From: Michael Ellerman <mpe@ellerman.id.au>
To: linuxppc-dev@ozlabs.org
Cc: npiggin@gmail.com, paulus@samba.org
Subject: [PATCH] powerpc/kvm: Fix lockups when running KVM guests on Power8
Date: Thu, 19 Apr 2018 23:29:50 +1000 [thread overview]
Message-ID: <20180419132950.16752-1-mpe@ellerman.id.au> (raw)
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>
---
arch/powerpc/kernel/idle_book3s.S | 4 ++--
1 file 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
--
2.14.1
next reply other threads:[~2018-04-19 13:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-19 13:29 Michael Ellerman [this message]
2018-04-19 13:42 ` powerpc/kvm: Fix lockups when running KVM guests on Power8 Michael Ellerman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180419132950.16752-1-mpe@ellerman.id.au \
--to=mpe@ellerman.id.au \
--cc=linuxppc-dev@ozlabs.org \
--cc=npiggin@gmail.com \
--cc=paulus@samba.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.