Re: Xen 4.18.5 PV dbregs fail

[Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>]

On Mon, May 26, 2025 at 07:17:13PM +0100, Andrew Cooper wrote:
> On 26/05/2025 7:06 pm, Andrew Cooper wrote:
> > On 26/05/2025 6:59 pm, Manuel Bouyer wrote:
> >> Hello,
> >> since I updated to Xen 4.18.5 (from 4.18.4), NetBSD's dbregs-related tests
> >> are failing. Only for PV; PVH and HVM guests are fine. They are
> >> failing for both 32bits and 64bits guests.
> >>
> >> I tracked it down to dr6 being 0xffff0ff0 after the trace trap, when at
> >> last one of the lower bits should be 1 (I think it's bit 0, from the code).
> >>
> >> I looked at the commit log between 4.18.4 and 4.18.5 but didn't see
> >> anything obvious.
> >>
> >> Any idea ?
> >>
> > Have you got a link to the test in question?
> >
> > We've had a couple of bugfixes in this area, although debug handling
> > isn't helped by the fact that both the SDM and APM are factually
> > incorrect on how to write a #DB handler (and the vendors are moving at a
> > glacial pace to correct them).
> 
> But yes, having looked between 4.18.4 and 4.18.5, I can't see anything
> relevant to debug handling either.
> 
> Judging from your description, it looks like a breakpoint is going missing.
> 
> The relevant recent change for that is
> https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=54ef601a66e8d812a6a6a308f02524e81201825e
> although it's a bit older than 4.18.4.

Well, my previous xen-debug.gz kernel is from Oct, 3 so it can't be
4.18.4, it's 4.18.3_20240909 which points to commit
bd51e573a730efc569646379cd59ccba967cde97

looks like I forgot to update this server. So I need to looks deeper in
the commit logs

-- 
Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
     NetBSD: 26 ans d'experience feront toujours la difference
--