From: catalin.marinas@arm•com (Catalin Marinas)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] arm64: Correct virt_addr_valid
Date: Thu, 12 Dec 2013 17:57:54 +0000 [thread overview]
Message-ID: <20131212175753.GG3382@arm.com> (raw)
In-Reply-To: <20131211211333.GI4360@n2100.arm.linux.org.uk>
On Wed, Dec 11, 2013 at 09:13:33PM +0000, Russell King - ARM Linux wrote:
> There is actually a concern here, and that's if the v:p translation isn't
> linear, could it return false results?
>
> According to my grep skills, we have one platform where this is true -
> Realview:
>
> * 256MB @ 0x00000000 -> PAGE_OFFSET
> * 512MB @ 0x20000000 -> PAGE_OFFSET + 0x10000000
> * 256MB @ 0x80000000 -> PAGE_OFFSET + 0x30000000
>
> The v:p translation is done via:
>
> ((virt) >= PAGE_OFFSET2 ? (virt) - PAGE_OFFSET2 + 0x80000000 : \
> (virt) >= PAGE_OFFSET1 ? (virt) - PAGE_OFFSET1 + 0x20000000 : \
> (virt) - PAGE_OFFSET)
>
> Now the questions - what do values below PAGE_OFFSET give us? Very
> large numbers, which pfn_valid() should return false for. What about
> values > PAGE_OFFSET2 + 256MB? The same.
>
> So this all _looks_ fine. Wait a moment, what about highmem? Let's say
> that the last 256MB is only available as highmem, and let's go back to
> Laura's patch:
>
> old:
> #define virt_addr_valid(kaddr) (((void *)(kaddr) >= (void *)PAGE_OFFSET) && \
> ((void *)(kaddr) < (void *)high_memory))
> new:
> #define virt_addr_valid(kaddr) pfn_valid(__pa(kaddr) >> PAGE_SHIFT)
>
> The former _excludes_ highmem, but the latter _includes_ it.
>
> virt_addr_valid(v) should only ever return _true_ for the lowmem area,
> never anywhere else - that's part of its point. It's there to answer
> the question "is this a valid virtual pointer which I can dereference".
>
> So... We actually need a combination of both of these tests.
Just to avoid any confusion, on arm64 we don't have non-linear v:p
translation as there is plenty of VA space to live with holes. So the
original patch is fine.
On 32-bit, it could be a problem if you have holes in the VA space, so
it needs both high_memory and pfn_valid checks.
--
Catalin
next prev parent reply other threads:[~2013-12-12 17:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-11 1:23 [PATCH] arm: Correct virt_addr_valid Laura Abbott
2013-12-11 1:23 ` [PATCH] arm64: " Laura Abbott
2013-12-11 10:44 ` Will Deacon
2013-12-11 11:06 ` Russell King - ARM Linux
2013-12-11 17:26 ` Will Deacon
2013-12-11 21:13 ` Russell King - ARM Linux
2013-12-12 17:57 ` Catalin Marinas [this message]
2013-12-12 18:02 ` Russell King - ARM Linux
2013-12-12 22:09 ` Laura Abbott
2013-12-13 11:57 ` Catalin Marinas
2013-12-16 18:28 ` Laura Abbott
2013-12-17 14:19 ` Catalin Marinas
2013-12-11 17:35 ` Laura Abbott
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