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Date:   Wed, 9 Aug 2023 19:05:04 +0200
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Subject: Re: [PATCH] arm: dma-mapping: fix potential endless loop in
 __dma_page_dev_to_cpu()
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To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Russell King <linux@armlinux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@kernel.org>
From:   Marek Szyprowski <m.szyprowski@samsung.com>
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        <20230807152657.1692414-1-m.szyprowski@samsung.com>
        <ZNEagJ6rVDwBKUdr@casper.infradead.org>
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Hi,

On 07.08.2023 18:23, Matthew Wilcox wrote:
> On Mon, Aug 07, 2023 at 05:26:57PM +0200, Marek Szyprowski wrote:
>> It is possible that the folio_size() of the next folio returns zero, so
> What?  How can folio_size() return zero?
>
>          return PAGE_SIZE << folio_order(folio);
>
> It is a minimum of PAGE_SIZE.

Well, the folio_order() on that next folio returns 255, so folio_size() 
overflows to zero. However, the main source of this issue is relying on 
the properties of the folio beyond the requested sync region.

 > ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland