: extend memfd with ability to create "secret" memory areas Mike Rapoport
2020-07-13 10:58   ` Kirill A. Shutemov
2020-07-13 15:31     ` Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 4/5] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2020-07-13 11:05   ` Kirill A. Shutemov
2020-07-13 15:32     ` Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 5/5] mm: secretmem: add ability to reserve memory at boot Mike Rapoport
2020-07-17  8:36 ` [RFC PATCH v2 0/5] mm: extend memfd with ability to create "secret" memory areas Pavel Machek
2020-07-17 14:43   ` James Bottomley

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on

Archives are clonable:
	git clone --mirror lkml/git/0.git
	git clone --mirror lkml/git/1.git
	git clone --mirror lkml/git/2.git
	git clone --mirror lkml/git/3.git
	git clone --mirror lkml/git/4.git
	git clone --mirror lkml/git/5.git
	git clone --mirror lkml/git/6.git
	git clone --mirror lkml/git/7.git
	git clone --mirror lkml/git/8.git
	git clone --mirror lkml/git/9.git
	git clone --mirror lkml/git/10.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ \
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone