Re: [Xen-devel] PCI Device Subtree Change from Traditional to Upstream

[Kevin Stange <kevin@xxxxxxxxxxxxx>]

On 01/03/2018 11:57 AM, Anthony PERARD wrote:
> On Wed, Dec 20, 2017 at 11:40:03AM -0600, Kevin Stange wrote:
>> Hi,
>>
>> I've been working on transitioning a number of Windows guests under HVM
>> from using QEMU traditional to QEMU upstream as is recommended in the
>> documentation.  When I move these guests, the PCI subtree for Xen
>> devices changes and Windows creates a totally new copy of each device.
>> Windows tracks down the storage without issue, but it treats the new
>> instance of the NIC driver as a new device and clears the network
>> configuration even though the MAC address is unchanged.  Manually
>> booting the guest back on the traditional device model reactivates the
>> original PCI subtree and the old network configuration with it.
>>
>> The only thing that I have been able to find that's substantially
>> different comparing the device trees is that the device instance ID
>> values differ on the parent Xen PCI device:
>>
>> PCI\VEN_5853&DEV_0001&SUBSYS_00015853&REV_01\3&267A616A&3&18
>>
>> PCI\VEN_5853&DEV_0001&SUBSYS_00015853&REV_01\3&267A616A&3&10
>>
>> Besides actually setting the guest to boot using QEMU traditional, is
>> there a way to convince Windows to treat these devices as the same?  A
>> patch-based solution would be acceptable to me if there is one, but I
>> don't understand the code well enough to create my own solution.
> 
> Hi Kevin,
> 
> I've got a patch to QEMU that seems to do the trick:
> 
> From: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> Subject: [PATCH] xen-platform: Hardcode PCI slot to 3
> 
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
>  hw/i386/pc_piix.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index 5e47528993..93e3a9a916 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -405,7 +405,7 @@ static void pc_xen_hvm_init(MachineState *machine)
>  
>      bus = pci_find_primary_bus();
>      if (bus != NULL) {
> -        pci_create_simple(bus, -1, "xen-platform");
> +        pci_create_simple(bus, PCI_DEVFN(3, 0), "xen-platform");
>      }
>  }
>  #endif
> 
> 
> The same thing could be done by libxl, by providing specific command
> line options to qemu. (I think that could even be done via a different
> config file for the guest.)

This patch doesn't seem to work for me.  It seems like the device model
process is exiting immediately, but I haven't been able to find any
information as to what is going wrong.  I tested with Xen 4.6.6 and the
QEMU packaged with that release.  Should I try it on a different version
of Xen and QEMU?

-- 
Kevin Stange
Chief Technology Officer
Steadfast | Managed Infrastructure, Datacenter and Cloud Services
800 S Wells, Suite 190 | Chicago, IL 60607
312.602.2689 X203 | Fax: 312.602.2688
kevin@xxxxxxxxxxxxx | www.steadfast.net

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