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SubjectRe: EFAULT reading /dev/mem... - broken x86info


Manfred Spraul wrote:

> Petr Vandrovec wrote:
>
>> On Mon, Nov 10, 2003 at 06:17:37PM +0100, Manfred Spraul wrote:
>>
>>
>>> DEBUG_PAGEALLOC unmaps pages on kmem_cache_free and __free_pages().
>>> The pages are mapped again during get_free_pages and kmem_cache_alloc.
>>>
>>> 0x86000 looks like a normal page - what guarantees that it's not
>>> used by the kernel?
>>>
>>
>>
>> With DEBUG_PAGEALLOC there is no problem with page if it is USED by
>> the kernel.
>> Problem is if page is NOT USED - in this case kernel does not have it
>> in its
>> mapping, and bad thing happen.
>>
>>
> If the page is used by AGP, then it won't have a mapping either.
>
afaics, agp uses change_apge_attr() to turn on NOCACHE bit, and doesn't
remove the mapping.

--Mika




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