Re: kvm crash on 5.7-rc1 and later

[Xiaoyao Li]

On 7/12/2020 2:21 AM, Peter Zijlstra wrote:
> On Fri, Jul 03, 2020 at 11:15:31AM -0400, Woody Suwalski wrote:
> > I am observing a 100% reproducible kvm crash on kernels starting with
> > 5.7-rc1, always with the same opcode 0000.
> > It happens during wake up from the host suspended state. Worked OK on 5.6
> > and older.
> > The host is based on Debian testing, Thinkpad T440, i5 cpu.
> >
> > [ÂÂ 61.576664] kernel BUG at arch/x86/kvm/x86.c:387!
> > [ÂÂ 61.576672] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> > [ÂÂ 61.576678] CPU: 0 PID: 3851 Comm: qemu-system-x86 Not tainted 5.7-pingu
> > #0
> > [ÂÂ 61.576680] Hardware name: LENOVO 20B6005JUS/20B6005JUS, BIOS GJETA4WW
> > (2.54 ) 03/27/2020
> > [ÂÂ 61.576700] RIP: 0010:kvm_spurious_fault+0xa/0x10 [kvm]
> >
> > Crash results in a dead kvm and occasionally a very unstable system.
> >
> > Bisecting the problem between v5.6 and v5.7-rc1 points to
> >
> > commit 6650cdd9a8ccf00555dbbe743d58541ad8feb6a7
> > Author: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > Date:ÂÂ Sun Jan 26 12:05:35 2020 -0800
> >
> >  ÂÂÂ x86/split_lock: Enable split lock detection by kernel
> >
> > Reversing that patch seems to actually "cure" the issue.
> >
> > The problem is present in all kernels past 5.7-rc1, however the patch is not
> > reversing directly in later source trees, so can not retest the logic on
> > recent kernels.
> >
> > Peter, would you have idea how to debug that (or even better - would you
> > happen to know the fix)?
> >
> > I have attached dmesg logs from a "good" 5.6.9 kernel, and then "bad" 5.7.0
> > and 5.8-rc3
>
> I have no clue about kvm. Nor do I actually have hardware with SLD on.
> I've Cc'ed a bunch of folks who might have more ideas.

I think this bug is the same as the one found by Sean, and is already 
fixed in 5.8-rc4.

https://lore.kernel.org/kvm/20200605192605.7439-1-sean.j.christopherson@xxxxxxxxx/