linux-kernel - Re: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG

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Message-ID: <48E3D6FC.7070709@gmail.com>
Date:	Wed, 01 Oct 2008 22:01:00 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Vegard Nossum <vegard.nossum@...il.com>,
	Vegard Nossum <vegardno@....uio.no>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y

On 10/01/2008 09:46 PM, Andi Kleen wrote:
>> Anyway virt_addr_valid() is IMHO wrong. E.g. first modules VM address
>> 0xffffffffa0000000 is after __pa() 200M which is valid pfn after the shift even
>> on the flatmem model with enough memory.
>>
>> Am I missing something? What's the exact purpose of the virt_addr_valid()?
> 
> I think it's supposed to be only used on direct mapping anyways (judging
> from a quick look a the users)

Then kmemcheck assumes something else. Citing:
 * We need to be extremely careful not to follow any invalid pointers,
 * because this function can be called for *any* possible address.
and the very first check is !virt_addr_valid(address).

> So not handling text mapping is ok, but don't panic on it.

It doesn't handle properly anything but text and direct mapping. Now it
oopses/causes BUG on that wrong cases.

I think we should set it down there that it was intended to be used only on
text/direct mapping and only for checking if there is a physical memory page
behind this kind of virtual address.
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