To clarify, we're only really talking about the kernel here? So, if
(like me) you've upgraded your kernel and hence your Xen instance to 64
bit, but your userland is a mixture of 32 and 64 bit, you're OK?
(In my case: debian stretch, kernel 4.9. Clearly I ought to upgrade to
buster, which will enable PVH mode, but rather than continue with my ~8
years of cruft around the filesystem, did you say something about being
able to offer a spare guests on a short term basis for the purposes of
reimaging? I really ought get my head around Ansible and friends too...)
Ross
On 16/07/19 10:05 PM, Andy Smith wrote:
Hi,
Those running 32-bit VMs who haven't thought about
upgrading/reinstalling them to 64-bit yet, please have a read of:
“There are no current plans to remove support for 32bit PV
guests from Xen, but it is very much in the category of "you
shouldn't be using this mode any more".”
https://lists.xenproject.org/archives/html/xen-devel/2019-07/msg00827.html
When Juergen asked for feedback on removing 32-bit guest support a
year or two ago I told him that (at the time) more than 60% of
BitFolk's user base was 32-bit and they'd need time to transition.
Now that there is a stable grub release which supports PVH¹ booting
Juergen is pushing this again and it will eventually go through to
the Linux kernel.
When Xen does remove 32-bit PV mode we can still continue to support
32-bit guests in PVH mode or HVM mode, so I will still make sure it
works without customers having to do anything. But you should be
clear that just because it will work doesn't mean it is a good idea!
I have a round of updates to do and then I will start moving
customers over to PVH mode where possible (requires 4.11+ kernel in
guest).
Cheers,
Andy
¹ PVH mode guests run all the normal code paths of a kernel not
under virtualisation except for their IO drivers like networking
and block devices which are still paravirtualised for performance
reasons. This results in a kernel that has a smaller attack
surface as there is much less xen-specific code being used, it's
faster and simpler. It also still doesn't require use of qemu on
BitFolk's side. See:
https://wiki.xen.org/wiki/Understanding_the_Virtualization_Spectrum
for more information.
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