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

[Jean Guyader <jean.guyader@xxxxxxxxx>]

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

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