[openib-general] Re: mthca FMR correctness (and memory windows)

[Fabian Tillier]

On 3/21/06, Michael S. Tsirkin <mst at mellanox.co.il> wrote:
> Quoting Fabian Tillier <ftillier at silverstorm.com>:
> > I'd still be interested in seeing regular registration calls improved,
> > as it's clear that an application that is sensitive about its security
> > must either restrict itself to send/recv, buffer the data (data copy
> > overhead), or register/unregister for each I/O.
>
> I guess regular registration calls could be improved, but the benefit is not all
> that obvious.
>
> Which applications do register/unregister for each I/O?

I think if register/unregister wasn't so painfully slow, a lot more
applications would do it.  It's the most secure, and unlike memory
windows, supports scatter gather.

There was enough people who wanted to register on the fly that
Mellanox invented their FMR implementation - regular registration
wasn't cutting it.  Otherwise, why would there be a need for it?

The problem with the mthca FMRs is that they're still insecure, on par
with the full frontal DMA MR from a security standpoint.  Anyone
worried about security is stuck with good old regular registration, or
memory windows.

- Fab