linux-stable.git/Documentation/admin-guide, branch v5.8.7

ext4: limit the length of per-inode prealloc list

2020-09-03T09:29:37+00:00

[ Upstream commit 27bc446e2def38db3244a6eb4bb1d6312936610a ]

In the scenario of writing sparse files, the per-inode prealloc list may
be very long, resulting in high overhead for ext4_mb_use_preallocated().
To circumvent this problem, we limit the maximum length of per-inode
prealloc list to 512 and allow users to modify it.

After patching, we observed that the sys ratio of cpu has dropped, and
the system throughput has increased significantly. We created a process
to write the sparse file, and the running time of the process on the
fixed kernel was significantly reduced, as follows:

Running time on unfixed kernel：
[root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
real    0m2.051s
user    0m0.008s
sys     0m2.026s

Running time on fixed kernel：
[root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
real    0m0.471s
user    0m0.004s
sys     0m0.395s

Signed-off-by: Chunguang Xu 
Link: https://lore.kernel.org/r/d7a98178-056b-6db5-6bce-4ead23f4a257@gmail.com
Signed-off-by: Theodore Ts'o 
Signed-off-by: Sasha Levin

x86/bugs/multihit: Fix mitigation reporting when VMX is not in use

2020-08-21T11:15:15+00:00

[ Upstream commit f29dfa53cc8ae6ad93bae619bcc0bf45cab344f7 ]

On systems that have virtualization disabled or unsupported, sysfs
mitigation for X86_BUG_ITLB_MULTIHIT is reported incorrectly as:

  $ cat /sys/devices/system/cpu/vulnerabilities/itlb_multihit
  KVM: Vulnerable

System is not vulnerable to DoS attack from a rogue guest when
virtualization is disabled or unsupported in the hardware. Change the
mitigation reporting for these cases.

Fixes: b8e8c8303ff2 ("kvm: mmu: ITLB_MULTIHIT mitigation")
Reported-by: Nelson Dsouza 
Co-developed-by: Sean Christopherson 
Signed-off-by: Sean Christopherson 
Signed-off-by: Pawan Gupta 
Signed-off-by: Ingo Molnar 
Reviewed-by: Tony Luck 
Acked-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/0ba029932a816179b9d14a30db38f0f11ef1f166.1594925782.git.pawan.kumar.gupta@linux.intel.com
Signed-off-by: Sasha Levin

Documentation: update for gcc 4.9 requirement

2020-07-08T19:28:44+00:00

Update Documentation for the gcc v4.9 upgrade requirement.

Fixes: 5429ef62bcf3 ("compiler/gcc: Raise minimum GCC version for kernel builds to 4.8")
Fixes: 6ec4476ac825 ("Raise gcc version requirement to 4.9")
Signed-off-by: Randy Dunlap 
Acked-by: Jonathan Corbet 
Signed-off-by: Linus Torvalds

Merge tag 'for-5.8/dm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

2020-06-27T15:57:16+00:00

Pull device mapper fixes from Mike Snitzer:

 - Quite a few DM zoned target fixes and a Zone append fix in DM core.

   Considering the amount of dm-zoned changes that went in during the
   5.8 merge window these fixes are not that surprising.

 - A few DM writecache target fixes.

 - A fix to Documentation index to include DM ebs target docs.

 - Small cleanup to use struct_size() in DM core's retrieve_deps().

* tag 'for-5.8/dm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm writecache: add cond_resched to loop in persistent_memory_claim()
  dm zoned: Fix reclaim zone selection
  dm zoned: Fix random zone reclaim selection
  dm: update original bio sector on Zone Append
  dm zoned: Fix metadata zone size check
  docs: device-mapper: add dm-ebs.rst to an index file
  dm ioctl: use struct_size() helper in retrieve_deps()
  dm writecache: skip writecache_wait when using pmem mode
  dm writecache: correct uncommitted_block when discarding uncommitted entry
  dm zoned: assign max_io_len correctly
  dm zoned: fix uninitialized pointer dereference

doc: THP CoW fault no longer allocate THP

2020-06-26T07:27:37+00:00

Since commit 3917c80280c9 ("thp: change CoW semantics for anon-THP"),
THP CoW page fault is rewritten.  Now it just splits pmd then fallback
to base page fault, it doesn't try to allocate THP anymore.  So it is no
longer counted in THP_FAULT_ALLOC.

Remove the obsolete statement in documentation about THP CoW allocation
to avoid confusion.

