On Wed, Mar 19, 2008 at 02:25:36PM -0400, Leichter, Jerry wrote:

[This has been thrashed out on other lists.]

> Just how would that help?  As I understand it, Firewire and PCMCIA
> provide a way for a device to access memory directly.  The OS doesn't
> have to do anything - in fact, it *can't* do anything.

The OS can program the Firewire controller not to allow DMA.

> The only possible protection here is at the hardware level:  The
> external interface controller must be able to run in a mode which
> blocks externally-initiated memory transactions.  Unfortunately,
> that may not be possible for some controllers.  Sure, the rules for
> (say) SCSI might say that a target is only supposed to begin sending
> after a request from an initiator - but it would take a rather
> sophisticated state machine to make sure to match things up properly,
> especially on a multi-point bus.

Isn't what you're describing here an IOMMU?


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