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: <20240829043719.GB4229@ranerica-svr.sc.intel.com>
Date: Wed, 28 Aug 2024 21:37:19 -0700
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Sudeep Holla <sudeep.holla@....com>
Cc: Nikolay Borisov <nik.borisov@...e.com>, 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>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Will Deacon <will@...nel.org>, Zhang Rui <rui.zhang@...el.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 Wed, Aug 28, 2024 at 02:57:19PM +0100, Sudeep Holla wrote:
> On Wed, Aug 28, 2024 at 04:16:00PM +0300, Nikolay Borisov wrote:
> > 
> > On 27.08.24 г. 8:16 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.
> > 
> > I assume instead of duplicating "memory" in the subject you meant
> > "cacheinfo" ?
> >
> 
> Good point, +1 for the $subject change. I clearly missed to notice that.

Ah! Yes, it should read cacheinfo: Allocate memory for cacheinfo if not done from the primary CPU.

Thanks for spotting the error. I will update the subject in the next version.

Thanks and BR,
Ricardo