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Michael Ellerman 56376c5864 powerpc/kvm: Fix lockups when running KVM guests on Power8 
When running KVM guests on Power8 we can see a lockup where one CPU
stops responding. This often leads to a message such as:

  watchdog: CPU 136 detected hard LOCKUP on other CPUs 72
  Task dump for CPU 72:
  qemu-system-ppc R  running task    10560 20917  20908 0x00040004

And then backtraces on other CPUs, such as:

  Task dump for CPU 48:
  ksmd            R  running task    10032  1519      2 0x00000804
  Call Trace:
    ...
    --- interrupt: 901 at smp_call_function_many+0x3c8/0x460
        LR = smp_call_function_many+0x37c/0x460
    pmdp_invalidate+0x100/0x1b0
    __split_huge_pmd+0x52c/0xdb0
    try_to_unmap_one+0x764/0x8b0
    rmap_walk_anon+0x15c/0x370
    try_to_unmap+0xb4/0x170
    split_huge_page_to_list+0x148/0xa30
    try_to_merge_one_page+0xc8/0x990
    try_to_merge_with_ksm_page+0x74/0xf0
    ksm_scan_thread+0x10ec/0x1ac0
    kthread+0x160/0x1a0
    ret_from_kernel_thread+0x5c/0x78

This is caused by commit 8c1c7fb0b5 ("powerpc/64s/idle: avoid sync
for KVM state when waking from idle"), which added a check in
pnv_powersave_wakeup() to see if the kvm_hstate.hwthread_state is
already set to KVM_HWTHREAD_IN_KERNEL, and if so to skip the store and
test of kvm_hstate.hwthread_req.

The problem is that the primary does not set KVM_HWTHREAD_IN_KVM when
entering the guest, so it can then come out to cede with
KVM_HWTHREAD_IN_KERNEL set. It can then go idle in kvm_do_nap after
setting hwthread_req to 1, but because hwthread_state is still
KVM_HWTHREAD_IN_KERNEL we will skip the test of hwthread_req when we
wake up from idle and won't go to kvm_start_guest. From there the
thread will return somewhere garbage and crash.

Fix it by skipping the store of hwthread_state, but not the test of
hwthread_req, when coming out of idle. It's OK to skip the sync in
that case because hwthread_req will have been set on the same thread,
so there is no synchronisation required.

Fixes: 8c1c7fb0b5 ("powerpc/64s/idle: avoid sync for KVM state when waking from idle")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
 		2018-04-19 16:22:20 +10:00
..
boot powerpc updates for 4.17 2018-04-07 12:08:19 -07:00
configs scsi: remove the fdomain and fdomain_cs drivers 2018-03-19 22:54:47 -04:00
crypto crypto: hash - annotate algorithms taking optional key 2018-01-12 23:03:35 +11:00
include powerpc fixes for 4.17 #2 2018-04-15 11:57:12 -07:00
kernel powerpc/kvm: Fix lockups when running KVM guests on Power8 2018-04-19 16:22:20 +10:00
kvm powerpc fixes for 4.17 #2 2018-04-15 11:57:12 -07:00
lib powerpc/lib: Fix off-by-one in alternate feature patching 2018-04-17 00:37:48 +10:00
math-emu License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mm powerpc fixes for 4.17 #2 2018-04-15 11:57:12 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-03-05 11:29:24 -08:00
oprofile powerpc: Use sizeof(*foo) rather than sizeof(struct foo) 2018-03-20 16:47:53 +11:00
perf powerpc updates for 4.17 2018-04-07 12:08:19 -07:00
platforms powerpc fixes for 4.17 #2 2018-04-15 11:57:12 -07:00
purgatory License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sysdev powerpc/xive: Fix trying to "push" an already active pool VP 2018-04-19 00:49:45 +10:00
tools License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
xmon Merge branch 'topic/paca' into next 2018-03-31 09:09:36 +11:00
Kconfig kexec_file: make use of purgatory optional 2018-04-13 17:10:27 -07:00
Kconfig.debug powerpc: Add new kconfig CONFIG_PPC_IRQ_SOFT_MASK_DEBUG 2018-01-19 22:37:03 +11:00
Makefile powerpc/64s: Add POWER9 CPU type selection 2018-04-01 22:15:32 +10:00
Makefile.postlink License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00