Re: [Xen-devel] [Hackathon minutes] PV network improvements

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, May 20, 2013 at 03:08:05PM +0100, Stefano Stabellini wrote:
> Hi all,
> these are Konrad's and my notes (mostly Konrad's) on possible
> improvements of the PV network protocol, taken at the Hackathon.
> 

Just for completeness, these items are future working items. I'm now
upstreaming my queues to lay a baseline for these items, which include:

1. split event channels support (generally useful)
2. netback global page pool (prerequisite for 1:1 model)
3. kthread + NAPI 1:1 model (prerequisite for multiqueue)

> 
> A) Network bandwidth: multipage rings
> The max outstanding amount of data the it can have is 898kB (64K of
> data use 18 slot, out of 256. 256 / 18 = 14, 14 * 64KB).  This can be
> expanded by having multi-page to expand the ring. This would benefit NFS
> and bulk data transfer (such as netperf data).
> 

This is in my queue as well. It's generic change in xenbus interface
which can benefit not only network but also block device.

> 
[...]
> J) Map the whole physical memory of the machine in dom0
> If mapping/unmapping or copying slows us down, could we just keep the
> whole physical memory of the machine mapped in dom0 (with corresponding
> IOMMU entries)?
> At that point the frontend could just pass mfn numbers to the backend,
> and the backend would already have them mapped.
> >From a security perspective it doesn't change anything when running
> the backend in dom0, because dom0 is already capable of mapping random
> pages of any guests. QEMU instances do that all the time.
> But it would take away one of the benefits of deploying driver domains:
> we wouldn't be able to run the backends at a lower privilege level.
> However it might still be worth considering as an option? The backend is
> still trusted and protected from the frontend, but the frontend wouldn't
> be protected from the backend.
> 

I think Dom0 mapping all machine memory is a good starting point. As for
the driver domain, can we not have a driver domain mapped all of its
target's machine memory? What's the security implication here?


Wei.

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