[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 17:25, Mark Rutland <mark.rutland at arm.com> wrote:
> On Fri, Feb 23, 2018 at 05:17:31PM +0000, Ard Biesheuvel wrote:
>> 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
>
> Ugh; I forgot that single didn't have endianness. :(
>
>> > Can we not construct the equivalent ADR using the usual insn code, and
>> > insert it?
>>
>> Sure.
>
> Cheers!
>

Umm, it appears we don't have any code to emit ADR or ADRP
instructions, and I am reluctant to add a bunch of routines that are
only ever used to flick a single opcode bit.