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5388a5b821
linux/arch/arm/include/asm
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Russell King 5388a5b821 ARM: avoid Cortex-A9 livelock on tight dmb loops 
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 <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
2019-02-01 22:05:50 +00:00
..
hardware ARM: sa1111: remove legacy GPIO interfaces 2018-12-04 22:37:38 +00:00
mach Merge branch 'x86-timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-08-13 18:28:19 -07:00
xen License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
arch_gicv3.h irqchip/gic-v3: Probe for SCR_EL3 being clear before resetting AP0Rn 2018-03-22 13:46:18 +00:00
arch_timer.h arm64 updates for 4.15 2017-11-15 10:56:56 -08:00
arm-cci.h
asm-offsets.h
assembler.h ARM: 8812/1: Optimise copy_{from/to}_user for !CPU_USE_DOMAINS 2018-11-12 10:51:59 +00:00
atomic.h atomics/treewide: Clean up '*_andnot()' ifdeffery 2018-06-21 14:25:24 +02:00
auxvec.h
barrier.h ARM: avoid Cortex-A9 livelock on tight dmb loops 2019-02-01 22:05:50 +00:00
bitops.h ARM: 8785/1: use compiler built-ins for ffs and fls 2018-07-30 11:45:53 +01:00
bitrev.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
bL_switcher.h
bug.h signal/arm: Push siginfo generation into arm_notify_die 2018-09-27 21:55:30 +02:00
bugs.h ARM: bugs: hook processor bug checking into SMP and suspend paths 2018-05-31 10:39:29 +01:00
cache.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
cacheflush.h docs: Fix some broken references 2018-06-15 18:10:01 -03:00
cachetype.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
checksum.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
clocksource.h arm/arm64: arch_timer: Use archdata to indicate vdso suitability 2016-09-23 17:19:25 +01:00
cmpxchg.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
compiler.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
cp15.h ARM: spectre-v2: harden user aborts in kernel space 2018-05-31 10:40:32 +01:00
cpu.h
cpufeature.h ARM: 8663/1: wire up HWCAP/HWCAP2 feature bits to the CPU modalias 2017-03-30 19:45:52 +01:00
cpuidle.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
cputype.h Merge branches 'misc', 'sa1100-for-next' and 'spectre' into for-linus 2019-01-02 10:37:05 +00:00
cti.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dcc.h
delay.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
device.h ARM: dma-mapping: Don't tear down third-party mappings 2017-05-30 11:31:33 +02:00
div64.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dma-contiguous.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dma-direct.h dma/direct: Handle the memory encryption bit in common code 2018-03-20 10:01:59 +01:00
dma-iommu.h arm: remove the mapping_error dma_map_ops method 2018-12-06 06:56:37 -08:00
dma-mapping.h dma-mapping: bypass indirect calls for dma-direct 2018-12-13 21:06:18 +01:00
dma.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dmi.h efi/arm: Enable DMI/SMBIOS 2017-06-05 17:50:44 +02:00
domain.h ARM: 8573/1: domain: move {set,get}_domain under config guard 2016-05-05 19:03:02 +01:00
ecard.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
edac.h
efi.h efi: Deduplicate efi_open_volume() 2018-07-22 14:13:43 +02:00
elf.h Merge branch 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm 2017-11-16 12:50:35 -08:00
entry-macro-multi.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
exception.h ARM: probes: avoid adding kprobes to sensitive kernel-entry/exit code 2017-12-17 22:14:21 +00:00
fb.h
fiq.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
firmware.h
fixmap.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
flat.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
floppy.h ARM: 8584/1: floppy: avoid gcc-6 warning 2016-07-02 11:02:13 +01:00
fncpy.h
fpstate.h
ftrace.h ARM: 8788/1: ftrace: remove old mcount support 2018-09-19 10:44:50 +01:00
futex.h Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
glue-cache.h ARM: 8725/1: Add Broadcom Brahma-B15 readahead cache support 2017-12-17 22:15:35 +00:00
glue-df.h
glue-pf.h
glue-proc.h
glue.h
gpio.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
hardirq.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
