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

Catalin Marinas
2021-01-23T14:09:06Z

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.

--
Catalin