Re: [PATCH v4 14/21] arm64: Honor VHE being disabled from the command-line

Marc Zyngier
2021-01-24T16:01:03Z

On Sat, 23 Jan 2021 14:07:53 +0000,
Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Mon, Jan 18, 2021 at 09:45:26AM +0000, Marc Zyngier wrote:
> > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> > index 59820f9b8522..bbab2148a2a2 100644
> > --- a/arch/arm64/kernel/hyp-stub.S
> > +++ b/arch/arm64/kernel/hyp-stub.S
> > @@ -77,13 +77,24 @@ SYM_CODE_END(el1_sync)
> > SYM_CODE_START_LOCAL(mutate_to_vhe)
> > // Sanity check: MMU *must* be off
> > mrs x0, sctlr_el2
> > - tbnz x0, #0, 1f
> > + tbnz x0, #0, 2f
> >
> > // Needs to be VHE capable, obviously
> > mrs x0, id_aa64mmfr1_el1
> > ubfx x0, x0, #ID_AA64MMFR1_VHE_SHIFT, #4
> > - cbz x0, 1f
> > + cbz x0, 2f
> >
> > + // Check whether VHE is disabled from the command line
> > + adr_l x1, id_aa64mmfr1_val
> > + ldr x0, [x1]
> > + adr_l x1, id_aa64mmfr1_mask
> > + ldr x1, [x1]
> > + ubfx x0, x0, #ID_AA64MMFR1_VHE_SHIFT, #4
> > + ubfx x1, x1, #ID_AA64MMFR1_VHE_SHIFT, #4
> > + cbz x1, 1f
> > + and x0, x0, x1
> > + cbz x0, 2f
> > +1:
>
> I can see the advantage here in separate id_aa64mmfr1_val/mask but we
> could use some asm offsets here and keep the pointer indirection simpler
> in C code. You'd just need something like 'adr_l mmfr1_ovrd + VAL_OFFSET'.
>
> Anyway, if you have a strong preference for the current approach, leave
> it as is.

I've now moved over to a structure containing both val/mask, meaning
that we only need to keep a single pointer around in the various
feature descriptors. It certainly looks better.

Thanks,

M.

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