[openib-general] Reserved L_Key API

[Grant Grundler]

On Wed, Sep 15, 2004 at 08:42:53AM -0700, Roland Dreier wrote:
>     Fabian> Are the ramifications of such an RKEY any worse than those
>     Fabian> of locally attached DMA-capable adapters?

Not if one can guarantee it's well behaved.

>     Fabian> If your FC HBA
>     Fabian> goes haywire and decides to write all over memory, there's
>     Fabian> not much you can do.

That's not true. There are platforms that can isolate the FC and
prevent the FC HBA from scribbling to anything the respective driver
didn't previously get explicite write permission. ie we can guarantee
the containment.

However, for platforms that have 1:1 IO/CPU addressing (aka PCI
is identity mapped with CPU physical) and no error containment,
it would work as well as anything.

> All I can say is that in the real world people don't like it.  That's
> why features like remote invalidate get added.

In the real world, things occasionally do go haywire and that's why
sometimes it's useful to have error containment.
Deciding to add features that don't work with error containment
is ok - just make sure there is workable alternative.

Caveat: I'll have to re-read this thread in the morning. I'm pretty
sure I'm not registering some of the acronyms right now (e.g. PD).

thanks,
grant