From: David Laight <David.Laight@ACULAB.COM>
To: 'Matthew Wilcox' <willy@infradead.org>,
Jesper Dangaard Brouer <brouer@redhat.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
Ilias Apalodimas <ilias.apalodimas@linaro.org>,
Matteo Croce <mcroce@linux.microsoft.com>,
Grygorii Strashko <grygorii.strashko@ti.com>,
Arnd Bergmann <arnd@kernel.org>, "Christoph Hellwig" <hch@lst.de>
Subject: RE: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems
Date: Thu, 15 Apr 2021 21:11:56 +0000 [thread overview]
Message-ID: <5179a01a462f43d6951a65de2a299070@AcuMS.aculab.com> (raw)
In-Reply-To: <20210415182155.GD2531743@casper.infradead.org>
From: Matthew Wilcox <willy@infradead.org>
> Sent: 15 April 2021 19:22
>
> On Thu, Apr 15, 2021 at 08:08:32PM +0200, Jesper Dangaard Brouer wrote:
> > +static inline
> > +dma_addr_t page_pool_dma_addr_read(dma_addr_t dma_addr)
> > +{
> > + /* Workaround for storing 64-bit DMA-addr on 32-bit machines in struct
> > + * page. The page->dma_addr share area with page->compound_head which
> > + * use bit zero to mark compound pages. This is okay, as DMA-addr are
> > + * aligned pointers which have bit zero cleared.
> > + *
> > + * In the 32-bit case, page->compound_head is 32-bit. Thus, when
> > + * dma_addr_t is 64-bit it will be located in top 32-bit. Solve by
> > + * swapping dma_addr 32-bit segments.
> > + */
> > +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
>
> #if defined(CONFIG_ARCH_DMA_ADDR_T_64BIT) && defined(__BIG_ENDIAN)
> otherwise you'll create the problem on ARM that you're avoiding on PPC ...
>
> I think you want to delete the word '_read' from this function name because
> you're using it for both read and write.
I think I'd use explicit dma_addr_hi and dma_addr_lo and
separate read/write functions just to make absolutely sure
nothing picks up the swapped value.
Isn't it possible to move the field down one long?
This might require an explicit zero - but this is not a common
code path - the extra write will be noise.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-04-15 21:12 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-10 20:52 [PATCH 0/1] Fix struct page layout on 32-bit systems Matthew Wilcox (Oracle)
2021-04-10 20:52 ` [PATCH 1/1] mm: " Matthew Wilcox (Oracle)
2021-04-11 9:43 ` Jesper Dangaard Brouer
2021-04-11 10:33 ` Matthew Wilcox
2021-04-12 1:15 ` Matthew Wilcox
2021-04-14 8:10 ` Jesper Dangaard Brouer
2021-04-14 11:50 ` Matthew Wilcox
2021-04-14 11:56 ` Ilias Apalodimas
2021-04-14 15:52 ` David Laight
2021-04-14 19:13 ` Jesper Dangaard Brouer
2021-04-14 21:35 ` Matthew Wilcox
2021-04-14 21:56 ` David Laight
2021-04-15 18:08 ` Jesper Dangaard Brouer
2021-04-15 18:21 ` Matthew Wilcox
2021-04-15 21:11 ` David Laight [this message]
2021-04-15 22:22 ` Matthew Wilcox
2021-04-16 7:32 ` David Laight
2021-04-16 11:05 ` Matthew Wilcox
2021-04-16 15:27 ` Matthew Wilcox
2021-04-16 17:08 ` Jesper Dangaard Brouer
2021-04-17 3:19 ` Matthew Wilcox
2021-04-17 10:31 ` Arnd Bergmann
2021-04-17 13:56 ` Matthew Wilcox
2021-04-17 17:30 ` Arnd Bergmann
2021-04-17 10:59 ` David Laight
2021-04-19 6:34 ` Christoph Hellwig
2021-04-19 7:15 ` Ilias Apalodimas
2021-04-12 18:23 ` Matthew Wilcox
2021-04-13 8:21 ` David Laight
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