powerpc: move arch_trigger_cpumask_backtrace from nmi.h to irq.h

The powerpc architecture was the only one that defined
arch_trigger_cpumask_backtrace() in asm/nmi.h instead of
asm/irq.h. Move it to be consistent.

This fixes compile time errors introduced by commit 7ca8fe94aa92
("watchdog/hardlockup: define HARDLOCKUP_DETECTOR_ARCH"). That commit
caused <asm/nmi.h> to stop being included if the hardlockup detector
wasn't enabled. The specific errors were:
error: implicit declaration of function `nmi_cpu_backtrace'
error: implicit declaration of function `nmi_trigger_cpumask_backtrace'

NOTE: when moving this into irq.h, we also change the guards from just
checking if "CONFIG_NMI_IPI" is defined to also checking if
"CONFIG_PPC_BOOK3S_64" is defined. This matches the code in
arch/powerpc/kernel/stacktrace.c. Previously this worked because
<asm.nmi.h> was included if "CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH" was
defined. For powerpc that's only selected if "CONFIG_PPC_BOOK3S_64" is
defined.

[dianders@chromium.org: change the guards to include CONFIG_PPC_BOOK3S_64]
Link: https://lkml.kernel.org/r/20230622202816.v2.1.Ice67126857506712559078e7de26d32d26e64631@changeid
Link: https://lkml.kernel.org/r/20230621164809.1.Ice67126857506712559078e7de26d32d26e64631@changeid
Fixes: 7ca8fe94aa92 ("watchdog/hardlockup: define HARDLOCKUP_DETECTOR_ARCH")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Closes: https://lore.kernel.org/r/871qi5otdh.fsf@mail.lhotse
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tom Rix <trix@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

watchdog/hardlockup: declare arch_touch_nmi_watchdog() only in linux/nmi.h

arch_touch_nmi_watchdog() needs a different implementation for various
hardlockup detector implementations. And it does nothing when
any hardlockup detector is not built at all.

arch_touch_nmi_watchdog() is declared via linux/nmi.h. And it must be
defined as an empty function when there is no hardlockup detector.
It is done directly in this header file for the perf and buddy detectors.
And it is done in the included asm/linux.h for arch specific detectors.

The reason probably is that the arch specific variants build the code
using another conditions. For example, powerpc64/sparc64 builds the code
when CONFIG_PPC_WATCHDOG is enabled.

Another reason might be that these architectures define more functions
in asm/nmi.h anyway.

However the generic code actually knows when the function will be
implemented. It happens when some full featured or the sparc64-specific
hardlockup detector is built.

In particular, CONFIG_HARDLOCKUP_DETECTOR can be enabled only when
a generic or arch-specific full featured hardlockup detector is available.
The only exception is sparc64 which can be built even when the global
HARDLOCKUP_DETECTOR switch is disabled.

The information about sparc64 is a bit complicated. The hardlockup
detector is built there when CONFIG_HAVE_NMI_WATCHDOG is set and
CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH is not set.

People might wonder whether this change really makes things easier.
The motivation is:

+ The current logic in linux/nmi.h is far from obvious.
For example, arch_touch_nmi_watchdog() is defined as {} when
neither CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER nor
CONFIG_HAVE_NMI_WATCHDOG is defined.

+ The change synchronizes the checks in lib/Kconfig.debug and
in the generic code.

+ It is a step that will help cleaning HAVE_NMI_WATCHDOG related
checks.

The change should not change the existing behavior.

Link: https://lkml.kernel.org/r/20230616150618.6073-4-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

watchdog/hardlockup: rename some "NMI watchdog" constants/function

Do a search and replace of:
- NMI_WATCHDOG_ENABLED => WATCHDOG_HARDLOCKUP_ENABLED
- SOFT_WATCHDOG_ENABLED => WATCHDOG_SOFTOCKUP_ENABLED
- watchdog_nmi_ => watchdog_hardlockup_
- nmi_watchdog_available => watchdog_hardlockup_available
- nmi_watchdog_user_enabled => watchdog_hardlockup_user_enabled
- soft_watchdog_user_enabled => watchdog_softlockup_user_enabled
- NMI_WATCHDOG_DEFAULT => WATCHDOG_HARDLOCKUP_DEFAULT

Then update a few comments near where names were changed.

