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

[Ard Biesheuvel]

On 23 February 2018 at 17:15, Mark Rutland <mark.rutland at arm.com> wrote:
> 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.
>

Instructions are always LE

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

Sure.