Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier <maz@kernel.org>]

On Fri, 01 Oct 2021 10:27:18 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> On 30/09/2021 11:29, Marc Zyngier wrote:
> > On Wed, 29 Sep 2021 11:35:46 +0100,
> > Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> >> 
> >>> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> >> 
> >> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> >> user wants to keep the KVM out of the picture for, say debugging
> >> something, it is perfectly Ok to allow the kernel to be running at EL2
> >> without having to change the Firmware to alter the landing EL for the
> >> kernel ?
> > 
> > Well, the doc says "run in nVHE mode" and the option forces
> > id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> > that is VHE only. Note that this doesn't rely on any firmware change
> > (we drop from EL2 to EL1 and stay there).
> 
> Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
> missed. TBH, that name to me sounds like "no KVM" at all, which is what
> we want. The question is, do we really need "none" to force vh == 0 ? I
> understand this is only a problem on a rare set of HWs. But the generic
> option looks deceiving.
> 
> That said, I am happy to leave this as is and the doc says so.

I think you have a point here. Conflating the two things is a bit odd,
and we might as well let the user pick the configuration they want
(they can always pass 'id_aa64mmfr1.vh=0' themselves).

I'll respin the patch with this change.

Thanks,

	M.

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