linux-kernel - Re: [PATCH] powerpc: Perform a bounds check in arch_add

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Date:   Tue, 27 Aug 2019 09:18:21 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Alastair D'Silva <alastair@....ibm.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: Perform a bounds check in arch_add_memory

On Tue 27-08-19 16:39:56, Alastair D'Silva wrote:
> On Tue, 2019-08-27 at 08:28 +0200, Michal Hocko wrote:
> > On Tue 27-08-19 15:20:46, Alastair D'Silva wrote:
> > > From: Alastair D'Silva <alastair@...ilva.org>
> > > 
> > > It is possible for firmware to allocate memory ranges outside
> > > the range of physical memory that we support (MAX_PHYSMEM_BITS).
> > 
> > Doesn't that count as a FW bug? Do you have any evidence of that in
> > the
> > field? Just wondering...
> > 
> 
> Not outside our lab, but OpenCAPI attached LPC memory is assigned
> addresses based on the slot/NPU it is connected to. These addresses
> prior to:
> 4ffe713b7587 ("powerpc/mm: Increase the max addressable memory to 2PB")
> were inaccessible and resulted in bogus sections - see our discussion
> on 'mm: Trigger bug on if a section is not found in __section_nr'.

Please document this in the changelog

-- 
Michal Hocko
SUSE Labs