Re: [PATCH v4 04/26] arm64: alternative: Apply alternatives early in boot process

[Julien Thierry]

On 25/05/18 11:00, Suzuki K Poulose wrote:
> On 25/05/18 10:49, Julien Thierry wrote:
> > From: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> >
> > Currently alternatives are applied very late in the boot process (and
> > a long time after we enable scheduling). Some alternative sequences,
> > such as those that alter the way CPU context is stored, must be applied
> > much earlier in the boot sequence.
> >
> > Introduce apply_boot_alternatives() to allow some alternatives to be
> > applied immediately after we detect the CPU features of the boot CPU.
> >
> > Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> > [julien.thierry@xxxxxxx: rename to fit new cpufeature framework better,
> > ÂÂÂÂÂÂÂÂÂÂÂÂ apply BOOT_SCOPE feature early in boot]
> > Signed-off-by: Julien Thierry <julien.thierry@xxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> > Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> > Â arch/arm64/include/asm/alternative.h |Â 3 +--
> >  arch/arm64/include/asm/cpufeature.h | 2 ++
> > Â arch/arm64/kernel/alternative.cÂÂÂÂÂ | 30 
> > +++++++++++++++++++++++++++---
> > Â arch/arm64/kernel/cpufeature.cÂÂÂÂÂÂ |Â 5 +++++
> > Â arch/arm64/kernel/smp.cÂÂÂÂÂÂÂÂÂÂÂÂÂ |Â 7 +++++++
> > Â 5 files changed, 42 insertions(+), 5 deletions(-)
>
> ...
>
> > +unsigned long boot_capabilities;
> > +
> > Â /*
> > ÂÂ * Flag to indicate if we have computed the system wide
> > ÂÂ * capabilities based on the boot time active CPUs. This
> > @@ -1370,6 +1372,9 @@ static void __update_cpu_capabilities(const 
> > struct arm64_cpu_capabilities *caps,
> > ÂÂÂÂÂÂÂÂÂ if (!cpus_have_cap(caps->capability) && caps->desc)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ pr_info("%s %s\n", info, caps->desc);
> > ÂÂÂÂÂÂÂÂÂ cpus_set_cap(caps->capability);
> > +
> > +ÂÂÂÂÂÂÂ if (scope_mask & SCOPE_BOOT_CPU)
> > +ÂÂÂÂÂÂÂÂÂÂÂ __set_bit(caps->capability, &boot_capabilities);
>
> Julien
>
> I think this check is problematic. The scope_mask passed on by the boot CPU
> is (SCOPE_BOOT_CPU | SCOPE_LOCAL_CPU) to cover both BOOT CPU 
> capabilities *and*
> CPU local capabilites on the boot CPU. So, you might apply the 
> alternatives for
> a "local" CPU erratum, which is not intended. You may change the above 
> check to :
>
>  ÂÂÂÂif (caps->type & SCOPE_BOOT_CPU)
>
> to make sure you check the "capability" has the SCOPE_BOOT_CPU set.

Makes sense, I'll do that.

Thanks,

--
Julien Thierry