linux/drivers/virtio, branch v2.6.26

virtio: Complete feature negotation before updating status

2008-06-15T20:46:16Z

lguest (in rusty's use-tun-ringfd patch) assumes that the guest has updated its feature bits before setting its status to VIRTIO_CONFIG_S_DRIVER_OK. That's pretty reasonable, so let's make it so. Signed-off-by: Mark McLoughlin Signed-off-by: Rusty Russell Signed-off-by: Linus Torvalds

virtio: force callback on empty.

2008-05-30T05:09:46Z

virtio allows drivers to suppress callbacks (ie. interrupts) for efficiency (no locking, it's just an optimization). There's a similar mechanism for the host to suppress notifications coming from the guest: in that case, we ignore the suppression if the ring is completely full. It turns out that life is simpler if the host similarly ignores callback suppression when the ring is completely empty: the network driver wants to free up old packets in a timely manner, and otherwise has to use a timer to poll. We have to remove the code which ignores interrupts when the driver has disabled them (again, it had no locking and hence was unreliable anyway). Signed-off-by: Rusty Russell

virtio_net: another race with virtio_net and enable_cb

2008-05-30T05:09:45Z

Hello Rusty, seems that we still have a problem with virtio_net and the enable_cb callback. During a long running network stress tests with virtio and got the following oops: ------------[ cut here ]------------ kernel BUG at drivers/virtio/virtio_ring.c:230! illegal operation: 0001 [#1] SMP Modules linked in: CPU: 0 Not tainted 2.6.26-rc2-kvm-00436-gc94c08b-dirty #34 Process netserver (pid: 2582, task: 000000000fbc4c68, ksp: 000000000f42b990) Krnl PSW : 0704c00180000000 00000000002d0ec8 (vring_enable_cb+0x1c/0x60) R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 EA:3 Krnl GPRS: 0000000000000000 0000000000000000 000000000ef3d000 0000000010009800 0000000000000000 0000000000419ce0 0000000000000080 000000000000007b 000000000adb5538 000000000ef40900 000000000ef40000 000000000ef40920 0000000000000000 0000000000000005 000000000029c1b0 000000000fea7d18 Krnl Code: 00000000002d0ebc: a7110001 tmll %r1,1 00000000002d0ec0: a7740004 brc 7,2d0ec8 00000000002d0ec4: a7f40001 brc 15,2d0ec6 >00000000002d0ec8: a517fffe nill %r1,65534 00000000002d0ecc: 40103000 sth %r1,0(%r3) 00000000002d0ed0: 07f0 bcr 15,%r0 00000000002d0ed2: e31020380004 lg %r1,56(%r2) 00000000002d0ed8: a7480000 lhi %r4,0 Call Trace: ([<000000000029c0fc>] virtnet_poll+0x290/0x3b8) [<0000000000333fb8>] net_rx_action+0x9c/0x1b8 [<00000000001394bc>] __do_softirq+0x74/0x108 [<000000000010d16a>] do_softirq+0x92/0xac [<0000000000139826>] irq_exit+0x72/0xc8 [<000000000010a7b6>] do_extint+0xe2/0x104 [<0000000000110508>] ext_no_vtime+0x16/0x1a Last Breaking-Event-Address: [<00000000002d0ec4>] vring_enable_cb+0x18/0x60 I looked into the virtio_net code for some time and I think the following scenario happened. Please look at virtnet_poll: [...] /* Out of packets? */ if (received < budget) { netif_rx_complete(vi->dev, napi); if (unlikely(!vi->rvq->vq_ops->enable_cb(vi->rvq)) && napi_schedule_prep(napi)) { vi->rvq->vq_ops->disable_cb(vi->rvq); __netif_rx_schedule(vi->dev, napi); goto again; } } If an interrupt arrives after netif_rx_complete, a second poll routine can run on a different cpu. The second check for napi_schedule_prep would prevent any harm in the network stack, but we have called enable_cb possibly after the disable_cb in skb_recv_done. static void skb_recv_done(struct virtqueue *rvq) { struct virtnet_info *vi = rvq->vdev->priv; /* Schedule NAPI, Suppress further interrupts if successful. */ if (netif_rx_schedule_prep(vi->dev, &vi->napi)) { rvq->vq_ops->disable_cb(rvq); __netif_rx_schedule(vi->dev, &vi->napi); } } That means that the second poll routine runs with interrupts enabled, which is ok, since we can handle additional interrupts. The problem is now that the second poll routine might also call enable_cb, triggering the BUG. The only solution I can come up with, is to remove the BUG statement in enable_cb - similar to disable_cb. Opinions or better ideas where the oops could come from? Signed-off-by: Christian Borntraeger Signed-off-by: Rusty Russell

virtio: set device index in common code.

