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| author | Michael Ellerman <mpe@ellerman.id.au> | 2018-04-19 09:22:20 +0300 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2018-04-19 09:22:20 +0300 |
| commit | 56376c5864f8ff4ba7c78a80ae857eee3b1d23d8 (patch) | |
| tree | 489c1bb5876431b2d692bd9f6bdde6a0b04f9875 /arch/powerpc/kernel/idle_book3s.S | |
| parent | 13a83eac373c49c0a081cbcd137e79210fe78acd (diff) | |
| download | linux-56376c5864f8ff4ba7c78a80ae857eee3b1d23d8.tar.xz | |
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 8c1c7fb0b5ec ("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: 8c1c7fb0b5ec ("powerpc/64s/idle: avoid sync for KVM state when waking from idle")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/idle_book3s.S')
| -rw-r--r-- | arch/powerpc/kernel/idle_book3s.S | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S index 79d005445c6c..e734f6e45abc 100644 --- a/arch/powerpc/kernel/idle_book3s.S +++ b/arch/powerpc/kernel/idle_book3s.S @@ -553,12 +553,12 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300) #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE lbz r0,HSTATE_HWTHREAD_STATE(r13) cmpwi r0,KVM_HWTHREAD_IN_KERNEL - beq 1f + beq 0f li r0,KVM_HWTHREAD_IN_KERNEL stb r0,HSTATE_HWTHREAD_STATE(r13) /* Order setting hwthread_state vs. testing hwthread_req */ sync - lbz r0,HSTATE_HWTHREAD_REQ(r13) +0: lbz r0,HSTATE_HWTHREAD_REQ(r13) cmpwi r0,0 beq 1f b kvm_start_guest |