Re: [Xen-users] pvgrub2(-like?) booting methods for PVHv2 guests

[Juergen Gross <jgross@xxxxxxxx>]

On 24/01/18 17:37, Hans van Kranenburg wrote:
> On 01/23/2018 06:41 AM, Juergen Gross wrote:
>> On 23/01/18 05:46, Andy Smith wrote:
>>> Hi,
>>>
>>> What are the current options for booting PVHv2 guests in Xen 4.10.0?
>>>
>>> As far as I can see there is only direct kernel booting, i.e.
>>> supplying "kernel = /path/to/vmlinux".
>>>
>>> In PV land there is pvgrub which is very convenient for being able
>>> to use kernel and initramfs, but I am not seeing support for that in
>>> upstream grub2. I see that Juergen Gross post a patch series that
>>> claims to add this feature:
>>>
>>>     <https://lists.gnu.org/archive/html/grub-devel/2017-11/msg00054.html>
>>>
>>> …but this doesn't seem to have been applied yet. Is it an ongoing
>>> idea or has that method been abandoned?
>>
>> Still waiting for review.
> 
> Since I wanted to try to test this, I scraped the patches off the
> grub-devel list and did the following:
> 
> 1. clone https://git.savannah.gnu.org/git/grub.git
> 2. apply patches on top of master, plus an extra one with a puzzle piece
> to make it actually compile (see attachment)
> 
> 3. build:
> ./autogen.sh
> ./configure --target=i386 --with-platform=xenpvh
> make
> 
> 4. use mkstandalone to create a grub image to boot
> ./grub-mkstandalone -d grub-core --locale-directory=/ -o
> ~/grub-i386-xenpvh-fire-ze-missile -O i386-xenpvh
> ~/build/pvgrub2/pvgrub2/xvda-fire-ze-missile.cfg
> 
> contents of the config file that I want to have inserted into it (same
> file I use for booting PV now):
> 
> root='(xen/xvda)'
> insmod xzio
> insmod gzio
> insmod btrfs
> insmod ext2
> echo 'Loading Linux ...'
> linux /vmlinuz root=/dev/xvda ro elevator=noop
> echo 'Loading initial ramdisk ...'
> initrd /initrd.img
> boot
> 
> 5. Try to use it already, to see what happens. (Xen 4.10.0)
> 
> -# cat yolo-pvgrub2
> 
> type="pvh"
> kernel = "/yolo/grub-i386-xenpvh-fire-ze-missile"
> name = "yolo-pvgrub2"
> memory = 1024
> vcpus = 10
> vif = [
>     "mac=02:00:0a:8c:d9:0d,bridge=ovs0.217",
> ]
> disk = [
>     '/dev/test/yolo,raw,xvda,rw',
> ]
> 
> -# xen create -c yolo-pvgrub2
> Parsing config from yolo-pvgrub2
> libxl: info: libxl_create.c:109:libxl__domain_build_info_setdefault:
> qemu-xen is unavailable, using qemu-xen-traditional instead: No such
> file or directory
> S3 disabled
> S4 disabled
> CONV disabled
> 
>                      GNU GRUB  version 2.03
> 
>    Minimal BASH-like line editing is supported. For the first word, TAB
>    lists possible command completions. Anywhere else TAB lists possible
>    device or file completions.
> 
> 
> grub>
> 
> Ok, so for some reason it seems to ignore the config? But I can type
> things manually:
> 
> grub> insmod xzio
> grub> insmod gzio
> grub> insmod btrfs
> grub> insmod ext2
> grub> search.file /vmlinuz
>  xen/xvda
> 
> Ok, so it can see the disk and fine the symlink to the kernel image. Now
> let's try the rest of it:
> 
> grub> root='(xen/xvda)'
> grub> linux /vmlinuz root=/dev/xvda ro elevator=noop
> grub> initrd /initrd.img
> grub> boot
> 
> And now it just hangs, no output any more.
> 
> 6. Apply linux patches to the domU kernel and Xen
> 
> domU Linux kernel:
> - Branch off from linux 4.14.14
> - add https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git as
> remote and cherry-pick the 4 patches mentioned in
>   https://lists.gnu.org/archive/html/grub-devel/2017-12/msg00017.html
> 
> Xen: pick this one on top of 4.10.0:
>  https://lists.xen.org/archives/html/xen-devel/2017-11/msg01807.html
>  4a5733771e6f33918eba07b584cccce564a67ac1
> 
> 7. Test again after dom0 reboot into the new xen and put the new domU
> kernel on it.
>  -> same result: grub command prompt, and no activity after 'boot'.
> 
> Extra things:
> 
> 8. Start domU after copying kernel/initrd to the dom0:
> 
> type="pvh"
> kernel = "/yolo/vmlinuz-4.14.14-yolo"
> ramdisk = "/yolo/initrd.img-4.14.14-yolo"
> root = "/dev/xvda ro elevator=noop console=hvc0"
> 
> This boots, dmesg: http://paste.debian.net/plainh/7120cef2
> 
> 9. Just for fun, start domU with previous kernel/initrd without the patches:
> 
> type="pvh"
> kernel = "/yolo/vmlinuz-4.14.0-3-amd64"
> ramdisk = "/yolo/initrd.img-4.14.0-3-amd64"
> root = "/dev/xvda ro elevator=noop console=hvc0"
> 
> This boots and has 1 vcpu and no ACPI lines in dmesg, which is expected
> breakage, I believe, reading xen-devel.
> 
> So, what am I missing?

I used the attached script to build it (derived from the pvgrub build
script used in SUSE's grub-xen RPM).


Juergen

Attachment: mk
Description: Text document

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