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Tom Lendacky df4d29732f perf/x86/amd: Change/fix NMI latency mitigation to use a timestamp 
It turns out that the NMI latency workaround from commit:

  6d3edaae16 ("x86/perf/amd: Resolve NMI latency issues for active PMCs")

ends up being too conservative and results in the perf NMI handler claiming
NMIs too easily on AMD hardware when the NMI watchdog is active.

This has an impact, for example, on the hpwdt (HPE watchdog timer) module.
This module can produce an NMI that is used to reset the system. It
registers an NMI handler for the NMI_UNKNOWN type and relies on the fact
that nothing has claimed an NMI so that its handler will be invoked when
the watchdog device produces an NMI. After the referenced commit, the
hpwdt module is unable to process its generated NMI if the NMI watchdog is
active, because the current NMI latency mitigation results in the NMI
being claimed by the perf NMI handler.

Update the AMD perf NMI latency mitigation workaround to, instead, use a
window of time. Whenever a PMC is handled in the perf NMI handler, set a
timestamp which will act as a perf NMI window. Any NMIs arriving within
that window will be claimed by perf. Anything outside that window will
not be claimed by perf. The value for the NMI window is set to 100 msecs.
This is a conservative value that easily covers any NMI latency in the
hardware. While this still results in a window in which the hpwdt module
will not receive its NMI, the window is now much, much smaller.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jerry Hoemann <jerry.hoemann@hpe.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 6d3edaae16 ("x86/perf/amd: Resolve NMI latency issues for active PMCs")
Link: https://lkml.kernel.org/r/Message-ID:
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 		2019-10-09 12:44:14 +02:00
Documentation Kbuild fixes for v5.4 2019-10-05 12:56:59 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch perf/x86/amd: Change/fix NMI latency mitigation to use a timestamp 2019-10-09 12:44:14 +02:00
block block: sed-opal: fix sparse warning: convert __be64 data 2019-10-03 14:21:32 -06:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
drivers ARM: SoC fixes 2019-10-05 17:18:43 -07:00
fs elf: don't use MAP_FIXED_NOREPLACE for elf executable mappings 2019-10-06 13:53:27 -07:00
include Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-10-05 08:50:15 -07:00
init Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
ipc ipc/sem.c: convert to use built-in RCU list checking 2019-09-25 17:51:41 -07:00
kernel perf/core: Fix corner case in perf_rotate_context() 2019-10-09 12:44:13 +02:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-10-05 08:50:15 -07:00
mm Merge branch 'hugepage-fallbacks' (hugepatch patches from David Rientjes) 2019-09-28 14:26:47 -07:00
net nfc: fix memory leak in llcp_sock_bind() 2019-10-04 18:31:36 -07:00
samples rpmsg updates for v5.4 2019-09-22 10:58:15 -07:00
scripts scripts/setlocalversion: clear local variable to make it work for sh 2019-10-05 15:29:49 +09:00
security integrity: remove pointless subdir-$(CONFIG_...) 2019-10-05 15:29:49 +09:00
sound sound fixes for 5.4-rc1 2019-09-24 16:46:16 -07:00
tools perf/urgent fixes: 2019-10-07 15:15:24 +02:00
usr kbuild: update compile-test header list for v5.4-rc2 2019-10-05 15:29:49 +09:00
virt KVM/arm fixes for 5.4, take #1 2019-10-03 12:08:50 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2019-09-18 12:34:53 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS CREDITS: Update email address 2019-09-13 17:21:38 +03:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS kgdb patches for 5.4-rc2 2019-10-03 11:17:57 -07:00
Makefile Linux 5.4-rc2 2019-10-06 14:27:30 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.