Next steps for pci-rework branches

Alan Cox alan at
Mon Aug 14 05:51:34 PDT 2006

Ar Sul, 2006-08-13 am 15:42 +0200, ysgrifennodd Erwin Rol:
> > 1. Mappings can take up valueable resource in the kernel.
> Doesn't mapping several small regions instead of one big region take up
> more resources ?

It takes a lot more resources to map large areas of unused space than to
split them.

> > 2. Mapping the whole BAR might expose "dangerous" registers that could
> >    be accidentally (or on purpose by a malicious attacker) accessed.
> >    It's much better to not map these registers in the first place.
> If the library can map them, anything else can map them too. So if your
> x-server/driver gets hacked it doesn't help you at all when only "safe"
> registers are mapped. 

That depends on what privileges are dropped and when they are dropped.
At the very least it can be preferable to protect against accidental
misuse, and the vga map/unmap code has caught people before for example.

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