linux-stable.git/arch/arm/include/asm/processor.h, branch v4.4.232

ARM: avoid Cortex-A9 livelock on tight dmb loops

2019-04-27T07:33:52+00:00

[ Upstream commit 5388a5b82199facacd3d7ac0d05aca6e8f902fed ]

machine_crash_nonpanic_core() does this:

	while (1)
		cpu_relax();

because the kernel has crashed, and we have no known safe way to deal
with the CPU.  So, we place the CPU into an infinite loop which we
expect it to never exit - at least not until the system as a whole is
reset by some method.

In the absence of erratum 754327, this code assembles to:

	b	.

In other words, an infinite loop.  When erratum 754327 is enabled,
this becomes:

1:	dmb
	b	1b

It has been observed that on some systems (eg, OMAP4) where, if a
crash is triggered, the system tries to kexec into the panic kernel,
but fails after taking the secondary CPU down - placing it into one
of these loops.  This causes the system to livelock, and the most
noticable effect is the system stops after issuing:

	Loading crashdump kernel...

to the system console.

The tested as working solution I came up with was to add wfe() to
these infinite loops thusly:

	while (1) {
		cpu_relax();
		wfe();
	}

which, without 754327 builds to:

1:	wfe
	b	1b

or with 754327 is enabled:

1:	dmb
	wfe
	b	1b

Adding "wfe" does two things depending on the environment we're running
under:
- where we're running on bare metal, and the processor implements
  "wfe", it stops us spinning endlessly in a loop where we're never
  going to do any useful work.
- if we're running in a VM, it allows the CPU to be given back to the
  hypervisor and rescheduled for other purposes (maybe a different VM)
  rather than wasting CPU cycles inside a crashed VM.

However, in light of erratum 794072, Will Deacon wanted to see 10 nops
as well - which is reasonable to cover the case where we have erratum
754327 enabled _and_ we have a processor that doesn't implement the
wfe hint.

So, we now end up with:

1:      wfe
        b       1b

when erratum 754327 is disabled, or:

1:      dmb
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        nop
        wfe
        b       1b

when erratum 754327 is enabled.  We also get the dmb + 10 nop
sequence elsewhere in the kernel, in terminating loops.

This is reasonable - it means we get the workaround for erratum
794072 when erratum 754327 is enabled, but still relinquish the dead
processor - either by placing it in a lower power mode when wfe is
implemented as such or by returning it to the hypervisior, or in the
case where wfe is a no-op, we use the workaround specified in erratum
794072 to avoid the problem.

These as two entirely orthogonal problems - the 10 nops addresses
erratum 794072, and the wfe is an optimisation that makes the system
more efficient when crashed either in terms of power consumption or
by allowing the host/other VMs to make use of the CPU.

I don't see any reason not to use kexec() inside a VM - it has the
potential to provide automated recovery from a failure of the VMs
kernel with the opportunity for saving a crashdump of the failure.
A panic() with a reboot timeout won't do that, and reading the
libvirt documentation, setting on_reboot to "preserve" won't either
(the documentation states "The preserve action for an on_reboot event
is treated as a destroy".)  Surely it has to be a good thing to
avoiding having CPUs spinning inside a VM that is doing no useful
work.

Acked-by: Will Deacon 
Signed-off-by: Russell King 
Signed-off-by: Sasha Levin

arch, locking: Ciao arch_mutex_cpu_relax()

2014-07-17T10:32:47+00:00

The arch_mutex_cpu_relax() function, introduced by 34b133f, is
hacky and ugly. It was added a few years ago to address the fact
that common cpu_relax() calls include yielding on s390, and thus
impact the optimistic spinning functionality of mutexes. Nowadays
we use this function well beyond mutexes: rwsem, qrwlock, mcs and
lockref. Since the macro that defines the call is in the mutex header,
any users must include mutex.h and the naming is misleading as well.

This patch (i) renames the call to cpu_relax_lowlatency  ("relax, but
only if you can do it with very low latency") and (ii) defines it in
each arch's asm/processor.h local header, just like for regular cpu_relax
functions. On all archs, except s390, cpu_relax_lowlatency is simply cpu_relax,
and thus we can take it out of mutex.h. While this can seem redundant,
I believe it is a good choice as it allows us to move out arch specific
logic from generic locking primitives and enables future(?) archs to
transparently define it, similarly to System Z.

