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

[Chao Gao <chao.gao@xxxxxxxxx>]

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>

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?

Thanks
Chao

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