Re: [Xen-devel] PCI Passthrough bug with x86 HVM

[Chao Gao <chao.gao@xxxxxxxxx>]

On Wed, Jun 26, 2019 at 03:36:35PM +0200, Juergen Gross wrote:
>On 26.06.19 14:21, Chao Gao wrote:
>>On Wed, Jun 26, 2019 at 08:17:50AM +0200, Juergen Gross wrote:
>>>On 24.06.19 20:47, Stefano Stabellini wrote:
>>>>+ xen-devel
>>>>
>>>>On Mon, 24 Jun 2019, Stefano Stabellini wrote:
>>>>>Hi all,
>>>>>
>>>>>I might have found a bug with PCI passthrough to a Linux HVM guest on
>>>>>x86 with Xen 4.12. It is not easy for me to get access, and especially
>>>>>change components, on this particular system, and I don't have access to
>>>>>other x86 boxes at the moment, so apologies for the partial information
>>>>>report. The setup is as follow:
>>>>>
>>>>>- two PCI devices have been assigned to a HVM guest, everything is fine
>>>>>- reboot the guest from inside, i.e. `reboot' in Linux
>>>>>- after the reboot completes, only one device is assigned
>>>>>
>>>>>Before the reboot, I see all the appropriate xenstore entries for both
>>>>>devices. Everything is fine. After the reboot, I can only see the
>>>>>xenstore entries of one device. It is as if the other device
>>>>>"disappeared" without throwing any errors.
>>>>>
>>>>>Have you seen this before? Do you know if it has been fixed in staging?
>>>>>I noticed this fix which seems to be very relevant:
>>>>>
>>>>>https://lists.xenproject.org/archives/html/xen-devel/2018-11/msg01616.html
>>>>>
>>>>>but it is already included in 4.12.
>>>
>>>Stefano, could you please try the attached patch? It is only compile
>>>tested for now.
>>>
>>>
>>>Juergen
>>
>>>From ea95dcdfc60a895cc43baf34c8e0fb088e10008d Mon Sep 17 00:00:00 2001
>>>From: Juergen Gross <jgross@xxxxxxxx>
>>>To: xen-devel@xxxxxxxxxxxxxxxxxxxx
>>>Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
>>>Cc: Wei Liu <wl@xxxxxxx>
>>>Date: Wed, 26 Jun 2019 08:15:28 +0200
>>>Subject: [PATCH] libxl: fix pci device re-assigning after domain reboot
>>>
>>>After a reboot of a guest only the first pci device configuration will
>>>be retrieved from Xenstore resulting in loss of any further assigned
>>>passed through pci devices.
>>>
>>>The main reason is that all passed through pci devices reside under a
>>>common root device "0" in Xenstore. So when the device list is rebuilt
>>>from Xenstore after a reboot the sub-devices below that root device
>>>need to be selected instead of using the root device number as a
>>>selector.
>>>
>>>Fix that by adding a new member to struct libxl_device_type which when
>>>set is used to get the number of devices. Add such a member for pci to
>>>get the correct number of pci devices instead of implying it from the
>>>number of pci root devices (which will always be 1).
>>>
>>>While at it fix the type of libxl__device_pci_from_xs_be() to match
>>>the one of the .from_xenstore member of struct libxl_device_type. This
>>>fixes a latent bug checking the return value of a function returning
>>>void.
>>>
>>>Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>
>>Tested-by: Chao Gao <chao.gao@xxxxxxxxx>
>
>Thanks!
>
>>
>>Note that I just tested it on RELEASE-4.12.0, not staging.
>>
>>I also found USB device would miss across reboot. Is there someone
>>willing to fix it too?
>
>I'll have a look.
>

In guest configuration file, it has following two lines:

usbctrl=['type=devicemodel,version=1']
usbdev=['type=hostdev,hostbus=1,hostaddr=3,controller=0,port=1']

Attachments are output of 'xenstore-ls' before and after reboot 

Thanks
Chao

Attachment: xenstore-before
Description: Text document

Attachment: xenstore-after
Description: Text document

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