linux-kernel - Re: [PATCH v1 1/4] mm/memory_hotplug: use "unsigned long" for PFN in zone_for_pfn

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Message-ID: <99c59db8-4c3d-6bee-9acc-41a8f76899ef@redhat.com>
Date:   Thu, 15 Jul 2021 11:42:21 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Heiko Carstens <hca@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Catalin Marinas <catalin.marinas@....com>,
        virtualization@...ts.linux-foundation.org,
        linux-acpi@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anton Blanchard <anton@...abs.org>,
        Ard Biesheuvel <ardb@...nel.org>, Baoquan He <bhe@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
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        Sergei Trofimovich <slyfox@...too.org>,
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        Vishal Verma <vishal.l.verma@...el.com>,
        Will Deacon <will@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH v1 1/4] mm/memory_hotplug: use "unsigned long" for PFN in
 zone_for_pfn_range()

On 14.07.21 22:13, Heiko Carstens wrote:
> On Mon, Jul 12, 2021 at 02:40:49PM +0200, David Hildenbrand wrote:
>> Checkpatch complained on a follow-up patch that we are using "unsigned"
>> here, which defaults to "unsigned int" and checkpatch is correct.
>>
>> Use "unsigned long" instead, just as we do in other places when handling
>> PFNs. This can bite us once we have physical addresses in the range of
>> multiple TB.
>>
>> Fixes: e5e689302633 ("mm, memory_hotplug: display allowed zones in the preferred ordering")
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>   include/linux/memory_hotplug.h | 4 ++--
>>   mm/memory_hotplug.c            | 4 ++--
>>   2 files changed, 4 insertions(+), 4 deletions(-)
> 
> I'd propose to add Cc: <stable@...r.kernel.org> since I actually had
> the fun to try to debug something like this a couple of years ago:
> 6cdb18ad98a4 ("mm/vmstat: fix overflow in mod_zone_page_state()")
> 

Good point, and thinking again what can go wrong, I tend to agree. We 
are trying to keep zones contiguous and it could happen that we end up 
with something like ZONE_DMA here (via default_kernel_zone_for_pfn()) 
and would consequently online something to ZONE_DMA that doesn't belong 
there, resulting in crashes.

@Andrew can you add  Cc: <stable@...r.kernel.org> and

"As we will search for a fitting zone using the wrong pfn, we might end 
up onlining memory to one of the special kernel zones, such as ZONE_DMA, 
which can end badly as the onlined memory does not satisfy properties of 
these zones."

Thanks Heiko!

-- 
Thanks,

David / dhildenb