Rep:Re: Rep:Re: Rep:Re: [f-cpu] TLB resume

["Nicolas Boulay" <nicolas.boulay@ifrance.com>]

-----Message d'origine-----
De: Yann Guidon <whygee@f-cpu.org>
A: f-cpu@seul.org
Date: 09/08/02
Objet: Re: Rep:Re: Rep:Re: [f-cpu] TLB resume

hi,

Michael Riepe wrote:
> On Fri, Aug 09, 2002 at 12:52:33AM +0200, nico wrote:
> [...]
> > > Consider this system call:
> > >
> > >         read(fd, &kernel_page, page_length);
> > >
> >
> > Why you're read can't check if the given pages are a real user one ?
> > It's easy under linux 0-2Gb is for process, 2-4 Gb AS is for kernel.
> 
> It's not always so easy. You'll have to check the memory mappings of
> the user process (in software) which may become quite expensive.

In Bordeaux, there was an idea of adding an instruction that would
return the access rights and mapping associated to a pointer.
this could help... and since F-CPU uses "split loads/stores"
it should not be too difficult.

>>> You make an access to the memory and if it's trap you does not have
this right ;p I don't like this too much because a task could see that
there are virtualise (it's like seing that an os is not running with
superuser mode). I think that such check must be done inside the table
of the OS. What does this instruction do if the data is not present in
the TLB ? A tlb miss ?
nicO

WHYGEE
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______________________________________________________________________________
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