Re: kvm crash on 5.7-rc1 and later

[Peter Zijlstra]

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.
> 
> [   61.576664] kernel BUG at arch/x86/kvm/x86.c:387!
> [   61.576672] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> [   61.576678] CPU: 0 PID: 3851 Comm: qemu-system-x86 Not tainted 5.7-pingu
> #0
> [   61.576680] Hardware name: LENOVO 20B6005JUS/20B6005JUS, BIOS GJETA4WW
> (2.54 ) 03/27/2020
> [   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:   Sun Jan 26 12:05:35 2020 -0800
> 
>     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.