Re: [PATCH v4 10/25] virtio: add API to enable VQs early

From: Andy Grover
Date: Mon Nov 10 2014 - 19:45:34 EST

On 10/13/2014 12:50 AM, Michael S. Tsirkin wrote:
virtio spec 0.9.X requires DRIVER_OK to be set before
VQs are used, but some drivers use VQs before probe
function returns.
Since DRIVER_OK is set after probe, this violates the spec.

Even though under virtio 1.0 transitional devices support this
behaviour, we want to make it possible for those early callers to become
spec compliant and eventually support non-transitional devices.

Add API for drivers to call before using VQs.

Sets DRIVER_OK internally.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Reviewed-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
---
include/linux/virtio_config.h | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index e8f8f71..e36403b 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -109,6 +109,23 @@ struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
return vq;
}

+/**
+ * virtio_device_ready - enable vq use in probe function
+ * @vdev: the device
+ *
+ * Driver must call this to use vqs in the probe function.
+ *
+ * Note: vqs are enabled automatically after probe returns.
+ */
+static inline
+void virtio_device_ready(struct virtio_device *dev)
+{
+ unsigned status = dev->config->get_status(dev);
+
+ BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
+ dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
+}

Getting a BUG when booting via KVM, host Fedora 20, guest Fedora 20.

my config is at:

https://fedorapeople.org/~grover/config-20141110



[ 0.828494] ------------[ cut here ]------------
[ 0.829039] kernel BUG at /home/agrover/git/kernel/include/linux/virtio_config.h:125!
[ 0.831266] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
[ 0.831266] Modules linked in:
[ 0.831266] CPU: 1 PID: 30 Comm: kworker/1:1 Not tainted 3.18.0-rc4 #120
[ 0.831266] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 0.831266] Workqueue: events control_work_handler
[ 0.831266] task: ffff88003cd98000 ti: ffff88003cd94000 task.ti: ffff88003cd94000
[ 0.831266] RIP: 0010:[<ffffffff81445004>] [<ffffffff81445004>] add_port+0x264/0x410
[ 0.831266] RSP: 0000:ffff88003cd97c78 EFLAGS: 00010202
[ 0.831266] RAX: 0000000000000007 RBX: ffff88003c58c400 RCX: 0000000000000001
[ 0.831266] RDX: 000000000000c132 RSI: ffffffff81a955e9 RDI: 000000000001c132
[ 0.831266] RBP: ffff88003cd97cc8 R08: 0000000000000000 R09: 0000000000000000
[ 0.831266] R10: 0000000000000001 R11: 0000000000000000 R12: ffff88003c58be00
[ 0.831266] R13: 0000000000000001 R14: ffff8800395ca800 R15: ffff88003c58c420
[ 0.831266] FS: 0000000000000000(0000) GS:ffff88003fa00000(0000) knlGS:0000000000000000
[ 0.831266] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 0.831266] CR2: 0000000000000000 CR3: 0000000001c11000 CR4: 00000000000006e0
[ 0.831266] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.831266] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.831266] Stack:
[ 0.831266] ffff880000000001 0000000000000292 0000000000000000 0000000000000001
[ 0.831266] ffff88003cd97cc8 ffff88003dfa8a20 ffff88003c58beb8 ffff88003c58be10
[ 0.831266] ffff8800395a2000 0000000000000000 ffff88003cd97d38 ffffffff8144531a
[ 0.831266] Call Trace:
[ 0.831266] [<ffffffff8144531a>] control_work_handler+0x16a/0x3c0
[ 0.831266] [<ffffffff8108b0c8>] ? process_one_work+0x208/0x500
[ 0.831266] [<ffffffff8108b16c>] process_one_work+0x2ac/0x500
[ 0.831266] [<ffffffff8108b0c8>] ? process_one_work+0x208/0x500
[ 0.831266] [<ffffffff8108b68e>] worker_thread+0x2ce/0x4e0
[ 0.831266] [<ffffffff8108b3c0>] ? process_one_work+0x500/0x500
[ 0.831266] [<ffffffff81090b28>] kthread+0xf8/0x100
[ 0.831266] [<ffffffff810bad7d>] ? trace_hardirqs_on+0xd/0x10
[ 0.831266] [<ffffffff81090a30>] ? kthread_stop+0x140/0x140
[ 0.831266] [<ffffffff816ea92c>] ret_from_fork+0x7c/0xb0
[ 0.831266] [<ffffffff81090a30>] ? kthread_stop+0x140/0x140
[ 0.831266] Code: c7 c2 48 31 01 83 48 c7 c6 e9 55 a9 81 e8 55 b4 c6 ff 4d 8b b4 24 58 01 00 00 49 8b 86 e8 04 00 00 4c 89 f7 ff 50 10 a8 04 74 0c <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 49 8b 96 e8 04 00 00 83 c8
[ 0.831266] RIP [<ffffffff81445004>] add_port+0x264/0x410
[ 0.831266] RSP <ffff88003cd97c78>
[ 0.878202] ---[ end trace f98fbb172cc7bbf4 ]---

Thanks -- Andy

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