This is specifically to make it less confusing when we want to introduce
the buddy hardlockup detector, which isn't using NMIs. As part of this,
we sanitized a few names for consistency.

[trix@redhat.com: make variables static]
Link: https://lkml.kernel.org/r/20230525162822.1.I0fb41d138d158c9230573eaa37dc56afa2fb14ee@changeid
Link: https://lkml.kernel.org/r/20230519101840.v5.12.I91f7277bab4bf8c0cb238732ed92e7ce7bbd71a6@changeid
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Tom Rix <trix@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Colin Cross <ccross@android.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Lecopzer Chen <lecopzer.chen@mediatek.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masayoshi Mizuma <msys.mizuma@gmail.com>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Pingfan Liu <kernelfans@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
Cc: Ricardo Neri <ricardo.neri@intel.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: Sumit Garg <sumit.garg@linaro.org>
Cc: Tzung-Bi Shih <tzungbi@chromium.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

powerpc/watchdog: introduce a NMI watchdog's factor

Introduce a factor which would apply to the NMI watchdog timeout.

This factor is a percentage added to the watchdog_tresh value. The value is
set under the watchdog_mutex protection and lockup_detector_reconfigure()
is called to recompute wd_panic_timeout_tb.

Once the factor is set, it remains until it is set back to 0, which means
no impact.

Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220713154729.80789-4-ldufour@linux.ibm.com

powerpc: Fix STACKTRACE=n build

Our skiroot_defconfig doesn't enable FTRACE, and so doesn't get
STACKTRACE enabled either. That leads to a build failure since commit
1614b2b11fab ("arch: Make ARCH_STACKWALK independent of STACKTRACE")
made stacktrace.c build even when STACKTRACE=n.

arch/powerpc/kernel/stacktrace.c: In function ‘handle_backtrace_ipi’:
arch/powerpc/kernel/stacktrace.c:171:2: error: implicit declaration of function ‘nmi_cpu_backtrace’
171 | nmi_cpu_backtrace(regs);
| ^~~~~~~~~~~~~~~~~
arch/powerpc/kernel/stacktrace.c: In function ‘arch_trigger_cpumask_backtrace’:
arch/powerpc/kernel/stacktrace.c:226:2: error: implicit declaration of function ‘nmi_trigger_cpumask_backtrace’
226 | nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This happens because our headers haven't defined
arch_trigger_cpumask_backtrace, which causes lib/nmi_backtrace.c not to
build nmi_cpu_backtrace().

The code in question doesn't actually depend on STACKTRACE=y, that was
just added because arch_trigger_cpumask_backtrace() lived in
stacktrace.c for convenience. So drop the dependency on
CONFIG_STACKTRACE, that causes lib/nmi_backtrace.c to build
nmi_cpu_backtrace() etc. and fixes the build.

Fixes: 1614b2b11fab ("arch: Make ARCH_STACKWALK independent of STACKTRACE")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220212111349.2806972-1-mpe@ellerman.id.au

powerpc: Fix STACKTRACE=n build

Our skiroot_defconfig doesn't enable FTRACE, and so doesn't get
STACKTRACE enabled either. That leads to a build failure since commit
1614b2b11fab ("arch: Make ARCH_STACKWALK independent of STACKTRACE")
made stacktrace.c build even when STACKTRACE=n.

arch/powerpc/kernel/stacktrace.c: In function ‘handle_backtrace_ipi’:
arch/powerpc/kernel/stacktrace.c:171:2: error: implicit declaration of function ‘nmi_cpu_backtrace’
171 | nmi_cpu_backtrace(regs);
| ^~~~~~~~~~~~~~~~~
arch/powerpc/kernel/stacktrace.c: In function ‘arch_trigger_cpumask_backtrace’:
arch/powerpc/kernel/stacktrace.c:226:2: error: implicit declaration of function ‘nmi_trigger_cpumask_backtrace’
226 | nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This happens because our headers haven't defined
arch_trigger_cpumask_backtrace, which causes lib/nmi_backtrace.c not to
build nmi_cpu_backtrace().

