[PATCH v2 0/2] KVM: arm64: Uphold 64bit-only behavior on asymmetric systems

[Marc Zyngier]

On Wed, 17 Aug 2022 11:52:06 +0100,
Alexandru Elisei <alexandru.elisei at arm.com> wrote:
> 
> Hi,
> 
> On Wed, Aug 17, 2022 at 11:07:10AM +0100, Marc Zyngier wrote:
> > On Tue, 16 Aug 2022 20:25:52 +0100,
> > Oliver Upton <oliver.upton at linux.dev> wrote:
> > > 
> > > Small series to fix a couple issues around when 64bit-only behavior is
> > > applied. As KVM is more restrictive than the kernel in terms of 32bit
> > > support (no asymmetry), we really needed our own predicate when the
> > > meaning of system_supports_32bit_el0() changed in commit 2122a833316f
> > > ("arm64: Allow mismatched 32-bit EL0 support").
> > > 
> > > Lightly tested as I do not have any asymmetric systems on hand at the
> > > moment. Attention on patch 2 would be appreciated as it affects ABI.
> > 
> > I don't think this significantly affect the ABI, as it is pretty
> > unlikely that you'd have been able to execute the result, at least on
> > VM creation (set PSTATE.M=USR, start executing, get the page fault on
> > the first instruction... bang).
> > 
> > You could have tricked it in other ways, but at the end of the day
> > you're running a broken hypervisor on an even more broken system...
> 
> Just FYI, you can create such a system on models, by running two clusters
> and setting clusterX.max_32bit_el=-1. Or you can have even crazier
> configurations, where AArch32 support is present on only one cluster, and
> only for EL0.

You mean, just as crazy as some of the systems out there? :D

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.