Re: [Qemu-discuss] Add PCI Passthrough for multiple devices on same bus?

[Tony Su]

OK,
Some fundamentals...

There are many benefits whenever you virtualize, and ideally you
should try to virtualize as much of the whole solution as possible. I
won't try to itemize all benefits but just the fact you're running
QEMU must mean you understand at least some of the benefits.

There are three main areas of virtualization starting with CPU/RAM and
early virtualization assumed virtualizing these in some way would
always exist and was always part of even first generation
virtualization. Later, I/O virtualization was and is still being
introduced. And lastly, storage has always been recommended to be
implemented virtualized, usually as a backing file (mounted possibly
as a loop device). Virtualized storage has been around almost since
the beginning and has been recommended so as to ensure isolation,
avoid contention and remove the issues involved accessing the Host
file system directly.

So, to be more clear and describing in relation to your situation,
these issues you have about exposing PCI pass-through  to the VM
should be unnecessary. As long as connectivity exists for the Host,
then the virtualization technology running on the Host (QEMU in your
case) should be able to manage virtual storage, and provide a
configured storage (typically a backing file aka virtual disk file) to
the Guest VM. The Guest VM never has to access the hardware directly,
it only sees the virtualized fs provided by the Host which <does> know
how to access the storage using whatever driver is necessary.

I wouldn't know how to analyze much less troubleshoot your PCI
pass-through without closer inspection but as I described shouldn't be
necessary unless you have a special need.

HTH,
TSU

On Tue, Sep 10, 2013 at 12:05 PM, Andrew Martin <address@hidden> wrote:
> Tony,
>
> I am using virt-manager, but also receive this same error when attempting
> to add a second serial port through the GUI. I believe the issue is that
> all 4 of the serial ports on this card appear on the same bus. Is there a
> way to add more than one device that is on the same bus to the VM?
>
> I am not familiar with the "virtual storage" method that you mention. Can
> this be used with non-storage devices, such as a serial card? Do you have
> any documentation on this feature?
>
> Thanks,
>
> Andrew
>
> ----- Original Message -----
>> From: "Tony Su" <address@hidden>
>> To: "Andrew Martin" <address@hidden>
>> Cc: "qemu_mail" <address@hidden>
>> Sent: Sunday, September 8, 2013 6:42:14 PM
>> Subject: Re: [Qemu-discuss] Add PCI Passthrough for multiple devices on same 
>> bus?
>>
>> Since you're using virsh commands, have you also considered just
>> running vm manager if you're running a graphical environment? It's
>> pretty straightforward when you use vm manager if there isn't a
>> conflict of some sort...
>>
>> Also, just wondering if you really need to access the hardware
>> directly, it's more typical to let the Host access the hardware
>> directly and create virtual storage on the hardware for VM use
>> instead. If you don't have a specific need, there are many benefits
>> doing it the more usual virtualized storage way.
>>
>> Tony
>>
>> On Thu, Sep 5, 2013 at 3:15 PM, Andrew Martin <address@hidden>
>> wrote:
>> > Hello,
>> >
>> > I have a 4-port PCIe serial card that I would like to pass through
>> > to a VM. The serial card has 4 serial ports on it, and I would
>> > like to pass all 4 ports through. Here are the ports, as seen on
>> > the host:
>> > # lspci
>> > 02:00.0 Serial controller: MosChip Semiconductor Technology Ltd.
>> > 4-Port PCIe Serial Adapter
>> > 02:00.1 Serial controller: MosChip Semiconductor Technology Ltd.
>> > 4-Port PCIe Serial Adapter
>> > 02:00.2 Serial controller: MosChip Semiconductor Technology Ltd.
>> > 4-Port PCIe Serial Adapter
>> > 02:00.3 Serial controller: MosChip Semiconductor Technology Ltd.
>> > 4-Port PCIe Serial Adapter
>> >
>> > # virsh nodedev-list
>> > pci_0000_02_00_0
>> > pci_0000_02_00_1
>> > pci_0000_02_00_2
>> > pci_0000_02_00_3
>> >
>> > I have configured the first port, 02:00.0 , in my VM configuration
>> > file as follows:
>> > <hostdev mode='subsystem' type='pci' managed='yes'>
>> >       <source>
>> >         <address domain='0x0000' bus='0x02' slot='0x00'
>> >         function='0x0'/>
>> >       </source>
>> >       <address type='pci' domain='0x0000' bus='0x00' slot='0x05'
>> >       function='0x0'/>
>> > </hostdev>
>> >
>> > If I attempt to start the VM, I get the following error:
>> > error: internal error Unable to reset PCI device 0000:02:00.1:
>> > internal error Active 0000:02:00.0 devices on bus with
>> > 0000:02:00.1, not doing bus reset
>> >
>> > Running the following commands to detach the other 3 ports then
>> > allows me to successfully start the VM, and I can see the serial
>> > port in it:
>> > # virsh nodedev-detach pci_0000_02_00_1
>> > # virsh nodedev-detach pci_0000_02_00_2
>> > # virsh nodedev-detach pci_0000_02_00_3
>> >
>> > However, when I attempt to add more than 1 of the ports to the VM
>> > config, I keep getting this error:
>> > error: internal error Unable to reset PCI device 0000:02:00.1:
>> > internal error Active 0000:02:00.0 devices on bus with
>> > 0000:02:00.1, not doing bus reset
>> >
>> > The second port I added (0000:02:00.1) is configured as follows in
>> > the VM config:
>> >     <hostdev mode='subsystem' type='pci' managed='yes'>
>> >       <source>
>> >         <address domain='0x0000' bus='0x02' slot='0x00'
>> >         function='0x1'/>
>> >       </source>
>> >       <address type='pci' domain='0x0000' bus='0x00' slot='0x06'
>> >       function='0x0'/>
>> >     </hostdev>
>> >
>> > How can I add all 4 of these devices (which share the same bus) as
>> > PCI passthrough to the VM?
>> >
>> > Thanks,
>> >
>> > Andrew
>> >
>>