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

[Alexandru Elisei]

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.

Thanks,
Alex

> 
> Anyway, I've applied this to fixes.
> 
> Thanks,
> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.