"Michael S. Tsirkin" <m...@redhat.com> writes:
> On Wed, Sep 10, 2014 at 01:44:49PM +0530, Nikunj A Dadhania wrote:
>> Greg Kurz <gk...@linux.vnet.ibm.com> writes:
>>
>> > On Mon, 8 Sep 2014 19:05:02 +0300
>> > "Michael S. Tsirkin" <m...@redhat.com> wrote:
>> >
>> >> commit cc943c36faa192cd4b32af8fe5edb31894017d35
>> >> pci: Use bus master address space for delivering MSI/MSI-X messages
>> >> breaks virtio-net for rhel6.[56] x86 guests because they don't
>> >> enable bus mastering for virtio PCI devices
>> >>
>> >> Old guests forgot to enable bus mastering, enable it
>> >> automatically on DRIVER_OK.
>> >>
>> >> Note: we should either back out the original patch from
>> >> stable or apply this one on top.
>> >>
>> >> Cc: qemu-sta...@nongnu.org
>> >> Reported-by: Greg Kurz <gk...@linux.vnet.ibm.com>
>> >> Signed-off-by: Jan Kiszka <jan.kis...@siemens.com>
>> >> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
>> >> ---
>> >> hw/virtio/virtio-pci.c | 2 ++
>> >> 1 file changed, 2 insertions(+)
>> >>
>> >> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
>> >> index ddb5da1..af937d2 100644
>> >> --- a/hw/virtio/virtio-pci.c
>> >> +++ b/hw/virtio/virtio-pci.c
>> >> @@ -320,6 +320,8 @@ static void virtio_ioport_write(void *opaque,
>> >> uint32_t addr, uint32_t val)
>> >> if ((val & VIRTIO_CONFIG_S_DRIVER_OK) &&
>> >> !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
>> >> proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
>> >> +
>> >> memory_region_set_enabled(&proxy->pci_dev.bus_master_enable_region,
>> >> + true);
>> >> }
>> >> break;
>> >> case VIRTIO_MSI_CONFIG_VECTOR:
>> >
>> > Cc'ing Alexey for some SLOF and early boot of the ppc64 kernel expertise.
>> >
>> > Michael,
>> >
>> > This was enough to fix virtio-net in the rhel6.5 x86 guest case.
>> > Unfortunately,
>> > this fails for rhel6.5 ppc64 because it is never called...
>>
>> > 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.
In SLOF, we do enable PCI MASTER during device scanning and then later
disable it.
Regards
Nikunj
