linux-kernel - RE: Bogus struct page layout on 32-bit

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Date:   Sat, 17 Apr 2021 13:08:30 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Grygorii Strashko' <grygorii.strashko@...com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Christoph Hellwig <hch@....de>
CC:     Matthew Wilcox <willy@...radead.org>,
        kernel test robot <lkp@...el.com>,
        Linux-MM <linux-mm@...ck.org>,
        "kbuild-all@...ts.01.org" <kbuild-all@...ts.01.org>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        open list <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Matteo Croce <mcroce@...ux.microsoft.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: Bogus struct page layout on 32-bit

From: Grygorii Strashko
> Sent: 16 April 2021 10:27
...
> Sry, for delayed reply.
> 
> The TI platforms am3/4/5 (cpsw) and Keystone 2 (netcp) can do only 32bit DMA even in case of LPAE
> (dma-ranges are used).
> Originally, as I remember, CONFIG_ARCH_DMA_ADDR_T_64BIT has not been selected for the LPAE case
> on TI platforms and the fact that it became set is the result of multi-paltform/allXXXconfig/DMA
> optimizations and unification.
> (just checked - not set in 4.14)
> 
> Probable commit 4965a68780c5 ("arch: define the ARCH_DMA_ADDR_T_64BIT config symbol in lib/Kconfig").
> 
> The TI drivers have been updated, finally to accept ARCH_DMA_ADDR_T_64BIT=y by using things like
> (__force u32)
> for example.

Hmmm using (__force u32) is probably wrong.
If an address +length >= 2**32 can get passed then the IO request
needs to be errored (or a bounce buffer used).

Otherwise you can get particularly horrid corruptions.

	David

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