Re: port-xen/57199: Pure PVH i386 guests hang on disk activity

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

> Date: Mon, 15 Jul 2024 14:31:41 -0400
> From: Brad Spencer <brad%anduin.eldar.org@localhost>
> 
> b) I will test Taylor's patch on the DOMU.  Doing that on the DOM0 is
> probably not something I can manage right now.

I should clarify: I suspect this may be needed on the dom0, but only
if the dom0 _also_ runs uniprocessor, i.e., single-vCPU.

If you can run crash(8) or enter ddb on the dom0, you can check like
so:

# crash
Crash version 10.0_STABLE, image version 10.0.
WARNING: versions differ, you may not be able to examine this image.
Kernel compiled without options LOCKDEBUG.
Output from a running system is unreliable.
crash> x/i membar_sync,3
_membar_enter:  lock addq       $0,fffffffffffffff8 (%rsp)
_membar_enter+0x7:      ret
_membar_enter+0x8:      nopl

If it says `lock addq' or `lock addl', you're good.  If it's just
`addq' or `addl' with no `lock', the patch is needed.