[RFC PATCH v3 2/3] arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum #843419

[Mark Rutland]

On Wed, Feb 14, 2018 at 11:36:44AM +0000, Ard Biesheuvel wrote:
> +static bool reloc_adrp_erratum_843419(struct module *mod, __le32 *place,
> +				      u64 val)
> +{
> +	if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_843419))
> +		return false;
> +
> +	/* only ADRP instructions at the end of a 4k page are affected */
> +	if (((u64)place & 0xfff) < 0xff8)
> +		return false;
> +
> +	/* patch ADRP to ADR if it is in range */
> +	if (!reloc_insn_imm(RELOC_OP_PREL, place, val & ~0xfff, 0, 21,
> +			    AARCH64_INSN_IMM_ADR)) {
> +		((u8 *)place)[3] &= 0x7f; /* clear opcode bit 31 */

That's a bit hideous, and broken for BE, I think.

Can we not construct the equivalent ADR using the usual insn code, and
insert it?

Thanks,
Mark.