highmem.h Merge branch 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm 2017-11-16 12:50:35 -08:00
hugetlb-3level.h hugetlb: introduce generic version of huge_ptep_get 2018-10-26 16:26:34 -07:00
hugetlb.h hugetlb: introduce generic version of huge_ptep_get 2018-10-26 16:26:34 -07:00
hw_breakpoint.h perf/hw_breakpoint: Remove default hw_breakpoint_arch_parse() 2018-06-26 09:07:58 +02:00
hw_irq.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
hwcap.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
hypervisor.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ide.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
idmap.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
insn.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
io.h xen: don't include <xen/xen.h> from <asm/io.h> and <asm/dma-mapping.h> 2018-09-26 08:45:18 -06:00
irq_work.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
irq.h ARM: Convert to GENERIC_IRQ_MULTI_HANDLER 2018-08-03 12:14:08 +02:00
irqflags.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
jump_label.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kbuild time: Add an asm-generic/compat.h file 2018-04-19 13:28:51 +02:00
kexec.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
kgdb.h ARM: 8764/1: kgdb: fix NUMREGBYTES so that gdb_regs[] is the correct size 2018-05-19 11:53:46 +01:00
kmap_types.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
kprobes.h ARM/kprobes: Remove jprobe arm implementation 2018-06-21 12:33:07 +02:00
krait-l2-accessors.h ARM: Add Krait L2 register accessor functions 2018-10-17 13:14:33 -07:00
kvm_arm.h KVM updates for v4.20 2018-10-25 17:57:35 -07:00
kvm_asm.h arm/arm64: KVM: Add ARM_EXCEPTION_IS_TRAP macro 2018-12-19 17:47:53 +00:00
kvm_coproc.h KVM: arm: plug potential guest hardware debug leakage 2017-05-15 14:29:19 +02:00
kvm_emulate.h KVM/arm updates for 4.19 2018-08-22 14:07:56 +02:00
kvm_host.h * ARM: selftests improvements, large PUD support for HugeTLB, 2018-12-26 11:46:28 -08:00
kvm_hyp.h KVM: arm/arm64: Avoid VGICv3 save/restore on VHE with no IRQs 2018-03-19 10:53:21 +00:00
kvm_mmio.h KVM: arm/arm64: Export mmio_read/write_bus 2016-05-20 15:39:42 +02:00
kvm_mmu.h KVM: arm64: Add support for creating PUD hugepages at stage 2 2018-12-18 15:14:49 +00:00
limits.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
linkage.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mc146818rtc.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mcpm.h
mcs_spinlock.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
memblock.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
memory.h linux/const.h: move UL() macro to include/linux/const.h 2018-04-11 10:28:38 -07:00
mmu_context.h sched/headers: Prepare to remove the <linux/mm_types.h> dependency from <linux/sched.h> 2017-03-02 08:42:37 +01:00
mmu.h Merge branch 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm 2017-11-16 12:50:35 -08:00
module.h ARM: module: Fix function kallsyms on Thumb-2 2018-12-14 20:27:29 +01:00
mpu.h ARM: 8757/1: NOMMU: Support PMSAv8 MPU 2018-05-19 11:53:46 +01:00
mtd-xip.h
neon.h
nwflash.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
opcodes-sec.h
opcodes-virt.h
opcodes.h
outercache.h
page-nommu.h ARM: 8684/1: NOMMU: Remove unused KTHREAD_SIZE definition 2017-06-27 14:58:10 +01:00
page.h
paravirt.h x86/paravirt: Use a single ops structure 2018-09-03 16:50:35 +02:00
patch.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
pci.h PCI: remove PCI_DMA_BUS_IS_PHYS 2018-05-07 07:15:41 +02:00
percpu.h
perf_event.h
pgalloc.h mm: treewide: remove unused address argument from pte_alloc functions 2019-01-04 13:13:47 -08:00
pgtable-2level-hwdef.h ARM: 8612/1: LPAE: initialize cache policy correctly 2016-09-12 12:12:30 +01:00
pgtable-2level-types.h
pgtable-2level.h mm: make the __PAGETABLE_PxD_FOLDED defines non-empty 2018-11-02 08:31:52 +01:00
pgtable-3level-hwdef.h ARM: 8612/1: LPAE: initialize cache policy correctly 2016-09-12 12:12:30 +01:00
pgtable-3level-types.h
pgtable-3level.h mm: introduce ARCH_HAS_PTE_SPECIAL 2018-06-07 17:34:35 -07:00
pgtable-hwdef.h
pgtable-nommu.h ARM: 8676/1: NOMMU: provide pgprot_device() macro 2017-06-05 10:29:40 +01:00
pgtable.h ARM: 8823/1: Implement pgprot_device() 2019-02-01 21:44:11 +00:00
