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Re: [Xen-devel] [Query] Flow of PCI device dedicated to a domU
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On 16/07/14 07:12, Xenbegn developer
wrote:
Hi,
I am trying to understand the flow of how a PCI
device driver in domU works after a PCI device is is
assigned to a domU.
a) If a PCI device is assigned to a domU, this device
has to be on a PCI bus. So as per my view xen would
have to somehow provide a PCI Controller on which this
device is attached.
=> Is my assumption correct ? If yes how it is done,
No then also How enumeration of this device happens in
domU kernel
No.
PV guests have no PCI root ports/bridges; they use devices as single
entities knowing that Xen/dom0 takes care of the other bits. HVM
guests have their PCI devices attached to the virtual southbridge
which is all emulated by Qemu.
b) Is the Configuration space of the PCI device directly
accessible to the domU (assuming the kernel accesses it
using memory map) ? If not then it is trapped by xen
All configuration space is trap+emulate in Xen, although almost all
operations permitted.
c) Who assigns the MSI (addr + value) in the PCI device. If
Xen then how Xen does a translation from Physical MSI to
guest MSI (where in code)
Xen controls all interrupts on the system, which is why it needs to
trap all config accesses to notice when a domain is attempting to
change the interrupt information. In that case, Xen fixes up its
delivery of interrupts to the guest, but leaves the underlying
interrupt information intact.
~Andrew
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