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

On Mon, May 15, 2023 at 10:36:08AM +0100, Sudeep Holla wrote:

On Wed, May 10, 2023 at 12:12:07PM -0700, Ricardo Neri wrote:

quoted

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]

My first patch is a bug fix. The second patch is clean up that results
from fixing the bug in patch 1.

quoted

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 ?

I verified that the patches from Prateek fix a different issue. I was able
to reproduce his issue. His patches fixes it.

I still see my issue after applying Prateek's patches.

-- 
Regards,
Sudeep

[2] https://lore.kernel.org/all/20230508084115.1157-1-kprateek.nayak@amd.com (local)

Thank you for the suggestion!

BR,
Ricardo

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