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

[Jean Guyader <jean.guyader@xxxxxxxxx>]

On 26 December 2011 10:06, Kai Huang <mail.kai.huang@xxxxxxxxx> wrote:
> On Mon, Dec 26, 2011 at 4:54 PM, Jean Guyader <jean.guyader@xxxxxxxxx> wrote:
>> 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
>
> Oh. Is there any plan, or code branch we are working on to support
> PCIE bus in xen/qemu now?
>

Someone can correct me if I'm wrong but I don't think qemu upstream
has pcie support yet.
When qemu upstream will have pcie support we will get it for free.

Jean

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