The code in question doesn't actually depend on STACKTRACE=y, that was
just added because arch_trigger_cpumask_backtrace() lived in
stacktrace.c for convenience. So drop the dependency on
CONFIG_STACKTRACE, that causes lib/nmi_backtrace.c to build
nmi_cpu_backtrace() etc. and fixes the build.

Fixes: 1614b2b11fab ("arch: Make ARCH_STACKWALK independent of STACKTRACE")
[mpe: Cherry pick of 5a72345e6a78 from next into fixes]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220212111349.2806972-1-mpe@ellerman.id.au

powerpc: convert interrupt handlers to use wrappers

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210130130852.2952424-29-npiggin@gmail.com

powerpc/watchdog: Declare soft_nmi_interrupt() prototype

soft_nmi_interrupt() usage requires PPC_WATCHDOG to be configured.
Check the CONFIG definition to declare the prototype.

It fixes this W=1 compile error :

../arch/powerpc/kernel/watchdog.c:250:6: error: no previous prototype for ‘soft_nmi_interrupt’ [-Werror=missing-prototypes]
250 | void soft_nmi_interrupt(struct pt_regs *regs)
| ^~~~~~~~~~~~~~~~~~

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210104143206.695198-18-clg@kaod.org

powerpc/64s: Fix HV NMI vs HV interrupt recoverability test

HV interrupts that use HSRR registers do not enter with MSR[RI] clear,
but their entry code is not recoverable vs NMI, due to shared use of
HSPRG1 as a scratch register to save r13.

This means that a system reset or machine check that hits in HSRR
interrupt entry can cause r13 to be silently corrupted.

Fix this by marking NMIs non-recoverable if they land in HV interrupt
ranges.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

powerpc/64s: Fix build failures with CONFIG_NMI_IPI=n

I broke the build when CONFIG_NMI_IPI=n with my recent commit to add
arch_trigger_cpumask_backtrace(), eg:

stacktrace.c:(.text+0x1b0): undefined reference to `.smp_send_safe_nmi_ipi'

We should rework the CONFIG symbols here in future to avoid these
double barrelled ifdefs but for now they fix the build.

Fixes: 5cc05910f26e ("powerpc/64s: Wire up arch_trigger_cpumask_backtrace()")
Reported-by: Christophe LEROY <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

powerpc/64s: Wire up arch_trigger_cpumask_backtrace()

This allows eg. the RCU stall detector, or the soft/hardlockup
detectors to trigger a backtrace on all CPUs.

We implement this by sending a "safe" NMI, which will actually only
send an IPI. Unfortunately the generic code prints "NMI", so that's a
little confusing but we can probably live with it.

If one of the CPUs doesn't respond to the IPI, we then print some info
from it's paca and do a backtrace based on its saved_r1.

Example output:

INFO: rcu_sched detected stalls on CPUs/tasks:
2-...0: (0 ticks this GP) idle=1be/1/4611686018427387904 softirq=1055/1055 fqs=25735
(detected by 4, t=58847 jiffies, g=58, c=57, q=1258)
Sending NMI from CPU 4 to CPUs 2:
CPU 2 didn't respond to backtrace IPI, inspecting paca.
irq_soft_mask: 0x01 in_mce: 0 in_nmi: 0 current: 3623 (bash)
Back trace of paca->saved_r1 (0xc0000000e1c83ba0) (possibly stale):
Call Trace:
[c0000000e1c83ba0] [0000000000000014] 0x14 (unreliable)
[c0000000e1c83bc0] [c000000000765798] lkdtm_do_action+0x48/0x80
[c0000000e1c83bf0] [c000000000765a40] direct_entry+0x110/0x1b0
[c0000000e1c83c90] [c00000000058e650] full_proxy_write+0x90/0xe0
[c0000000e1c83ce0] [c0000000003aae3c] __vfs_write+0x6c/0x1f0
[c0000000e1c83d80] [c0000000003ab214] vfs_write+0xd4/0x240
[c0000000e1c83dd0] [c0000000003ab5cc] ksys_write+0x6c/0x110
[c0000000e1c83e30] [c00000000000b860] system_call+0x58/0x6c

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

powerpc/watchdog: remove arch_trigger_cpumask_backtrace

The powerpc NMI IPIs may not be recoverable if they are taken in
some sections of code, and also there have been and still are issues
with taking NMIs (in KVM guest code, in firmware, etc) which makes them
a bit dangerous to use.

