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

[Kai Huang <mail.kai.huang@xxxxxxxxx>]

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?

Thanks.

-cody

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