Re: [PATCH v8 1/2] cacheinfo: Allocate memory during CPU hotplug if not done from the primary CPU

[Nikolay Borisov]

On 28.11.24 г. 2:22 ч., Ricardo Neri wrote:
> Commit 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")
> adds functionality that architectures can use to optionally allocate and
> build cacheinfo early during boot. Commit 6539cffa9495 ("cacheinfo: Add
> arch specific early level initializer") lets secondary CPUs correct (and
> reallocate memory) cacheinfo data if needed.
>
> If the early build functionality is not used and cacheinfo does not need
> correction, memory for cacheinfo is never allocated. x86 does not use the
> early build functionality. Consequently, during the cacheinfo CPU hotplug
> callback, last_level_cache_is_valid() attempts to dereference a NULL
> pointer:
>
>       BUG: kernel NULL pointer dereference, address: 0000000000000100
>       #PF: supervisor read access in kernel mode
>       #PF: error_code(0x0000) - not present page
>       PGD 0 P4D 0
>       Oops: 0000 [#1] PREEPMT SMP NOPTI
>       CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1
>       RIP: 0010: last_level_cache_is_valid+0x95/0xe0a
>
> Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback if
> not done earlier.
>
> Moreover, before determining the validity of the last-level cache info,
> ensure that it has been allocated. Simply checking for non-zero
> cache_leaves() is not sufficient, as some architectures (e.g., Intel
> processors) have non-zero cache_leaves() before allocation.
>
> Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size().
> This function iterates over all online CPUs. However, a CPU may have come
> online recently, but its cacheinfo may not have been allocated yet.
>
> While here, remove an unnecessary indentation in allocate_cache_info().
>
> Reviewed-by: Andreas Herrmann <aherrmann@xxxxxxx>
> Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
> Reviewed-by: Radu Rendec <rrendec@xxxxxxxxxx>
> Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> Tested-by: Andreas Herrmann <aherrmann@xxxxxxx>
> Fixes: 6539cffa9495 ("cacheinfo: Add arch specific early level initializer")
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>


Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>