linux-kernel - Re: mtd: kernel BUG at arch/x86/mm/pat.c:279!

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Date:	Mon, 10 Sep 2012 07:17:04 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>, dwmw2@...radead.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mtd@...ts.infradead.org, linux-mm <linux-mm@...ck.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: mtd: kernel BUG at arch/x86/mm/pat.c:279!

On 09/09/2012 06:56 PM, H. Peter Anvin wrote:
>>
>> Anyway, that means that the BUG_ON() is likely bogus, but so is the
>> whole calling convention.
>>
>> The 4kB range starting at 0xfffffffffffff000 sounds like a *valid*
>> range, but that requires that we fix the calling convention to not
>> have that "end" (exclusive) thing. It should either be "end"
>> (inclusive), or just "len".
>>
> 
> On x86, it is definitely NOT a valid range.  There is no physical addresses
> there, and there will never be any.

This reminds me a similar issue: If you try to mmap /dev/kmem at an offset which
is not kernel owned (such as 0), you'll get all the way to __pa() before getting
a BUG() about addresses not making sense.

How come there's no arch-specific validation of attempts to access
virtual/physical addresses? In the kmem example I'd assume that something very
early on should be yelling at me about doing something like that, but for some
reason I get all the way to __pa() before getting a BUG() (!).


Thanks,
Sasha
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