>n Thu, Dec 12, 2024, at 17:27, Paolo Bonzini wrote:
> On 12/12/24 13:55, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@xxxxxxxx>
>>
>> There are very few 32-bit machines that support KVM, the main exceptions
>> are the "Yonah" Generation Xeon-LV and Core Duo from 2006 and the Atom
>> Z5xx "Silverthorne" from 2008 that were all released just before their
>> 64-bit counterparts.
>
> Unlike other architectures where you can't run a "short bitness" kernel
> at all, or 32-bit systems require hardware enablement that simply does
> not exist, the x86 situation is a bit different: 32-bit KVM would not be
> used on 32-bit processors, but on 64-bit kernels running 32-bit kernels;
> presumably on a machine with 4 or 8 GB of memory, above which you're
> hurting yourself even more, and for smaller guests where the limitations
> in userspace address space size don't matter.
>
> Apart from a bunch of CONFIG_X86_64 conditionals, the main issue that
> KVM has with 32-bit x86 is that they cannot read/write a PTE atomically
> (i.e. without tearing) and therefore they can't use the newer and more
> scalable page table management code. So no objections from me for
> removing this support, but the justification should be the truth, i.e.
> developers don't care enough.
Right, I should have updated the description based on the comments
for the first version, especially after separating it from the patches
that make it harder to run 32-bit kernels on 64-bit hardware.
I've updated the changelog now to
x86: kvm drop 32-bit host support
There are very few 32-bit machines that support KVM, the main exceptions
are the "Yonah" Generation Xeon-LV and Core Duo from 2006 and the Atom
Z5xx "Silverthorne" from 2008 that were all released just before their
64-bit counterparts.
The main usecase for KVM in x86-32 kernels these days is to verify
that 32-bit KVM is still working, by running it on 64-bit hardware.
With KVM support on other 32-bit architectures going away, and x86-32
kernels on 64-bit hardware becoming more limited in available RAM,
this usecase becomes much less interesting.
Remove this support to make KVM exclusive to 64-bit hosts on all
architectures, and stop testing 32-bit host mode.
Link: https://lore.kernel.org/all/Z1B1phcpbiYWLgCD@xxxxxxxxxx/
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
which assumes that we end up going ahead with the powerpc
patches. Does that work for you?
Arnd
