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Re: [Xen-devel] [PATCH 0/2] Remove 32-bit Xen PV guest support
- To: Andy Lutomirski <luto@xxxxxxxxxx>
- From: Jan Beulich <JBeulich@xxxxxxxx>
- Date: Tue, 16 Jul 2019 06:58:14 +0000
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- Cc: Juergen Gross <JGross@xxxxxxxx>, Andi Kleen <ak@xxxxxxxxxxxxxxx>, X86 ML <x86@xxxxxxxxxx>, Alok Kataria <akataria@xxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Delivery-date: Tue, 16 Jul 2019 06:59:30 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHVOyspJT4e/CSPYU+qON3EVGWuQqbL7231gADh4YA=
- Thread-topic: [Xen-devel] [PATCH 0/2] Remove 32-bit Xen PV guest support
On 15.07.2019 19:28, Andy Lutomirski wrote:
> On Mon, Jul 15, 2019 at 9:34 AM Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote:
>>
>> Juergen Gross <jgross@xxxxxxxx> 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.)
Since it was implied but not explicit from Andrew's reply, just to
make it explicit: So far 32-bit PV guest support has not been
deprecated in Xen itself.
Jan
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