[virtio-comment] Re: [PATCH V2 6/6] virtio-pci: implement dirty page tracking

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 08, 2023 at 05:30:02PM +0800, Zhu, Lingshan wrote:
> 
> 
> On 11/7/2023 7:33 PM, Michael S. Tsirkin wrote:
> > On Tue, Nov 07, 2023 at 05:52:41PM +0800, Zhu, Lingshan wrote:
> > > > > > > > 2. the PCI FLR is clearing all the registers you exposed here.
> > > > > > > see above
> > > > > > > > 3. Endless expansion of config registers of dirty tracking is not
> > > > > > > > scalable, as they
> > > > > > > are not init time registers not following the Appendix B guidelines.
> > > > > > > endless expansion?? It is a complete set of dirty page tracking, right????
> > > > > > > have you see this cap only controls? The device DMA writes the
> > > > > > > bitmap, not by registers.
> > > > > > Device dirty page tracking is start/stop command to be done by the
> > > > > hypervisor.
> > > > > > So when guest is resetting the device, it stopped the DMA initiated by the
> > > > > hypervisor.
> > > > > > This fundamentally breaks things.
> > > > > Why? When device resets, do you want to keep tracking dirty pages????
> > > > Yes, when the device resets, before that event occurred, all the pages which were dirtied, must be migrated.
> > > > And after reset also new page tracking to continue.
> > > That depends on whether there is an interrupt for the dirty pages.
> > > If there is an interrupt, then the guest owns the pages
> > Not in the virtio model, guest owns the memory once buffer has been used.
> Yes and even better, interrupt happens after buffers marked as used.

But guest owns memory earlier and you can not change it after this
point.


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