probes.h ARM/kprobes: Remove jprobe arm implementation 2018-06-21 12:33:07 +02:00
proc-fns.h ARM: spectre-v2: per-CPU vtables to work around big.Little systems 2018-11-12 10:51:01 +00:00
processor.h ARM: avoid Cortex-A9 livelock on tight dmb loops 2019-02-01 22:05:50 +00:00
procinfo.h
prom.h
psci.h ARM: SoC cleanups for v4.5 2016-01-20 17:55:20 -08:00
ptdump.h ARM: 8737/1: mm: dump: add checking for writable and executable 2018-01-21 15:32:20 +00:00
ptrace.h linux/compiler.h: Split into compiler.h and compiler_types.h 2017-10-24 13:17:32 +02:00
sections.h ARM: probes: avoid adding kprobes to sensitive kernel-entry/exit code 2017-12-17 22:14:21 +00:00
secure_cntvoff.h ARM: smp: Add initialization of CNTVOFF 2018-05-08 14:50:42 +02:00
set_memory.h treewide: move set_memory_* functions away from cacheflush.h 2017-05-08 17:15:13 -07:00
setup.h ARM: 8495/1: ATAGS: move save_atags() to arch/arm/include/asm/setup.h 2016-01-04 11:26:00 +00:00
shmparam.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
signal.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
smp_plat.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
smp_scu.h ARM: SoC platform updates for 4.15 2017-11-16 14:05:12 -08:00
smp_twd.h ARM: 8822/1: smp_twd: Remove legacy TWD registration 2019-02-01 21:44:10 +00:00
smp.h ARM: 8708/1: NOMMU: Rework MPU to be mostly done in C 2017-10-23 16:58:59 +01:00
sparsemem.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
spinlock_types.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
spinlock.h ARM: 8829/1: spinlock: use unified assembler language syntax 2019-02-01 21:44:15 +00:00
stackprotector.h ARM: smp: add support for per-task stack canaries 2018-12-12 13:20:07 -08:00
stacktrace.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
stage2_pgtable.h arm: KVM: Add S2_PMD_{MASK,SIZE} constants 2018-12-19 17:48:21 +00:00
string.h ARM: 8745/1: get rid of __memzero() 2018-01-21 15:37:56 +00:00
suspend.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
swab.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
switch_to.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sync_bitops.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
syscall.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
system_info.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
system_misc.h ARM: spectre-v2: harden user aborts in kernel space 2018-05-31 10:40:32 +01:00
tcm.h
therm.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
thread_info.h ARM: smp: add support for per-task stack canaries 2018-12-12 13:20:07 -08:00
thread_notify.h
timex.h
tlb.h arm/asm/tlb.h: Fix build error implicit func declaration 2018-07-25 12:09:09 +02:00
tlbflush.h sched/headers: Prepare to remove the <linux/mm_types.h> dependency from <linux/sched.h> 2017-03-02 08:42:37 +01:00
tls.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
topology.h sched/topology, arch/arm: Rebuild sched_domain hierarchy when CPU capacity changes 2018-09-10 11:05:48 +02:00
traps.h ARM: probes: avoid adding kprobes to sensitive kernel-entry/exit code 2017-12-17 22:14:21 +00:00
trusted_foundations.h treewide: remove redundant #include <linux/kconfig.h> 2016-10-11 15:06:33 -07:00
uaccess.h ARM: 8828/1: uaccess: use unified assembler language syntax 2019-02-01 21:44:14 +00:00
ucontext.h Merge branch 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm 2017-11-16 12:50:35 -08:00
unaligned.h ARM: 8715/1: add a private asm/unaligned.h 2017-10-24 10:33:23 +01:00
unified.h ARM: 8723/2: always assume the "unified" syntax for assembly code 2017-12-17 22:14:21 +00:00
unistd.h y2038: Compile utimes()/futimesat() conditionally 2018-08-29 15:42:23 +02:00
unwind.h
uprobes.h
user.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
v7m.h ARM: 8830/1: NOMMU: Toggle only bits in EXC_RETURN we are really care of 2019-02-01 21:44:19 +00:00
vdso_datapage.h
vdso.h ARM: 8748/1: mm: Define vdso_start, vdso_end as array 2018-03-24 14:27:49 +00:00
vfp.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vfpmacros.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vga.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
virt.h ARM: hyp-stub/KVM: Kill __hyp_get_vectors 2017-04-09 07:49:34 -07:00
word-at-a-time.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
xor.h