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Message-ID: <20240911233410.GA7043@ranerica-svr.sc.intel.com>
Date: Wed, 11 Sep 2024 16:34:10 -0700
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
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 v6 2/4] cacheinfo: Allocate memory during CPU hotplug if
not done from the primary CPU
On Wed, Sep 11, 2024 at 04:08:44PM +0200, Borislav Petkov wrote:
> On Wed, Sep 04, 2024 at 11:00:34PM -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.
>
> Why is this a separate patch?
>
> It sounds like it should be merged with the first one as both address a CPU
> hotplug issue AFAICT.
Thank you for your review Borislav!
Yes, both patches address issues during CPU hotplug (both NULL-pointer
dereference). However, IHMO, they are separate issues. Patch 1/4 fixes
a missing allocation check. Patch 2/4 causes the allocation to happen in
case early allocation is not used.
If I did not convince you, I am happy to merge together patches 1 and 2.
Thanks and BR,
Ricardo
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