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Re: [libvirt] [PATCH 0/6] RFC: qemu: virtio-{non-}transitional support



On 01/15/2019 08:30 AM, Andrea Bolognani wrote:
On Sun, 2019-01-13 at 18:12 -0500, Cole Robinson wrote:
[...]
The main RFC bits here are:
...

* The PCI address handling. I just mapped virtio-non-transitional
   to imply plain PCI addressing. I think that's all we need but
   I'm not positive so I'd appreciate a review of that approach.

I don't think that's right. Let me fish up a message I wrote a while
ago summing up interactions between VirtIO devices and PCI (Express)
slots:

   http://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg03133.html

Basically VirtIO 0.9 requires IO space to be available, and 1.0 did
away with that requirement because PCI Express, unlike conventional
PCI, allows devices *not* to have IO space.

So transitional devices, which must work with both 0.9 and 1.0, can
depend on IO space being available and as such will only work when
plugged into conventional PCI slots, whereas non-transitional
devices don't need IO space and can thus be plugged into either
conventional PCI and PCI Express slots.

Ultimately, then, transitional (rather than non-transitional)
devices are the ones that must be forced into conventional PCI
slots.


Okay thanks for the correction, so that sounds like for NON_TRANSITIONAL we should also be forcing pcieFlags. I've made those changes and updated the branch here: https://github.com/crobinso/libvirt/tree/virtio

Thanks,
Cole


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