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Re: [Qemu-devel] [RFC PATCH] qemu pci: pci_add_capability enhancement to


From: Alex Williamson
Subject: Re: [Qemu-devel] [RFC PATCH] qemu pci: pci_add_capability enhancement to prevent damaging config space
Date: Fri, 08 Jun 2012 09:22:00 -0600

On Fri, 2012-06-08 at 17:05 +0200, Jan Kiszka wrote:
> On 2012-06-08 16:56, Alex Williamson wrote:
> > The difference between VFIO and kvm device assignment is that VFIO
> > emulates a lot of config space for us, so most things are passed
> > through.
> 
> That's not different from current device assignment, is it? I think the
> major difference is that VFIO filters and potentially post-processes the
> direct writes in kernel space.

Right, and having the filtering/virtualization in the kernel means that
qemu only handles a very small subset of PCI config space.  That's made
us lax in even telling qemu about the areas that it'll never see
accesses too.  For current device assignment, since we doing the
emulation in qemu, it's a little more beneficial to register everything.
Thanks,

Alex




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