Re: [PATCH v4 1/3] cacheinfo: Add arch specific early level initializer

From: Sudeep Holla
Date: Mon May 15 2023 - 05:40:16 EST

On Wed, May 10, 2023 at 12:12:07PM -0700, Ricardo Neri wrote:
> Hi,
> I had posted a patchset[1] for x86 that initializes
> ci_cacheinfo(cpu)->num_leaves during SMP boot.

It is entirely clear to me if this is just a clean up or a fix to some
issue you faced ? Just wanted to let you know Prateek from AMD has couple
of fixes [2]

> This means that early_leaves and a late cache_leaves() are equal but
> per_cpu_cacheinfo(cpu) is never allocated. Currently, x86 does not use
> fetch_cache_info().
> I think that we should check here that per_cpu_cacheinfo() has been allocated to
> take care of the case in which early and late cache leaves remain the same:
> - if (cache_leaves(cpu) <= early_leaves)
> + if (cache_leaves(cpu) <= early_leaves && per_cpu_cacheinfo(cpu))
> Otherwise, in v6.4-rc1 + [1] I observe a NULL pointer dereference from
> last_level_cache_is_valid().

I think this is different issue as Prateek was just observing wrong info
after cpuhotplug operations. But the patches manage the cpumap_populated
state better with the patches. Can you please look at that as weel ?