On 03/06/2018 01:34 AM, Martin Schwidefsky wrote:
On Mon, 5 Mar 2018 20:08:45 +0100 Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote:Do you happen to run with a recent host kernel that has commit 7041d28115e91f2144f811ffe8a195c696b1e1d0 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 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -426,13 +426,13 @@ ENTRY(system_call) UPDATE_VTIME %r8,%r9,__LC_SYNC_ENTER_TIMER BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP stmg %r0,%r7,__PT_R0(%r11) - # clear user controlled register to prevent speculative use - xgr %r0,%r0 mvc __PT_R8(64,%r11),__LC_SAVE_AREA_SYNC mvc __PT_PSW(16,%r11),__LC_SVC_OLD_PSW mvc __PT_INT_CODE(4,%r11),__LC_SVC_ILC stg %r14,__PT_FLAGS(%r11) .Lsysc_do_svc: + # clear user controlled register to prevent speculative use + xgr %r0,%r0 # load address of system call table lg %r10,__THREAD_sysc_table(%r13,%r12) llgh %r8,__PT_INT_CODE+2(%r11) 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 critical section cleanup. 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 :)
Thanks Farhan -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
