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Re: [Xen-devel] RFC -- virtualisable NIC support in Xen

To: Caitlin Bestler <caitlinb@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] RFC -- virtualisable NIC support in Xen
From: Greg Law <glaw@xxxxxxxxxxxxxx>
Date: Wed, 27 Sep 2006 13:53:28 +0100
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Caitlin Bestler wrote:

-----Original Message-----
From: Greg Law [mailto:glaw@xxxxxxxxxxxxxx] Sent: Friday, September 22, 2006 4:05 AM
To: Caitlin Bestler
Cc: xen@xxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] RFC -- virtualisable NIC support in Xen

Caitlin Bestler wrote:

When the App/DomU posts a buffer (for TX or RX), what

address does it
use, and how does the hardware understand it?

It uses a "buffer address". This is essentially an index into a "buffer-table" which is stored on the NIC. This table is used to lookup physical addresses that the NIC will DMA to/from.

The buffer-table is programmed from Dom0.

The buffer-table is effectively our IOMMU/page-tables.

Over what scope is the buffer handle unique?

The buffer table is per NIC. The handle into that buffer table is tied to a particular Virtual Interface, meaning a guest driver can only DMA to/from buffers associated with the virtual interface to which it has access (the VIs are all mapped page aligned so that the usual paging can be used to prevent one guest from accessing the VI of another).

Can I ask what your interest is here? Do you think Broadcom might be interested in the kind of model we're proposing?



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