Re: Regression between Xen 4.6.0 and 4.7.0, Direct kernel boot on a qemu-xen and seabios HVM guest doesn't work anymore.

[Wei Liu <wei.liu2@citrix.com>]

On Tue, Oct 18, 2016 at 01:48:23PM +0100, Wei Liu wrote:
> On Mon, Oct 17, 2016 at 05:28:17PM +0200, Sander Eikelenboom wrote:
> > Thursday, October 13, 2016, 4:43:31 PM, you wrote:
> > 
> > > Hi Jan / Wei,
> > 
> > > Took a while before i had the chance to fiddle some more to find the actual culprit.
> > > After analyzing the output of xl -vvvvv create somewhat more i came to the 
> > > insight it was probably Qemu and not Xen causing the fault.
> > 
> > > As a test I just used a qemu-xen binary build with xen-4.6.0 booting up a guest with
> > > direct kernel boot mode on xen-unstable. And that old qemu binary works fine.
> > 
> > > After testing i can conclude, Jan was right, the bisection was a red herring,
> > > the problem is caused by some change in Qemu and not by something in the Xen tree.
> > > (strange thing is that for as far as i know i did a "make distclean" between 
> > > every build (taking a lot of time), which should have pulled a fresh qemu-xen 
> > > tree and therefor the bisection should have lead to a commit with a Config.mk 
> > > hash change for qemu-xen version.)
> > 
> > > Will see if i can find some more time and bisect qemu and find the culprit.
> > 
> > > --
> > > Sander
> > 
> > 
> > Unfortunately i have to give up on this issue, for me it's impossible to bisect this 
> > issue with my present git-foo.
> > 
> > The first try with bisection of the whole xen-tree seems to have hit the issue that the 
> > qemu-revision that gets pulled on a fresh build is "master" during the whole
> > dev period. That creates havoc when trying to bisect, since you are testing 
> > combinations that were never developed (nor auto tested) in that combination
> > (especially when a xen-tree and qemu-tree change have a dependency like Roger's 
> > "xen: fix usage of xc_domain_create in domain builder")
> > 
> > While trying to bisect only qemu (keeping xen itself on RELEASE-4.6.0 and 
> > seabios on rel-1.8.2) it get stuck on issues with that tree.
> > Between 4.6.0 and 4.7.0 the qemu tree switched from git://xenbits.xen.org/qemu-upstream-4.6-testing.git
> > to git://xenbits.xen.org/qemu-xen.git),after that there seem to have 
> > been a lot of merges going back and forth and to me it seems a mess (but as i 
> > said it could also be a lack of git-foo). I tried by manual bisecting, removing 
> > and cloning trees again etc. but that doesn't suffice, it's all going no-where.
> > (while the known good build (plain RELEASE-4.6.0) always works, so it doesn't 
> > seem to be some random problem)
> > 
> 
> Thanks for trying.
> 
> > So perhaps some dev can at least verify that the issue is there (since 4.7.0)
> > and put it on the "known broken" list of things.
> > 
> 
> I will put this into the list of things I need to look at.
> 

I investigated this a bit. The root cause is the memory accounting is
wrong in QEMU. It would try to allocate more ram than allowed. I haven't
tried to figure out exactly what is wrong, though.

Wei.

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel