Messages in this thread | | | Subject | Re: [Xen-devel] [PATCH 0/2] Remove 32-bit Xen PV guest support | From | Juergen Gross <> | Date | Tue, 16 Jul 2019 05:55:20 +0200 |
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On 15.07.19 19:39, Andrew Cooper wrote: > On 15/07/2019 18:28, Andy Lutomirski wrote: >> On Mon, Jul 15, 2019 at 9:34 AM Andi Kleen <ak@linux.intel.com> wrote: >>> Juergen Gross <jgross@suse.com> writes: >>> >>>> The long term plan has been to replace Xen PV guests by PVH. The first >>>> victim of that plan are now 32-bit PV guests, as those are used only >>>> rather seldom these days. Xen on x86 requires 64-bit support and with >>>> Grub2 now supporting PVH officially since version 2.04 there is no >>>> need to keep 32-bit PV guest support alive in the Linux kernel. >>>> Additionally Meltdown mitigation is not available in the kernel running >>>> as 32-bit PV guest, so dropping this mode makes sense from security >>>> point of view, too. >>> Normally we have a deprecation period for feature removals like this. >>> You would make the kernel print a warning for some releases, and when >>> no user complains you can then remove. If a user complains you can't. >>> >> As I understand it, the kernel rules do allow changes like this even >> if there's a complaint: this is a patch that removes what is >> effectively hardware support. If the maintenance cost exceeds the >> value, then removal is fair game. (Obviously we weight the value to >> preserving compatibility quite highly, but in this case, Xen dropped >> 32-bit hardware support a long time ago. If the Xen hypervisor says >> that 32-bit PV guest support is deprecated, it's deprecated.) >> >> That being said, a warning might not be a bad idea. What's the >> current status of this in upstream Xen? > > So personally, I'd prefer to see support stay, but at the end of the day > it is Juergen's choice as the maintainer of the code.
Especially on the security front we are unsafe with 32-bit PV Linux. And making it safe will make it so slow that the needed effort is not spent very well.
Juergen
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