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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: stable <stable@vger.kernel.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Matteo Croce <mcroce@linux.microsoft.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: fix struct page layout on 32-bit systems
Date: Sun, 16 May 2021 12:22:43 -0700	[thread overview]
Message-ID: <CAHk-=wj6RAF5OFq3Pp725e0BFU2e0QnMCvhfF_3TBhk=UqN3Jw@mail.gmail.com> (raw)
In-Reply-To: <YKFt4Njj5au/JEhT@casper.infradead.org>

On Sun, May 16, 2021 at 12:09 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> That was the other problem fixed by this patch -- on big-endian 32-bit
> platforms with 64-bit dma_addr_t (mips, ppc), a DMA address with bit 32 set
> inadvertently sets the PageTail bit.  So we need to store the low bits
> in the first word, even on big-endian platforms.

Ouch. And yes, that would have shot down the "dma page frame number" model too.

Oh how I wish PageTail was in "flags". Yes, our compound_head() thing
is "clever", but it's a pain,

That said, that union entry is "5 words", so the dma_addr_t thing
could easily just have had a dummy word at the beginning.

          Linus

  reply	other threads:[~2021-05-16 19:23 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-16 12:18 [PATCH] mm: fix struct page layout on 32-bit systems Matthew Wilcox (Oracle)
2021-05-16 12:31 ` Matthew Wilcox
2021-05-17 10:06   ` Greg KH
2021-05-16 16:29 ` Linus Torvalds
2021-05-16 18:22   ` Matthew Wilcox
2021-05-16 18:27     ` Linus Torvalds
2021-05-16 19:09       ` Matthew Wilcox
2021-05-16 19:22         ` Linus Torvalds [this message]
2021-05-17  2:42           ` Matthew Wilcox
2021-05-17 22:18             ` Linus Torvalds
2021-05-17 23:02               ` Matthew Wilcox
2021-05-17 23:37                 ` Linus Torvalds
2021-05-18  0:02                   ` Linus Torvalds
2021-05-18  0:53                     ` Matthew Wilcox
  -- strict thread matches above, loose matches on Subject: below --
2021-05-10 15:32 [PATCH] mm: Fix " Matthew Wilcox (Oracle)
2021-05-10 16:38 ` Matteo Croce

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