Link: http://lkml.kernel.org/r/1592424895-5421-1-git-send-email-yang.shi@linux.alibaba.com
Signed-off-by: Yang Shi 
Cc: Kirill A. Shutemov 
Cc: Zi Yan 
Cc: Jonathan Corbet 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

docs: device-mapper: add dm-ebs.rst to an index file

2020-06-19T16:21:56+00:00

Solves this Sphinx warning:
	Documentation/admin-guide/device-mapper/dm-ebs.rst: WARNING: document isn't included in any toctree

Signed-off-by: Mauro Carvalho Chehab 
Signed-off-by: Mike Snitzer

Merge tag 'docs-5.8-2' of git://git.lwn.net/linux

2020-06-10T21:12:15+00:00

Pull more documentation updates from Jonathan Corbet:
 "A handful of late-arriving docs fixes, along with a patch changing a
  lot of HTTP links to HTTPS that had to be yanked and redone before the
  first pull"

* tag 'docs-5.8-2' of git://git.lwn.net/linux:
  docs/memory-barriers.txt/kokr: smp_mb__{before,after}_atomic(): update Documentation
  Documentation: devres: add missing entry for devm_platform_get_and_ioremap_resource()
  Replace HTTP links with HTTPS ones: documentation
  docs: it_IT: address invalid reference warnings
  doc: zh_CN: use doc reference to resolve undefined label warning
  docs: Update the location of the LF NDA program
  docs: dev-tools: coccinelle: underlines

Merge branch 'akpm' (patches from Andrew)

2020-06-09T16:54:46+00:00

Merge even more updates from Andrew Morton:

 - a kernel-wide sweep of show_stack()

 - pagetable cleanups

 - abstract out accesses to mmap_sem - prep for mmap_sem scalability work

 - hch's user acess work

Subsystems affected by this patch series: debug, mm/pagemap, mm/maccess,
mm/documentation.

* emailed patches from Andrew Morton : (93 commits)
  include/linux/cache.h: expand documentation over __read_mostly
  maccess: return -ERANGE when probe_kernel_read() fails
  x86: use non-set_fs based maccess routines
  maccess: allow architectures to provide kernel probing directly
  maccess: move user access routines together
  maccess: always use strict semantics for probe_kernel_read
  maccess: remove strncpy_from_unsafe
  tracing/kprobes: handle mixed kernel/userspace probes better
  bpf: rework the compat kernel probe handling
  bpf:bpf_seq_printf(): handle potentially unsafe format string better
  bpf: handle the compat string in bpf_trace_copy_string better
  bpf: factor out a bpf_trace_copy_string helper
  maccess: unify the probe kernel arch hooks
  maccess: remove probe_read_common and probe_write_common
  maccess: rename strnlen_unsafe_user to strnlen_user_nofault
  maccess: rename strncpy_from_unsafe_strict to strncpy_from_kernel_nofault
  maccess: rename strncpy_from_unsafe_user to strncpy_from_user_nofault
  maccess: update the top of file comment
  maccess: clarify kerneldoc comments
  maccess: remove duplicate kerneldoc comments
  ...

mmap locking API: convert mmap_sem comments

2020-06-09T16:39:14+00:00

Convert comments that reference mmap_sem to reference mmap_lock instead.

[akpm@linux-foundation.org: fix up linux-next leftovers]
[akpm@linux-foundation.org: s/lockaphore/lock/, per Vlastimil]
[akpm@linux-foundation.org: more linux-next fixups, per Michel]

Signed-off-by: Michel Lespinasse 
Signed-off-by: Andrew Morton 
Reviewed-by: Vlastimil Babka 
Reviewed-by: Daniel Jordan 
Cc: Davidlohr Bueso 
Cc: David Rientjes 
Cc: Hugh Dickins 
Cc: Jason Gunthorpe 
Cc: Jerome Glisse 
Cc: John Hubbard 
Cc: Laurent Dufour 
Cc: Liam Howlett 
Cc: Matthew Wilcox 
Cc: Peter Zijlstra 
Cc: Ying Han 
Link: http://lkml.kernel.org/r/20200520052908.204642-13-walken@google.com
Signed-off-by: Linus Torvalds

Merge branch 'x86/srbds' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2020-06-09T16:30:21+00:00

Pull x86 srbds fixes from Thomas Gleixner:
 "The 9th episode of the dime novel "The performance killer" with the
  subtitle "Slow Randomizing Boosts Denial of Service".

  SRBDS is an MDS-like speculative side channel that can leak bits from
  the random number generator (RNG) across cores and threads. New
  microcode serializes the processor access during the execution of
  RDRAND and RDSEED. This ensures that the shared buffer is overwritten
  before it is released for reuse. This is equivalent to a full bus
  lock, which means that many threads running the RNG instructions in
  parallel have the same effect as the same amount of threads issuing a
  locked instruction targeting an address which requires locking of two
  cachelines at once.

  The mitigation support comes with the usual pile of unpleasant
  ingredients:

   - command line options

   - sysfs file

   - microcode checks

   - a list of vulnerable CPUs identified by model and stepping this
     time which requires stepping match support for the cpu match logic.

   - the inevitable slowdown of affected CPUs"

* branch 'x86/srbds' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/speculation: Add Ivy Bridge to affected list
  x86/speculation: Add SRBDS vulnerability and mitigation documentation
  x86/speculation: Add Special Register Buffer Data Sampling (SRBDS) mitigation
  x86/cpu: Add 'table' argument to cpu_matches()