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Re: [Xen-devel] [question] Does HVM domain support xen-pcifront/xen-pciback?

On Mon, Feb 06, 2012 at 04:32:05PM +0800, Kai Huang wrote:
> Hi,
> I see in pcifront_init, if domain is not PV domain, pcifront_init just
> returns error. So seems HVM domain does not support
> xen-pcifront/xen-pciback mechanism? If it is true, why? I think

Yup. B/c the only thing that the PV PCI protocol does is enable
PCI configuration emulation. And if you boot an HVM guest - QEMU does
that already.

> technically there's nothing that can block to support pcifront/pciback
> in HVM, and for performance reason, there will be benefits if HVM
> supports PV PCI operation.

Nope. The PCI operations are just for writting configuration deta in the
PCI space. Whcih is done mostly when a driver starts/stops and no more.

The performance is with interrupts and how to inject them in a guest - and
in there the PV is much faster than HVM due to the emulation layer complexity.
However, work by Stefano on making that path shorter has made the interrupt
injection much much faster.

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