On 08.02.24 07:10, Mike Rapoport wrote:

On Mon, Jan 29, 2024 at 01:46:35PM +0100, David Hildenbrand wrote:

quoted

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/ (local)
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: David Hildenbrand <redacted>
Signed-off-by: David Hildenbrand <redacted>

Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>

Thanks for the review Mike, appreciated!

-- 
Cheers,

David / dhildenb


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