linux-kernel - Re: [PATCH v5 2/4] cacheinfo: Allocate memory for memory if not done from the primary CPU

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Message-ID: <20240901180807.GB4089@alberich>
Date: Sun, 1 Sep 2024 20:08:07 +0200
From: Andreas Herrmann <aherrmann@...e.de>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: x86@...nel.org, Andreas Herrmann <aherrmann@...e.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Chen Yu <yu.c.chen@...el.com>, Len Brown <len.brown@...el.com>,
	Radu Rendec <rrendec@...hat.com>,
	Pierre Gondois <Pierre.Gondois@....com>, Pu Wen <puwen@...on.cn>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Sudeep Holla <sudeep.holla@....com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Will Deacon <will@...nel.org>, Zhang Rui <rui.zhang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Huang Ying <ying.huang@...el.com>,
	Ricardo Neri <ricardo.neri@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/4] cacheinfo: Allocate memory for memory if not done
 from the primary CPU

On Mon, Aug 26, 2024 at 10:16:33PM -0700, 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.
> 
> Reviewed-by: Radu Rendec <rrendec@...hat.com>
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> Fixes: 6539cffa9495 ("cacheinfo: Add arch specific early level initializer")
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>

Reviewed-by: Andreas Herrmann <aherrmann@...e.de>
Tested-by: Andreas Herrmann <aherrmann@...e.de>

Test was done with a system equipped with AMD Phenom II X6 1055T and
test kernels based on v6.11-rc5-176-g20371ba12063.


Thanks,
Andreas