Re: [libvirt] [PATCH v6 00/13] PCI passthrough support on s390
On Fri, 2018-10-12 at 16:04 +0100, Daniel P. Berrangé wrote:
On Fri, Sep 28, 2018 at 04:46:13PM +0800, Yi Min Zhao wrote:
[...]
> <hostdev mode='subsystem' type='pci'>
> <driver name='vfio'/>
> <source>
> <address domain='0x0001' bus='0x00' slot='0x00'
function='0x0'/>
> </source>
> <address type='pci' domain='0x0000' bus='0x00'
slot='0x01' function='0x0'>
> <zpci uid='0x0003' fid='0x00000027'/>
> </address>
> </hostdev>
I'm not sure if this was discussed in earlier versions, but to me
this use of a child element looks wrong.
What we're effectively saying is that s390 has a different addressing
scheme. It happens to share some fields with the current PCI addressing
scheme, but it is none the less a distinct scheme.
IOW, I think it should be
<address type='zpci' domain='0x0000' bus='0x00'
slot='0x01'
function='0x0' uid='0x0003'
fid='0x00000027'/>
Of course internally we can still share much logic for assigning the
addreses between "pci" and "zpci".
So what happens with PCI devices on s390 is that *two* devices will
be added to the guest: one is the usual virtio-net-pci or what have
you, which has its own PCI address allocated using the same algorithm
as other architectures; the other one is a '-device zpci', which IIUC
works basically like an adapter between the PCI device itself and the
guest OS, and which is identified using uid and fid.
Calling it a completely different address type seems like a bit of a
stretch: there is definitely a PCI address involved, which is why the
zPCI part was implemented through a potentially reusable "PCI address
extension" mechanism.
--
Andrea Bolognani / Red Hat / Virtualization