[PATCH v4 5/5] arm64/kernel: enable A53 erratum #8434319 handling at runtime

[Ard Biesheuvel]

On 8 March 2018 at 13:46, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> On 8 March 2018 at 13:45, Will Deacon <will.deacon at arm.com> wrote:
>> On Tue, Mar 06, 2018 at 05:15:35PM +0000, Ard Biesheuvel wrote:
>>> Omit patching of ADRP instruction at module load time if the current
>>> CPUs are not susceptible to the erratum.
>>
>> [...]
>>
>>> diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
>>> index 534bf1d47119..1a583ccace00 100644
>>> --- a/arch/arm64/kernel/module-plts.c
>>> +++ b/arch/arm64/kernel/module-plts.c
>>> @@ -158,7 +158,8 @@ static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num,
>>>                       break;
>>>               case R_AARCH64_ADR_PREL_PG_HI21_NC:
>>>               case R_AARCH64_ADR_PREL_PG_HI21:
>>> -                     if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_843419))
>>> +                     if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) ||
>>> +                         !cpus_have_const_cap(ARM64_WORKAROUND_843419))
>>>                               break;
>>>
>>>                       /*
>>> diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
>>> index 89217704944e..47b40aaa1a5d 100644
>>> --- a/arch/arm64/kernel/module.c
>>> +++ b/arch/arm64/kernel/module.c
>>> @@ -201,6 +201,7 @@ static int reloc_insn_imm(enum aarch64_reloc_op op, __le32 *place, u64 val,
>>>  static int reloc_insn_adrp(struct module *mod, __le32 *place, u64 val)
>>>  {
>>>       if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) ||
>>> +         !cpus_have_const_cap(ARM64_WORKAROUND_843419) ||
>>
>> Mind if I drop the IS_ENABLED check here and in the hunk above? The
>> const_cap check along should be sufficient, no?
>>
>
> Without the IS_ENABLED() check, the code will always be present in the
> object file.
>
> I have no strong preference either way, though.

Ehm, strike that. You will probably hit a linker error if you drop it,
because some dependent functions are #ifdef'ed out if the erratum
workaround is disabled.