Re: [Xen-devel] How does vmm get all mmio areas of pci devices?

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Thu, Dec 1, 2011 at 2:08 AM, confucius <henanwxr@xxxxxxxxxxx> wrote:
> what I want to know is step2 and step5:
> In step2, how does vmm get all mmio areas of devices? and how vmm set ept
> entry with these mmio areas ?

At the moment, Xen will send all accesses to guest physical addresses
it doesn't recognize to qemu.  There is a general plan to have qemu
register these areas with Xen before starting the guest, but that's
not being actively worked on at the moment, AFAIK.

> In setp5, is it ture for DMA operatin I described? and when qemu-dm find no
> callback function for some MMIO area, what it will do?

I don't understand your thing about DMA.  DMA is emulated by QEMU; but
it's not done to MMIO regions, but to memory regions.  A guest driver
shouldn't request a DMA to a region of the physical address space that
isn't backed by RAM; if it tries to, the request will fail in QEMU.
(Not sure exactly what will happen.)

In any case, if qemu gets an MMIO request from the guest on an area of
physical memory where it doesn't have any devices, it will just pass
the request back to Xen without doing anything.  I believe this
typically this will results in writes doing nothing and reads getting
0.

 -George

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