From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53076) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XReY8-0007Lo-2M for qemu-devel@nongnu.org; Wed, 10 Sep 2014 05:50:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XReY3-0003zK-Ll for qemu-devel@nongnu.org; Wed, 10 Sep 2014 05:50:52 -0400 Date: Wed, 10 Sep 2014 13:54:01 +0300 From: "Michael S. Tsirkin" Message-ID: <20140910105401.GF7902@redhat.com> References: <1410192283-4026-1-git-send-email-mst@redhat.com> <20140910003532.22d72602@bahia.local> <87oaunops6.fsf@abhimanyu.in.ibm.com> <20140910093230.GB7902@redhat.com> <87k35bomyg.fsf@abhimanyu.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87k35bomyg.fsf@abhimanyu.in.ibm.com> Subject: Re: [Qemu-devel] [PATCH] virtio-pci: enable bus master for old guests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Nikunj A Dadhania Cc: Alexey Kardashevskiy , Jan Kiszka , qemu-stable@nongnu.org, qemu-devel@nongnu.org, Anthony Liguori On Wed, Sep 10, 2014 at 02:45:51PM +0530, Nikunj A Dadhania wrote: > "Michael S. Tsirkin" writes: > > > On Wed, Sep 10, 2014 at 01:44:49PM +0530, Nikunj A Dadhania wrote: > >> Greg Kurz writes: > >> > >> > On Mon, 8 Sep 2014 19:05:02 +0300 > >> > "Michael S. Tsirkin" 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-stable@nongnu.org > >> >> Reported-by: Greg Kurz > >> >> Signed-off-by: Jan Kiszka > >> >> Signed-off-by: Michael S. Tsirkin > >> >> --- > >> >> 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 But device is then reset, right Greg? You get as far as reset? If yes I doubt something that happens before reset matters, unless we are leaking some state across reset which would be a bug in itself.