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

[Will Deacon]

On Thu, Mar 08, 2018 at 01:47:26PM +0000, Ard Biesheuvel wrote:
> 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.

Ah, ok then. Thanks for the quick response.

Will