On 17/08/18 00:33, Andy Smith wrote: > Hi Juergen, > > As this was also addressed to -user I'm going to assume that you do > want user response as well.
Right. Thanks for responding. > > On Thu, Aug 16, 2018 at 08:17:13AM +0200, Juergen Gross wrote: >> We'd like to evaluate whether anyone would see problems with: >> >> - deprecating 32-bit PV guest support in Xen, meaning that we'd >> eventually switch to support 32-bit PV guests only via PV-shim from >> Xen 4.12 or 4.13 > > Although amd64 has been the default for us for many years, at the > moment we still have 64% of our customers running 32-bit PV. If > there remains a way for us to boot them through PV-shim and then > pvgrub2 with no functional changes and no work inside the guest then > that's fine, we'll adapt. > >> - dropping 32-bit PV support from upstream Linux kernel, resulting in >> current 32-bit PV guests no longer being able to upgrade to the newest >> kernel version any longer > > I doubt there is any technical reason why they can't switch to > 64-bit, it's just that in the majority of cases that involves a > complete reinstall and the users just haven't bothered to. Is something like missing Meltdown mitigation for 32-bit PV guest a technical reason? > If they are forced to switch because an impending kernel update will > leave them with a kernel that doesn't boot, they are going to be > upset that they are forced to reinstall their guest, or switch to a > 64-bit kernel with their existing 32-bit userland. > > It will of course help if they have plenty of warning that they need > to make the switch. But unless we're talking 2+ years of warning I'm > sure there will be some who will be unhappy. > > I was hoping to transition to PVH guests as soon as possible, but > last time I looked into it there was a problem booting the stable > Linux kernel under PVH, and also no support in grub2. Okay, noted. > Will it remain possible to boot a 32-bit Linux guest in PVH mode? Yes. > If so, could the final removal of 32-bit PV in the Linux kernel be > held off until there is: > > 1) a kernel shipping in Debian stable, Ubuntu LTS and CentOS that > boots under PVH, and; > > 2) support in grub2 so I can build a grub image that boots under > PVH? I think this is a reasonable request. > If grub PVH support is not going to happen, what is the roadmap for > user-specified guest kernels under PVH? I have a patch series lying around for grub2 PVH support. It requires some rework and another kernel enhancement. I'll try to resume work on the patches soon. > >> - is there any Linux distribution still shipping 32-bit PV-capable >> systems? > > Debian stable 32-bit kernels still boot under PV, as do Ubuntu 18.04 > LTS ones. Ubuntu LTS releases are supposed to be supported (by > Canonical) for 5 years, and while of course Xen does not fall under > the category of software that they support, there will be people > sticking with 18.04 LTS as long as they can. I guess they will stick to the stable kernel they are using now? Then this will be no problem. > I'm not saying that people running 32-bit PV Ubuntu 18.04 are right > to expect that to continue being supported until 2023. I'm just > saying that human nature dictates that those sorts of expectations > will exist. > > It will help a lot if there is an easy way for us to switch them > from 32-bit PV to PVH, while still letting them install their own > kernels. In the end it should be just a switch of domain type and boot loader (PV -> PVH, grubxen -> grubxen-pvh). The kernel needs to be configured to support PVH, of course. Thanks for the very valuable input! Juergen _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
