On 03/06/2018 01:34 AM, Martin Schwidefsky wrote:
On Mon, 5 Mar 2018 20:08:45 +0100
Christian Borntraeger <borntrae...@de.ibm.com> wrote:
Do you happen to run with a recent host kernel that has
s390: scrub registers on kernel entry and KVM exit
Can you run with this on top
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 13a133a6015c..d6dc0e5e8f74 100644
@@ -426,13 +426,13 @@ ENTRY(system_call)
- # clear user controlled register to prevent speculative use
- xgr %r0,%r0
+ # clear user controlled register to prevent speculative use
+ xgr %r0,%r0
# load address of system call table
To me it looks like that the critical section cleanup (interrupt during system
call entry) might
save the registers again into ptregs but we have already zeroed out r0.
This patch moves the clearing of r0 after sysc_do_svc, which should fix the
Adding Martin and Heiko. Will spin a patch.
Argh, yes. Thanks Chrisitan, this is it. I have been searching for the bug
for days now. The point is that if the system call handler is interrupted
after the xgr but before .Lsysc_do_svc the code at .Lcleanup_system_call
repeats the stmg for %r0-%r7 but now %r0 is already zero.
Please commit a patch for this and I'll will queue it up immediately.
This patch does fix the QEMU crash. I haven't seen the crash after
running the test case for more than a day. Thanks to everyone for taking
a look at this problem :)