Generic code like softlockup detector and rcu stall detectors really
hammer on trigger_*_backtrace, which has lead to further problems
because we've implemented it with the NMI.

So stop providing NMI backtraces for now. Importantly, the powerpc code
uses NMI IPIs in crash/debug, and the SMP hardlockup watchdog. So if the
softlockup and rcu hang detection traces are not being printed because
the CPU is stuck with interrupts off, then the hard lockup watchdog
should get it with the NMI IPI.

Fixes: 2104180a5369 ("powerpc/64s: implement arch-specific hardlockup watchdog")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

License cleanup: add SPDX GPL-2.0 license identifier to files with no license

Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.

For non */uapi/* files that summary was:

SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139

and resulted in the first patch in this series.

If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:

SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930

and resulted in the second patch in this series.

- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:

SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1

and that resulted in the third patch in this series.

- when the two scanners agreed on the detected license(s), that became
the concluded license(s).

- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.

- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).

- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.

- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct

This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

powerpc/64: Fix watchdog configuration regressions

This fixes a couple more bits of fallout from the new hard lockup watchdog
patch.

It restores the required hw_nmi_get_sample_period() function for the
perf watchdog, and removes some function declarations on 64e that are only
defined for 64s. This fixes the 64e build when the hardlockup detector is
enabled.

It restores the default behaviour of disabling the perf watchdog, and also
fixes disabling the 64s watchdog when running as a guest.

Fixes: 2104180a53 ("powerpc/64s: implement arch-specific hardlockup watchdog")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

powerpc/64s: implement arch-specific hardlockup watchdog

Implement an arch-speicfic watchdog rather than use the perf-based
hardlockup detector.

The new watchdog takes the soft-NMI directly, rather than going through
perf. Perf interrupts are to be made maskable in future, so that would
prevent the perf detector from working in those regions.

Additionally, implement a SMP based detector where all CPUs watch one
another by pinging a shared cpumask. This is because powerpc Book3S
does not have a true periodic local NMI, but some platforms do implement
a true NMI IPI.

If a CPU is stuck with interrupts hard disabled, the soft-NMI watchdog
does not work, but the SMP watchdog will. Even on platforms without a
true NMI IPI to get a good trace from the stuck CPU, other CPUs will
notice the lockup sufficiently to report it and panic.

[npiggin@gmail.com: honor watchdog disable at boot/hotplug]
Link: http://lkml.kernel.org/r/20170621001346.5bb337c9@roar.ozlabs.ibm.com
[npiggin@gmail.com: fix false positive warning at CPU unplug]
Link: http://lkml.kernel.org/r/20170630080740.20766-1-npiggin@gmail.com
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170616065715.18390-6-npiggin@gmail.com
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Tested-by: Babu Moger <babu.moger@oracle.com> [sparc]
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

powerpc: Add ppc64 hard lockup detector support

The hard lockup detector uses a PMU event as a periodic NMI to
detect if we are stuck (where stuck means no timer interrupts have
occurred).

Ben's rework of the ppc64 soft disable code has made ppc64 PMU
exceptions a partial NMI. They can get disabled if an external
interrupt comes in, but otherwise PMU interrupts will fire in
interrupt disabled regions.

We disable the hard lockup detector by default for a few reasons:

- It breaks userspace event based branches on POWER8.
- It is likely to produce false positives on KVM guests.
- Since PMCs can only count to 2^31, counting cycles means we might
take multiple PMU exceptions per second per hardware thread even
if our hard lockup timeout is 10 seconds.

It can be enabled via a boot option, or via procfs.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>