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SubjectRe: Linux Graphics Architecture
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> >> There are several other serious problems, including the implicit
> >> assumption that graphics hardware will enforce security.
> >
> > You don't need hardware contexts.
>
> Read that again. Here:
> "must be context-switchable"
> "must be able to be performed preemptively"
> "in the middle of a command"
>
> Without that, you can crash the card when two apps send interleaved
> commands to the server. Do you intend to disable context switching
> and prohibit SMP hardware?

Of course not. The requirement is at the software interface level, not the
silicon on the card level.

So you can do several things. Eg you can use the mmu to block access
by another context pending I/O completion.

> Consider the common Matrox Millennium:
>
> 1. write 0x00000000 (commonly a black pixel) to video memory
> 2. tell the card to DMA that into the kernel
> 3. have fun as root

Ok then the matrox is a case where it can't do direct 2D render. It needs
helper code in the Xserver. It isnt the only one - try writing random bit
patterns to a Voodoo card (this btw is why the glide device driver isnt
worth a lot..)

Alan


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