Re: [Xen-devel] How does domU access PCI configure space?

[Jean Guyader <jean.guyader@xxxxxxxxx>]

On 26 December 2011 09:50, Kai Huang <mail.kai.huang@xxxxxxxxx> wrote:
> On Mon, Dec 26, 2011 at 4:22 PM, Jean Guyader <jean.guyader@xxxxxxxxx> wrote:
>> On 26 December 2011 07:02, Kai Huang <mail.kai.huang@xxxxxxxxx> wrote:
>>> Hi,
>>>
>>> In my understanding, domU's PCI configure space access (ncluding
>>> virtual device's and direct io's) is always trapped and emulated by
>>> xen hypervisor. How did xen do it? Through exposing PCI configure
>>> space area to domU as non-accessible memory? Where's the code to deal
>>> of this? Thanks!
>>>
>>
>> Config space access happen through the IO port cf8 and cfc.
>> When a guest write to an io port that will cause a VMEXIT then xen will
>> forward the io port request to qemu. cf8 and cfc are owned by the PCI
>> BUS device model in qemu then this code will interpret the config
>> space request and send it to the right pci device model (code
>> qemu/i386-dm/helper2.c qemu/hw/pci.c)
>>
>> Jean
>
> IO port only works for PCI device, and in real system should only be
> used during early boot phase. All PCIE devices must use MMIO mechanism
> to access configure space.
>
> Are you saying currently xen/qemu only exports PIO mechanism to domU,
> and does not support PCIE devices emulation/passthrough?
>

xen/qemu doesn't emulate a PCIE bus, it only has PCI support.

Jean

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