Re: [PATCH v3 06/23] kvm: arm64: Add kvm-arm.protected early kernel parameter

David Brazdil
2020-12-01T14:45:07Z

> > > be just me, but if you agree please update so that it doesn't give remote
> > > idea that it is not valid on VHE enabled hardware.
> > >
> > > I was trying to run this on the hardware and was trying to understand the
> > > details on how to do that.
> >
> > I see what you're saying, but !CONFIG_ARM64_VHE isn't accurate either. The
> > option makes sense if:
> > 1) all cores booted in EL2
> > == is_hyp_mode_available()
> > 2) ID_AA64MMFR1_EL1.VH=0 or !CONFIG_ARM64_VHE
> > == !is_kernel_in_hyp_mode()
> >
> > The former feels implied for KVM, the latter could be 'Valid if the kernel
> > is running in EL1'? WDYT?
>
> I reckon we can avoid the restriction if we instead add an early stub
> like with have for KASLR. That way we could parse the command line
> early, and if necessary re-initialize EL2 and drop to EL1 before the
> main kernel has to make any decisions about how to initialize things.
> That would allow us to have a more general kvm-arm.mode option where a
> single kernel Image could support:
>
> * "protected" mode on nVHE or VHE HW
> * "nvhe" mode on nVHE or VHE HW
> * "vhe" mode on VHE HW
>
> ... defaulting to VHE/nVHE modes depending on HW support.
>
> That would also be somewhat future-proof if we have to add other
> variants of protected mode in future, as we could extend the mode option
> with parameters for each mode.

Agreed that 'mode' is a more future-proof flag and I would very much love to
have an option to force nVHE on VHE HW. I however expect that the early stub
would not be a trivial addition and would not want to get into that in this
series. Could we agree on 'protected' as the only supported value for the time
being?

David