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

[will.deacon@arm.com (Will Deacon)]

On Thu, Mar 08, 2018 at 01:54:26PM +0000, Ard Biesheuvel wrote:
> On 8 March 2018 at 13:49, Mark Rutland <mark.rutland@arm.com> wrote:
> > On Thu, Mar 08, 2018 at 01:46:34PM +0000, Ard Biesheuvel wrote:
> >> On 8 March 2018 at 13:45, Will Deacon <will.deacon@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.
> >
> > As with other case, perhaps fold this into a helper in
> > <asm/cpufeature.h> ?
> >
> > static inline bool system_needs_arm64_workaround_843419()
> > {
> >         return (IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) &&
> >                 cpus_have_const_cap(ARM64_WORKAROUND_843419))
> > }
> >
> > ... then use the inverse in the cases above.
> >
> 
> I'm fine with adding a helper, but
> 'system_needs_arm64_workaround_843419' is a bit misleading, given that
> it returns false if the system needs it but support is compiled out.

FWIW, I'm fine with the code as it is.

Will