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Date: Fri, 9 Feb 2024 23:36:17 +0100
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Subject: Re: [PATCH v3 01/15] arm64/mm: Make set_ptes() robust when OAs cross
 48-bit boundary
To: Mike Rapoport <rppt@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
 Andrew Morton <akpm@linux-foundation.org>,
 Matthew Wilcox <willy@infradead.org>, Ryan Roberts <ryan.roberts@arm.com>,
 Russell King <linux@armlinux.org.uk>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 Dinh Nguyen <dinguyen@kernel.org>, Michael Ellerman <mpe@ellerman.id.au>,
 Nicholas Piggin <npiggin@gmail.com>,
 Christophe Leroy <christophe.leroy@csgroup.eu>,
 "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>,
 "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
 Paul Walmsley <paul.walmsley@sifive.com>, Palmer Dabbelt
 <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>,
 Alexander Gordeev <agordeev@linux.ibm.com>,
 Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
 Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>,
 Christian Borntraeger <borntraeger@linux.ibm.com>,
 Sven Schnelle <svens@linux.ibm.com>, "David S. Miller"
 <davem@davemloft.net>, linux-arm-kernel@lists.infradead.org,
 linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
 linux-s390@vger.kernel.org, sparclinux@vger.kernel.org
References: <20240129124649.189745-1-david@redhat.com>
 <20240129124649.189745-2-david@redhat.com> <ZcRwc2mEDHIXxgGa@kernel.org>
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From: David Hildenbrand <david@redhat.com>
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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@arm.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@arm.com>
>> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>

Thanks for the review Mike, appreciated!

-- 
Cheers,

David / dhildenb