Re: [Xen-devel] [Xen-users] Future of 32-bit PV support
On 20/08/18 18:01, Hans van Kranenburg wrote:
> On 08/17/2018 06:09 AM, Juergen Gross wrote:
>> On 17/08/18 00:33, Andy Smith wrote:
>>> Hi Juergen,
>>>
>>> [...]
>>> 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.
>
> +1, Yes please!
>
> Do I understand correctly ('another kernel enhancement') that you found
> more things which need to be done than the 32-bit memory map limitation
> issue at the grub side?
The kernel is still lacking support for handing over RSDP address from
grub to the kernel. The initial patches adding that haven't been taken
as several distributions are shipping a patched grub2 which is breaking
the grub/kernel boot protocol by clobbering kernel data.
I need to extend that protocol to detect such a clobbering in order to
be able to tell the difference between grub having set a new parameter
or just written garbage to it.
Juergen
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Re: [Xen-devel] [Xen-users] Future of 32-bit PV support
On 08/17/2018 06:09 AM, Juergen Gross wrote:
> On 17/08/18 00:33, Andy Smith wrote:
>> Hi Juergen,
>>
>> [...]
>> 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.
+1, Yes please!
Do I understand correctly ('another kernel enhancement') that you found
more things which need to be done than the 32-bit memory map limitation
issue at the grub side?
>> [...]
Thanks,
Hans
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Re: [Xen-devel] [Xen-users] Future of 32-bit PV support
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
Re: [Xen-devel] [Xen-users] Future of 32-bit PV support
Hi Juergen, As this was also addressed to -user I'm going to assume that you do want user response as well. 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. 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. Will it remain possible to boot a 32-bit Linux guest in PVH mode? 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? If grub PVH support is not going to happen, what is the roadmap for user-specified guest kernels under PVH? > - 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'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. Cheers, Andy ___ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