Signed-off-by: Davidlohr Bueso 
Signed-off-by: Peter Zijlstra 
Cc: Andrew Morton 
Cc: Anton Blanchard 
Cc: Aurelien Jacquiot 
Cc: Benjamin Herrenschmidt 
Cc: Bharat Bhushan 
Cc: Catalin Marinas 
Cc: Chen Liqin 
Cc: Chris Metcalf 
Cc: Christian Borntraeger 
Cc: Chris Zankel 
Cc: David Howells 
Cc: David S. Miller 
Cc: Deepthi Dharwar 
Cc: Dominik Dingel 
Cc: Fenghua Yu 
Cc: Geert Uytterhoeven 
Cc: Guan Xuetao 
Cc: Haavard Skinnemoen 
Cc: Hans-Christian Egtvedt 
Cc: Heiko Carstens 
Cc: Helge Deller 
Cc: Hirokazu Takata 
Cc: Ivan Kokshaysky 
Cc: James E.J. Bottomley 
Cc: James Hogan 
Cc: Jason Wang 
Cc: Jesper Nilsson 
Cc: Joe Perches 
Cc: Jonas Bonn 
Cc: Joseph Myers 
Cc: Kees Cook 
Cc: Koichi Yasutake 
Cc: Lennox Wu 
Cc: Linus Torvalds 
Cc: Mark Salter 
Cc: Martin Schwidefsky 
Cc: Matt Turner 
Cc: Max Filippov 
Cc: Michael Neuling 
Cc: Michal Simek 
Cc: Mikael Starvik 
Cc: Nicolas Pitre 
Cc: Paolo Bonzini 
Cc: Paul Burton 
Cc: Paul E. McKenney 
Cc: Paul Gortmaker 
Cc: Paul Mackerras 
Cc: Qais Yousef 
Cc: Qiaowei Ren 
Cc: Rafael Wysocki 
Cc: Ralf Baechle 
Cc: Richard Henderson 
Cc: Richard Kuo 
Cc: Russell King 
Cc: Steven Miao 
Cc: Steven Rostedt 
Cc: Stratos Karafotis 
Cc: Tim Chen 
Cc: Tony Luck 
Cc: Vasily Kulikov 
Cc: Vineet Gupta 
Cc: Vineet Gupta 
Cc: Waiman Long 
Cc: Will Deacon 
Cc: Wolfram Sang 
Cc: adi-buildroot-devel@lists.sourceforge.net
Cc: linux390@de.ibm.com
Cc: linux-alpha@vger.kernel.org
Cc: linux-am33-list@redhat.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-c6x-dev@linux-c6x.org
Cc: linux-cris-kernel@axis.com
Cc: linux-hexagon@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux@lists.openrisc.net
Cc: linux-m32r-ja@ml.linux-m32r.org
Cc: linux-m32r@ml.linux-m32r.org
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-metag@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1404079773.2619.4.camel@buesod1.americas.hpqcorp.net
Signed-off-by: Ingo Molnar

ARM: prefetch: add support for prefetchw using pldw on SMP ARMv7+ CPUs

2013-09-30T15:42:55+00:00

SMP ARMv7 CPUs implement the pldw instruction, which allows them to
prefetch data cachelines in an exclusive state.

This patch defines the prefetchw macro using pldw for CPUs that support
it.

Acked-by: Nicolas Pitre 
Signed-off-by: Will Deacon

ARM: smp_on_up: move inline asm ALT_SMP patching macro out of spinlock.h

2013-09-30T15:42:55+00:00

Patching UP/SMP alternatives inside inline assembly blocks is useful
outside of the spinlock implementation, where it is used for sev and wfe.

This patch lifts the macro into processor.h and gives it a scarier name
to (a) avoid conflicts in the global namespace and (b) to try and deter
its usage unless you "know what you're doing". The W macro for generating
wide instructions when targetting Thumb-2 is also made available under
the name WASM, to reduce the potential for conflicts with other headers.

Acked-by: Nicolas Pitre 
Signed-off-by: Will Deacon

ARM: prefetch: remove redundant "cc" clobber

2013-09-30T15:42:55+00:00

The pld instruction does not affect the condition flags, so don't bother
clobbering them.

Acked-by: Nicolas Pitre 
Signed-off-by: Will Deacon

ARM: 7791/1: a.out: remove partial a.out support

2013-07-26T11:02:10+00:00

a.out support on ARM requires that argc, argv and envp are passed in
r0-r2 respectively, which requires hacking load_aout_binary to
prevent argc being clobbered by the return code. Whilst mainline kernels
do set the registers up in start_thread, the aout loader has never
carried the hack in mainline.

