Re: [Xen-devel] 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.

[Håkon Alstadheim <hakon@xxxxxxxxxxxxxxxxxx>]

Den 18. okt. 2016 14:48, skrev Wei Liu:
> 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.
>
> Wei.
>
In the mean time, a viable work-around is to use pxe boot if one needs
external boot for hvm under xen-4.7.

Still, the effort is appreciated :-).
Regards, Håkon.

P.S: I had some difficulty with pxe-boot and serial console, feel free
to email me direct if anyone wants to compare notes.


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