Re: kvm PCI assignment & VFIO ramblings

Alexander Graf
2011-08-25T13:25:45Z

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On 25.08.2011, at 07:31, Roedel, Joerg wrote:

> On Wed, Aug 24, 2011 at 11:07:46AM -0400, Alex Williamson wrote:
>> On Wed, 2011-08-24 at 10:52 +0200, Roedel, Joerg wrote:
>

[...]

>> We need to try the polite method of attempting to hot unplug the device
>> from qemu first, which the current vfio code already implements. We can
>> then escalate if it doesn't respond. The current code calls abort in
>> qemu if the guest doesn't respond, but I agree we should also be
>> enforcing this at the kernel interface. I think the problem with the
>> hard-unplug is that we don't have a good revoke mechanism for the mmio
>> mmaps.
>
> For mmio we could stop the guest and replace the mmio region with a
> region that is filled with 0xff, no?

Sure, but that happens in user space. The question is how does kernel space enforce an MMIO region to not be mapped after the hotplug event occured? Keep in mind that user space is pretty much untrusted here - it doesn't have to be QEMU. It could just as well be a generic user space driver. And that can just ignore hotplug events.

Alex

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