Initialising the registers in this way actually goes against the libc
expectations for ELF binaries, where argc, argv and envp are passed on
the stack, with r0 being used to hold a pointer to an exit function for
cleaning up after the dynamic linker if required. If the pointer is
NULL, then it is ignored. When execing an ELF binary, Linux currently
zeroes r0, then sets it to argc and then finally clobbers it with the
return value of the execve syscall, so we actually end up with:

	r0 = 0
	stack[0] = argc
	r1 = stack[1] = argv
	r2 = stack[2] = envp

libc treats r1 and r2 as undefined. The clobbering of r0 by sys_execve
works for user-spawned threads, but when executing an ELF binary from a
kernel thread (via call_usermodehelper), the execve is performed on the
ret_from_fork path, which restores r0 from the saved pt_regs, resulting
in argc being presented to the C library. This has horrible consequences
when the application exits, since we have an exit function registered
using argc, resulting in a jump to hyperspace.

This patch solves the problem by removing the partial a.out support from
arch/arm/ altogether.

Cc: 
Cc: Ashish Sangwan 
Signed-off-by: Will Deacon 
Signed-off-by: Russell King

arm: split ret_from_fork, simplify kernel_thread() [based on patch by rmk]

2012-10-01T02:21:36+00:00

Signed-off-by: Al Viro

Merge branch 'x86-fpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2012-05-23T17:59:07+00:00

Pull fpu state cleanups from Ingo Molnar:
 "This tree streamlines further aspects of FPU handling by eliminating
  the prepare_to_copy() complication and moving that logic to
  arch_dup_task_struct().

  It also fixes the FPU dumps in threaded core dumps, removes and old
  (and now invalid) assumption plus micro-optimizes the exit path by
  avoiding an FPU save for dead tasks."

Fixed up trivial add-add conflict in arch/sh/kernel/process.c that came
in because we now do the FPU handling in arch_dup_task_struct() rather
than the legacy (and now gone) prepare_to_copy().

* 'x86-fpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86, fpu: drop the fpu state during thread exit
  x86, xsave: remove thread_has_fpu() bug check in __sanitize_i387_state()
  coredump: ensure the fpu state is flushed for proper multi-threaded core dump
  fork: move the real prepare_to_copy() users to arch_dup_task_struct()

fork: move the real prepare_to_copy() users to arch_dup_task_struct()

2012-05-16T22:16:26+00:00

Historical prepare_to_copy() is mostly a no-op, duplicated for majority of
the architectures and the rest following the x86 model of flushing the extended
register state like fpu there.

Remove it and use the arch_dup_task_struct() instead.

Suggested-by: Oleg Nesterov 
Suggested-by: Linus Torvalds 
Signed-off-by: Suresh Siddha 
Link: http://lkml.kernel.org/r/1336692811-30576-1-git-send-email-suresh.b.siddha@intel.com
Acked-by: Benjamin Herrenschmidt 
Cc: David Howells 
Cc: Koichi Yasutake 
Cc: Paul Mackerras 
Cc: Paul Mundt 
Cc: Chris Zankel 
Cc: Richard Henderson 
Cc: Russell King 
Cc: Haavard Skinnemoen 
Cc: Mike Frysinger 
Cc: Mark Salter 
Cc: Aurelien Jacquiot 
Cc: Mikael Starvik 
Cc: Yoshinori Sato 
Cc: Richard Kuo 
Cc: Tony Luck 
Cc: Michal Simek 
Cc: Ralf Baechle 
Cc: Jonas Bonn 
Cc: James E.J. Bottomley 
Cc: Helge Deller 
Cc: Martin Schwidefsky 
Cc: Heiko Carstens 
Cc: Chen Liqin 
Cc: Lennox Wu 
Cc: David S. Miller 
Cc: Chris Metcalf 
Cc: Jeff Dike 
Cc: Richard Weinberger 
Cc: Guan Xuetao 
Signed-off-by: H. Peter Anvin

arm: Remove unused cpu_idle_wait()

2012-05-08T10:35:06+00:00

cpuidle uses a generic function now. Remove the unused code.

Signed-off-by: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Russell King 
Link: http://lkml.kernel.org/r/20120507175652.260797846@linutronix.de