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

[Mika Penttilä]

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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