[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: We are not able to virtualize FreeBSD using xen 4.17 on Arm 32 bit
+(xen-devel and Arm maintainers, including Julien) > On Nov 27, 2023, at 18:03, Mario Marietto <marietto2008@xxxxxxxxx> wrote: > > Hello. > We have just virtualized Debian 12 on our arm (32 bit) Chromebook model > xe303c12 . As host / dom0 we have chosen Devuan 5,and for guest / domU,Debian > 12. It works great. But our goal is different. We want to virtualize FreeBSD > as domU. Can we have a working Xen PV network driver for a FreeBSD arm guest > ?. I found that Julien Grall has ported the Xen drivers to FreeBSD on arm. I > would like to know if Julien's work was accepted upstream by FreeBSD, in > which case FreeBSD as a Xen guest on arm should work if we enable the Xen PV > drivers in the FreeBSD on arm kernel. If Julien's work was not accepted > upstream by FreeBSD, we will have to find his patches and apply them > ourselves to the FreeBSD on arm kernel. > We found these slides : > > https://events.static.linuxfound.org/sites/events/files/slides/Porting%20FreeBSD%20on%20Xen%20on%20ARM%20.pdf > > Slide 13 refers to a XENHVM FreeBSD on arm kernel config - that is what we > want to find. > It looks like when that slide presentation was written, there were some > limitations on FreeBSD Xen guests. For example, for our debian bookworm > guest, I am using vcpus = '2' to match the number of real cpus on our > Chromebook, but slide 13 mentions support for only 1 VCPU with a FreeBSD > guest, so I will need to change that vcpus = '1' in the FreeBSD guest config > unless support for 2 or more vcpus was added later, which is possible because > that slide presentation is 9 years old. > Here is where I would expect to find the XENHVM FreeBSD on arm kernel config > file: > > https://cgit.freebsd.org/src/tree/sys/arm/conf > > But it is not there unless I am not understanding something correctly. For > now, unfortunately conclude that the support for Xen on arm that Julien Grall > mentioned in that slide presentation 9 years ago was never added to the > official FreeBSD source code. I am searching the web now to see if the > patches that Julien Grall wrote are still posted somewhere online. If we > cannot find them, we can ask here and on the xen-users mailing list. Julien > regularly reads that list and responds to questions about Xen on arm, so I > think he will tell us how to find the patches if we cannot find them online. > According to this page from the FreeBSD wiki: > > https://wiki.freebsd.org/Xen > > I think FreeBSD only supports Xen on x86, not arm. So this is going to be a > bit of a challenge to get a Xen FreeBSD guest on arm working. We know Julien > Grall has some patches that made it work in the past ! > I found a slightly newer slide presentation by Julien here: > > https://www.slideshare.net/xen_com_mgr/bsdcan-2015-how-to-port-your-bsd > > It is about the same, but it mentions the GENERIC FreeBSD kernel supports Xen > on arm64, but still says we need the XENHVM FreeBSD config for Xen on arm 32 > bit, which I haven't found online yet. > Please,take a look at this output of the linux kernel that can boot on Xen, > and the FreeBSD kernel that cannot : > > % file zImage-6.1.59-stb-xen-cbe+ > zImage-6.1.59-stb-xen-cbe+: Linux kernel ARM boot executable zImage > (little-endian) > > % file FREEBSD-XENVIRT > FREEBSD-XENVIRT: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), > dynamically linked, interpreter /red/herring, for FreeBSD 11.0 (1100048), not > stripped > > > The FreeBSD kernel that won't boot is in ELF format but the Linux kernel that > does boot is in zImage format. This is the error we get : > # xl create freebsd.cfg > Parsing config from freebsd.cfg xc: error: panic: xg_dom_elfloader.c:63: > xc_dom_guest_type: image not capable of booting inside a HV > M container: Invalid kernel > libxl: error: libxl_dom.c:571:libxl__build_dom: xc_dom_parse_image failed > libxl: error: libxl_create.c:1640:domcreate_rebuild_done: Domain 4:cannot > (re-)build domain: -3 > libxl: error: libxl_domain.c:1183:libxl__destroy_domid: Domain 4:Non-existant > domain > libxl: error: libxl_domain.c:1137:domain_destroy_callback: Domain 4:Unable to > destroy guest > libxl: error: libxl_domain.c:1064:domain_destroy_cb: Domain 4:Destruction of > domain failed > > We are spending time reading the docs on xenbits.xenproject.org, and > according to those docs Xen on arm only knows how to boot a kernel in the > zImage format, so the FreeBSD kernel is in a format that modern Xen > incorrectly detects as an x86 kernel. > I also watched Julien Grall's 30 minute video presentation of his work to > boot FreeBSD/arm on Xen at FOSDEM 2014 here : > > https://archive.fosdem.org/2014/schedule/event/freebsd_xen_arm/ > > In that video, and in other places, Julien mentions that the boot ABI for > FreeBSD/arm on Xen was not yet developed and he was getting occasional > crashes and needed to investigate the problem. He mentioned the zImage ABI > that Linux uses, but pointed out FreeBSD does not use that format, and back > then it was an open question which format to use to boot FreeBSD/arm on Xen. > Unfortunately, nine years later, the only supported format is still the > zImage format that Linux uses. > It looks like Julien's work back then was using an ELF binary to boot > FreeBSD/arm on Xen instead of the supported zImage format that Linux uses and > the modern Xen toolstack exits with an error when trying to boot the FreeBSD > ELF formatted binary that Julien's patch creates. So the best solution would > be to try to port the rules to build a FreeBSD kernel in the zImage format > instead of the ELF format. I have been studying the Makefiles in Linux to see > how Linux builds the Linux arm kernel in the zImage format, but it is not > trivial to understand. > -- > Mario.
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