Re: [Xen-devel] Issues with PCI-Passtrough (VT-d) in HVM with Xen 4.6

[Andrey Grodzovsky <andrey2805@xxxxxxxxx>]

On Wed, Jun 15, 2016 at 9:14 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:

>>> On 15.06.16 at 12:45, <andrey2805@xxxxxxxxx> wrote:
> In reply to -
> http://lists.xen.org/archives/html/xen-devel/2016-06/msg00622.html
>
> HI, I am working with Jurgen on the issue, as per Jan's request I tried to
> write explicitly only latency timer to be written -
> bool force_write = false;
> if ((dev_data->permissive || xen_pcibk_permissive) &&
>               offset == PCI_CACHE_LINE_SIZE && size == 4)
>              force_write = true;
> ...
>
> if ((force_write || !handled) && !err) {...}
>
> But then it exposed another issue, the command register field seems not to
> be restored also
> because I think the bits which are to be restored are not
> in PCI_COMMAND_GUEST mask.

Please be more precise: Which bits in particular are not getting
set back to the needed values (I would guess the memory
and/or I/O decode ones, which we specifically must not allow
the guest to control, but I'd like to be certain)?

 

Indeed, 0x103 which would be  MEMORY,IO and SERR.

If my guess is correct, then I think rather than adding some
hackish workaround to pciback you'd better see whether there's
a way to cause a pci_disable_device() through your driver before
the reset, and a pci_enable_device() after. Or actually, I think
you can do this via plain config space writes from your driver: Try
writing the Command Register with the two decode bits clear
right before restoring the intended value (see the logic close to
the top of command_write()).

Jan

So i tried the first option, as you suggested by writing to /sys/bus/pci/devices/0000\:00\:00.0/enable

'0' == disable before reset and '1' == enable after from the test app, but no writes get through to pic-back on DOM0 , only the reads.

But this basically still tries to write the MEMORY and IO bits to command register down the call stack in pci_enable_resources 

which would again be blocked in xen-pciback xen_pcibk_config_write or am I missing something ?

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