On Tue, Jan 23, 2018 at 12:27:59PM +0000, Suzuki K Poulose wrote:
> Now that each capability describes how to treat the conflicts
> of CPU cap state vs System wide cap state, we can unify the
> verification logic to a single place.
>
> Signed-off-by: Suzuki K Poulose <[email protected]>
> ---
> arch/arm64/kernel/cpufeature.c | 87
> ++++++++++++++++++++++++++----------------
> 1 file changed, 54 insertions(+), 33 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 43c7e992d784..79737034a628 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1228,6 +1228,54 @@ static void __init enable_cpu_capabilities(const
> struct arm64_cpu_capabilities *
> }
>
> /*
> + * Run through the list of capabilities to check for conflicts.
> + * Returns "false" on conflicts.
> + */
> +static bool __verify_local_cpu_caps(const struct arm64_cpu_capabilities
> *caps_list)
> +{
> + bool cpu_has_cap, system_has_cap;
> + const struct arm64_cpu_capabilities *caps = caps_list;
> +
> + for (; caps->matches; caps++) {
> + cpu_has_cap = __this_cpu_has_cap(caps_list, caps->capability);
What's the point of scanning the whole of caps_list? Don't we already
have the pointer to the right cap struct?
We already know caps->matches is true. Can't we just call
caps->matches(caps)? That seemed pretty intuitive to me in the old
code.
> + system_has_cap = cpus_have_cap(caps->capability);
> +
> + if (system_has_cap) {
> + /*
> + * Check if the new CPU misses an advertised feature,
> which is not
> + * safe to miss.
> + */
> + if (!cpu_has_cap &&
> !cpucap_late_cpu_missing_cap_safe(caps))
> + break;
> + /*
> + * We have to issue enable() irrespective of whether
> the CPU
> + * has it or not, as it is enabeld system wide. It is
> upto
enabled
> + * the call back to take appropriate action on this CPU.
> + */
> + if (caps->enable)
> + caps->enable(caps);
> + } else {
> + /*
> + * Check if the CPU has this capability if it isn't
> safe to
> + * have when the system doesn't.
> + */
Possibly most of the commenting here is not needed. The code is pretty
self-explanatory, so the comments may just be adding clutter.
The role of the ->enable() call is the only real subtlety here.
> + if (cpu_has_cap && !cpucap_late_cpu_have_cap_safe(caps))
> + break;
> + }
> + }
> +
> + if (caps->matches) {
> + pr_crit("CPU%d: Detected conflict for capability %d (%s),
> System: %d, CPU: %d\n",
> + smp_processor_id(), caps->capability,
> + caps->desc ? : "no description",
Wouldn't it be a bug for a conflict to occur on a cap with no .desc?
Why can't we just let printk print its default "(null)" for %s
in this case?
Alternatively, is there a reason for any cap not to have a description?
> + system_has_cap, cpu_has_cap);
> + return false;
> + }
> +
> + return true;
> +}
Perhaps the capability verification procedure could be made a little
clearer by splitting this into two functions:
static bool __verify_local_cpu_cap(const struct arm64_cpu_capabilities *cap)
{
bool cpu_has_cap = cap->matches(cap, SCOPE_LOCAL_CPU);
bool system_has_cap = cpus_have_cap(cap->capability);
if (system_has_cap) {
if (!cpu_has_cap && !cpucap_late_cpu_missing_cap_safe(cap))
goto bad;
if (cap->enable)
/* Enable for this cpu if appropriate: */
cap->enable(cap);
} else {
if (cpu_has_cap && !cpucap_late_cpu_have_cap_safe(cap))
goto bad;
}
return true;
bad:
pr_crit([...]);
return false;
}
static bool __verify_local_cpu_caps(const struct arm64_cpu_capabilities *caps)
{
while (caps->matches) {
if (!__verify_local_cpu_cap(caps))
return false;
++caps;
}
return true;
}
[...]
Cheers
---Dave
