linux-kernel - Re: [PATCH v3 01/15] arm64/mm: Make set_ptes() robust when OAs cross 48-bit boundary

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Date: Fri, 9 Feb 2024 23:36:17 +0100
From: David Hildenbrand <david@...hat.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>, Ryan Roberts <ryan.roberts@....com>,
 Russell King <linux@...linux.org.uk>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Dinh Nguyen <dinguyen@...nel.org>, Michael Ellerman <mpe@...erman.id.au>,
 Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, "David S. Miller"
 <davem@...emloft.net>, linux-arm-kernel@...ts.infradead.org,
 linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
 linux-s390@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v3 01/15] arm64/mm: Make set_ptes() robust when OAs cross
 48-bit boundary

On 08.02.24 07:10, Mike Rapoport wrote:
> On Mon, Jan 29, 2024 at 01:46:35PM +0100, David Hildenbrand wrote:
>> From: Ryan Roberts <ryan.roberts@....com>
>>
>> Since the high bits [51:48] of an OA are not stored contiguously in the
>> PTE, there is a theoretical bug in set_ptes(), which just adds PAGE_SIZE
>> to the pte to get the pte with the next pfn. This works until the pfn
>> crosses the 48-bit boundary, at which point we overflow into the upper
>> attributes.
>>
>> Of course one could argue (and Matthew Wilcox has :) that we will never
>> see a folio cross this boundary because we only allow naturally aligned
>> power-of-2 allocation, so this would require a half-petabyte folio. So
>> its only a theoretical bug. But its better that the code is robust
>> regardless.
>>
>> I've implemented pte_next_pfn() as part of the fix, which is an opt-in
>> core-mm interface. So that is now available to the core-mm, which will
>> be needed shortly to support forthcoming fork()-batching optimizations.
>>
>> Link: https://lkml.kernel.org/r/20240125173534.1659317-1-ryan.roberts@arm.com
>> Fixes: 4a169d61c2ed ("arm64: implement the new page table range API")
>> Closes: https://lore.kernel.org/linux-mm/fdaeb9a5-d890-499a-92c8-d171df43ad01@arm.com/
>> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
>> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
>> Reviewed-by: David Hildenbrand <david@...hat.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
> 
> Reviewed-by: Mike Rapoport (IBM) <rppt@...nel.org>

Thanks for the review Mike, appreciated!

-- 
Cheers,

David / dhildenb