2008-05-30T05:09:42Z

Anthony Liguori points out that three different transports use the virtio code, but each one keeps its own counter to set the virtio_device's index field. In theory (though not in current practice) this means that names could be duplicated, and that risk grows as more transports are created. So we move the selection of the unique virtio_device.index into the common code in virtio.c, which has the side-benefit of removing duplicate code. The only complexity is that lguest and S/390 use the index to uniquely identify the device in case of catastrophic failure before register_virtio_device() is called: now we use the offset within the descriptor page as a unique identifier for the printks. Signed-off-by: Rusty Russell Cc: Christian Borntraeger Cc: Martin Schwidefsky Cc: Carsten Otte Cc: Heiko Carstens Cc: Chris Lalancette Cc: Anthony Liguori

virtio: virtio_pci should not set bus_id.

2008-05-30T05:09:42Z

The common virtio code sets the bus_id, overriding anything virtio_pci sets anyway. Signed-off-by: Rusty Russell Cc: Christian Borntraeger Cc: Martin Schwidefsky Cc: Carsten Otte Cc: Heiko Carstens Cc: Chris Lalancette Cc: Anthony Liguori

virtio: bus_id for devices should contain 'virtio'

2008-05-30T05:09:42Z

Chris Lalancette points out that virtio.c sets all device names to '0', '1', etc, which looks silly in /proc/interrupts. We change this from '%d' to 'virtio%d'. Signed-off-by: Rusty Russell Cc: Christian Borntraeger Cc: Martin Schwidefsky Cc: Carsten Otte Cc: Heiko Carstens Cc: Chris Lalancette Cc: Anthony Liguori

virtio: explicit advertisement of driver features

2008-05-02T11:50:50Z

A recent proposed feature addition to the virtio block driver revealed some flaws in the API: in particular, we assume that feature negotiation is complete once a driver's probe function returns. There is nothing in the API to require this, however, and even I didn't notice when it was violated. So instead, we require the driver to specify what features it supports in a table, we can then move the feature negotiation into the virtio core. The intersection of device and driver features are presented in a new 'features' bitmap in the struct virtio_device. Note that this highlights the difference between Linux unsigned-long bitmaps where each unsigned long is in native endian, and a straight-forward little-endian array of bytes. Drivers can still remove feature bits in their probe routine if they really have to. API changes: - dev->config->feature() no longer gets and acks a feature. - drivers should advertise their features in the 'feature_table' field - use virtio_has_feature() for extra sanity when checking feature bits Signed-off-by: Rusty Russell

virtio: change config to guest endian.

2008-05-02T11:50:50Z

A recent proposed feature addition to the virtio block driver revealed some flaws in the API, in particular how easy it is to break big endian machines. The virtio config space was originally chosen to be little-endian, because we thought the config might be part of the PCI config space for virtio_pci. It's actually a separate mmio region, so that argument holds little water; as only x86 is currently using the virtio mechanism, we can change this (but must do so now, before the impending s390 merge). API changes: - __virtio_config_val() just becomes a striaght vdev->config_get() call. Signed-off-by: Rusty Russell

virtio: fix sparse return void-valued expression warnings

2008-05-02T11:50:44Z

drivers/virtio/virtio_pci.c:148:2: warning: returning void-valued expression drivers/virtio/virtio_pci.c:155:2: warning: returning void-valued expression Signed-off-by: Harvey Harrison Signed-off-by: Rusty Russell

virtio: ignore corrupted virtqueues rather than spinning.

2008-05-02T11:50:43Z

A corrupt virtqueue (caused by the other end screwing up) can have strange results such as a driver spinning: just bail when we try to get a buffer from a known-broken queue. Signed-off-by: Rusty Russell