linux/Documentation/admin-guide/sysctl, branch v5.12

mm/vmscan: restore zone_reclaim_mode ABI

2021-02-24T21:38:34Z

I went to go add a new RECLAIM_* mode for the zone_reclaim_mode sysctl. Like a good kernel developer, I also went to go update the documentation. I noticed that the bits in the documentation didn't match the bits in the #defines. The VM never explicitly checks the RECLAIM_ZONE bit. The bit is, however implicitly checked when checking 'node_reclaim_mode==0'. The RECLAIM_ZONE #define was removed in a cleanup. That, by itself is fine. But, when the bit was removed (bit 0) the _other_ bit locations also got changed. That's not OK because the bit values are documented to mean one specific thing. Users surely do not expect the meaning to change from kernel to kernel. The end result is that if someone had a script that did: sysctl vm.zone_reclaim_mode=1 it would have gone from enabling node reclaim for clean unmapped pages to writing out pages during node reclaim after the commit in question. That's not great. Put the bits back the way they were and add a comment so something like this is a bit harder to do again. Update the documentation to make it clear that the first bit is ignored. Link: https://lkml.kernel.org/r/20210219172555.FF0CDF23@viggo.jf.intel.com Signed-off-by: Dave Hansen Fixes: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") Reviewed-by: Ben Widawsky Reviewed-by: Oscar Salvador Acked-by: David Rientjes Acked-by: Christoph Lameter Cc: Alex Shi Cc: Daniel Wagner Cc: "Tobin C. Harding" Cc: Christoph Lameter Cc: Andrew Morton Cc: Huang Ying Cc: Dan Williams Cc: Qian Cai Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Update Documentation/admin-guide/sysctl/fs.rst

2021-01-28T22:45:10Z

max_user_watches for epoll should say 1/25, rather than 1/32 Signed-off-by: Eric Curtin Link: https://lore.kernel.org/r/20210120132648.19046-1-ericcurtin17@gmail.com Signed-off-by: Jonathan Corbet

Merge tag 'docs-5.11-2' of git://git.lwn.net/linux

2020-12-24T22:20:33Z

Pull documentation fixes from Jonathan Corbet: "A small set of late-arriving, small documentation fixes" * tag 'docs-5.11-2' of git://git.lwn.net/linux: docs: admin-guide: Fix default value of max_map_count in sysctl/vm.rst Documentation/submitting-patches: Document the SoB chain Documentation: process: Correct numbering docs: submitting-patches: Trivial - fix grammatical error

docs: admin-guide: Fix default value of max_map_count in sysctl/vm.rst

2020-12-21T16:59:07Z

Since the default value of sysctl_max_map_count is defined as DEFAULT_MAX_MAP_COUNT from mm/util.c int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT; DEFAULT_MAX_MAP_COUNT is defined as 65530 (65535-5) in include/linux/mm.h #define MAPCOUNT_ELF_CORE_MARGIN (5) #define DEFAULT_MAX_MAP_COUNT (USHRT_MAX - MAPCOUNT_ELF_CORE_MARGIN) Signed-off-by: Fengfei Xi Link: https://lore.kernel.org/r/20201210082134.36957-1-xi.fengfei@h3c.com Signed-off-by: Jonathan Corbet

Merge branch 'akpm' (patches from Andrew)

2020-12-15T20:53:37Z

Merge misc updates from Andrew Morton: - a few random little subsystems - almost all of the MM patches which are staged ahead of linux-next material. I'll trickle to post-linux-next work in as the dependents get merged up. Subsystems affected by this patch series: kthread, kbuild, ide, ntfs, ocfs2, arch, and mm (slab-generic, slab, slub, dax, debug, pagecache, gup, swap, shmem, memcg, pagemap, mremap, hmm, vmalloc, documentation, kasan, pagealloc, memory-failure, hugetlb, vmscan, z3fold, compaction, oom-kill, migration, cma, page-poison, userfaultfd, zswap, zsmalloc, uaccess, zram, and cleanups). * emailed patches from Andrew Morton : (200 commits) mm: cleanup kstrto*() usage mm: fix fall-through warnings for Clang mm: slub: convert sysfs sprintf family to sysfs_emit/sysfs_emit_at mm: shmem: convert shmem_enabled_show to use sysfs_emit_at mm:backing-dev: use sysfs_emit in macro defining functions mm: huge_memory: convert remaining use of sprintf to sysfs_emit and neatening mm: use sysfs_emit for struct kobject * uses mm: fix kernel-doc markups zram: break the strict dependency from lzo zram: add stat to gather incompressible pages since zram set up zram: support page writeback mm/process_vm_access: remove redundant initialization of iov_r mm/zsmalloc.c: rework the list_add code in insert_zspage() mm/zswap: move to use crypto_acomp API for hardware acceleration mm/zswap: fix passing zero to 'PTR_ERR' warning mm/zswap: make struct kernel_param_ops definitions const userfaultfd/selftests: hint the test runner on required privilege userfaultfd/selftests: fix retval check for userfaultfd_open() userfaultfd/selftests: always dump something in modes userfaultfd: selftests: make __{s,u}64 format specifiers portable ...

