amd64 kernel crash introduced between 20180329 & 20180408

[Kyle Evans]

On Tue, Apr 17, 2018 at 10:18 AM, Dan Allen <danallen46 at gmail.com> wrote:
>
>
>> On 17 Apr 2018, at 8:49 AM, Kyle Evans <kevans at freebsd.org> wrote:
>>
>> As "the guy most likely to have broken boot code in stable," may I ask
>> what leads you specifically to amd64 boot code? Mostly curious if
>> there's something beyond "i386 works well" that lead you to this
>> conclusion.
>
> It is partly just a hunch.
>
> I installed 11.0 for use with qemu a while ago.  I did binary upgrades for patches using
> freebsd-update.  When 11.1 came out, it would not work correctly, again with the same
> kind of behavior.  Then, I got some later snapshots that worked again, notably the 20180329
> build.  When the next snapshot came out, things broke.  I also tried my own builds, same story.
>
> I even got both source trees together - 20180329 and 20180408 - and did a diff on the entire
> trees, and I noticed activity in the boot & kernel code.  It could just as likely be something in the
> kernel as well, but none of this happens with the i386 build.
>
>> When you say it crashes and does a kernel dump- you're landing at a
>> ddb prompt, yeah? What does executing bt at that prompt look like?
>
> No, I am not ever given a prompt.  I get to watch a mini-dump happen and then an automatic
> reboot.  It is a kernel panic.  Here is what I see:
>

Ahh, fun. =)

I'm inclined to think it's probably not a boot code problem, but it is
suspicious. Can you set vm.pmap.pti=0 at the loader prompt and see if
this affects your situation at all, just to rule that out?