Re: [Qemu-devel] [PATCH] virtio-pci: enable bus master for old guests

[Nikunj A Dadhania]

Greg Kurz <address@hidden> writes:

>> > > I did some debugging: it looks like the guest kernel calls the OF
>> > > quisece call to flush pending DMA and disables bus master on the
>> > > virtio-blk device (PCI_COMMAND == 0x3).
>> > 
>> > Getting confused, above you are talking about virtio-net and here it is
>> > virtio-blk.
>> > 
>> > Anyways, the routines still remains same for both of them.  From SLOF
>> > during init we set DRIVER_OK, and after using the device during the
>> > quiesce, called from linux kernel VIRTIO_CONFIG_S_FAILED is set and then
>> > a VIRTIO_DEVICE_RESET is done.
>> 
>> BTW, you really should start enabling bus mastering, avoid relying
>> on the work-around we have for broken guests.
>> 
>
> FWIW during my debug session, I see that SLOF enables bus mastering...
> unfortunately, it gets disabled at some point after the guest kernel
> is started (around the ppc64 prom_init() call).

Is it before quiesce call?

Regards
Nikunj