userfaultfd: add user-mode only option to unprivileged_userfaultfd sysctl knob

2020-12-15T20:13:46Z

With this change, when the knob is set to 0, it allows unprivileged users to call userfaultfd, like when it is set to 1, but with the restriction that page faults from only user-mode can be handled. In this mode, an unprivileged user (without SYS_CAP_PTRACE capability) must pass UFFD_USER_MODE_ONLY to userfaultd or the API will fail with EPERM. This enables administrators to reduce the likelihood that an attacker with access to userfaultfd can delay faulting kernel code to widen timing windows for other exploits. The default value of this knob is changed to 0. This is required for correct functioning of pipe mutex. However, this will fail postcopy live migration, which will be unnoticeable to the VM guests. To avoid this, set 'vm.userfault = 1' in /sys/sysctl.conf. The main reason this change is desirable as in the short term is that the Android userland will behave as with the sysctl set to zero. So without this commit, any Linux binary using userfaultfd to manage its memory would behave differently if run within the Android userland. For more details, refer to Andrea's reply [1]. [1] https://lore.kernel.org/lkml/20200904033438.GI9411@redhat.com/ Link: https://lkml.kernel.org/r/20201120030411.2690816-3-lokeshgidra@google.com Signed-off-by: Lokesh Gidra Reviewed-by: Andrea Arcangeli Cc: Kees Cook Cc: Jonathan Corbet Cc: Peter Xu Cc: Sebastian Andrzej Siewior Cc: Alexander Viro Cc: Stephen Smalley Cc: Eric Biggers Cc: Daniel Colascione Cc: "Joel Fernandes (Google)" Cc: Kalesh Singh Cc: Suren Baghdasaryan Cc: Jeff Vander Stoep Cc: Cc: Mike Rapoport Cc: Shaohua Li Cc: Jerome Glisse Cc: Mauro Carvalho Chehab Cc: Johannes Weiner Cc: Mel Gorman Cc: Nitin Gupta Cc: Vlastimil Babka Cc: Iurii Zaikin Cc: Luis Chamberlain Cc: Daniel Colascione Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

docs: Update documentation to reflect what TAINT_CPU_OUT_OF_SPEC means

2020-12-08T17:53:58Z

Here's a patch updating the meaning of TAINT_CPU_OUT_OF_SPEC after Borislav introduced changes in a7e1f67ed29f and upcoming patches in tip. TAINT_CPU_OUT_OF_SPEC now means a bit more what it implies as the flag isn't set just because of a CPU misconfiguration or mismatch. Historically it was for SMP kernel oops on an officially SMP incapable processor but now it also covers CPUs whose MSRs have been incorrectly poked at from userspace, drivers being used on non supported architectures, broken firmware, mismatched CPUs, ... Update documentation and script to reflect that. Signed-off-by: Mathieu Chouquet-Stringer Link: https://lore.kernel.org/r/20201202153244.709752-1-me@mathieu.digital Signed-off-by: Jonathan Corbet

Documentation: fix multiple typos found in the admin-guide subdirectory

2020-12-08T17:27:56Z

Fix thirty five typos in dm-integrity.rst, dm-raid.rst, dm-zoned.rst, verity.rst, writecache.rst, tsx_async_abort.rst, md.rst, bttv.rst, dvb_references.rst, frontend-cardlist.rst, gspca-cardlist.rst, ipu3.rst, remote-controller.rst, mm/index.rst, numaperf.rst, userfaultfd.rst, module-signing.rst, imx-ddr.rst, intel-speed-select.rst, intel_pstate.rst, ramoops.rst, abi.rst, kernel.rst, vm.rst Signed-off-by: Andrew Klychkov Link: https://lore.kernel.org/r/20201204072848.GA49895@spblnx124.lan Signed-off-by: Jonathan Corbet

docs: clean up sysctl/kernel: titles, version

2020-12-08T17:22:21Z

This cleans up a few titles with extra colons, and removes the reference to kernel 2.2. The docs don't yet cover *all* of 5.10 or 5.11, but I think they're close enough. Most entries are documented, and have been checked against current kernels. Signed-off-by: Stephen Kitt Link: https://lore.kernel.org/r/20201208074922.30359-1-steve@sk2.org Signed-off-by: Jonathan Corbet

docs: admin-guide: net.rst: add a missing blank line

2020-10-28T17:26:10Z

There's a missing blank line after a literal block, which causes this warning: Documentation/admin-guide/sysctl/net.rst:303: WARNING: Literal block ends without a blank line; unexpected unindent. Signed-off-by: Mauro Carvalho Chehab Link: https://lore.kernel.org/r/b2545be4a4c71269d10278b5990c3e06c4b65f84.1603791716.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet