Hi Paolo & Co,
So I've been running into another bug with SeaBIOS w/ virtio-scsi + vhost-scsi-pci code..
During the last weeks debugging on the QEMU vhost memory re-mapping bug, my seabios builds have been using a smaller target ID (16) for scanning than the default hard coded value of 256 in init_virtio_scsi().
After bumping this value back to 256 recently, a bogus out_num value from vhost_get_vq_desc() start appearing on the tcm_vhost side:
[17348.044031] Invalid buffer layout out: 0 in: 2
After adding more debug output to SeaBIOS, the vring->num value appears to be reset from the expected MAX_QUEUE_NUM=128, then incremented each time after vring_more_used() is called to poll for completion..
init virtio-scsi found virtio-scsi at 0:4 vring_init Setting vr->num: 128 Calling virtio_scsi_scan_target for target: 0 Searching bootorder for: /pci@i0cf8/*@4/*@0/*@0,0 virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 2 virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 128 vring_add_buf, vr: 0x000ed404 vr->num: 128 vring_add_buf, head: 0, index: 0 vring_add_buf, setting desc[prev=2].flags vring_add_buf, setting free_head: 3 vring_add_buf, setting q->vdata[head=0] vring_add_buf, setting q->ring[av=0] virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 128 virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 128 virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 1 ^^^^^^^^^^^^^^^^^^^^^^^^^
Reset from 128 to 1 immediate after first vring_more_used()..?
vring_get_buf last_used_idx: 0 vr: 0x000ed404 vr->num: 1 vring_get_buf checking &used->ring[0] vring_get_buf, using new last_unsed: 0 >>>>>>>>>>>>>>>>>> vring_get_buf using id: 0 from elem->id: 0x000ed004 vring_detach: vq->free_head: 3 vring_detach: Setting new vq->free_head: 0 virtio_scsi_cmd, after vring_get_buf #5 vr: 0x000ed404 vr->num: 1 Calling virtio_scsi_scan_target for target: 1 Searching bootorder for: /pci@i0cf8/*@4/*@0/*@1,0 virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 2 virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 1 vring_add_buf, vr: 0x000ed404 vr->num: 1 vring_add_buf, head: 0, index: 0 vring_add_buf, setting desc[prev=2].flags vring_add_buf, setting free_head: 3 vring_add_buf, setting q->vdata[head=0] vring_add_buf, setting q->ring[av=0] virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 1 virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 1 virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 2 ^^^^^^^^^^^^^^^^^^^^^^^^^
Incremented from 1 to 2 after second vring_more_used()..?
vring_get_buf last_used_idx: 1 vr: 0x000ed404 vr->num: 2 vring_get_buf checking &used->ring[1] vring_get_buf, using new last_unsed: 1 >>>>>>>>>>>>>>>>>> vring_get_buf using id: 0 from elem->id: 0x000ed00c vring_detach: vq->free_head: 3 vring_detach: Setting new vq->free_head: 0 virtio_scsi_cmd, after vring_get_buf #5 vr: 0x000ed404 vr->num: 2 virtio-scsi vendor='LIO-ORG' product='RAMDISK-MCP' rev='4.0' type=0 removable=0 virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 1 virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 2 vring_add_buf, vr: 0x000ed404 vr->num: 2 vring_add_buf, head: 0, index: 0 vring_add_buf, setting desc[prev=1].flags vring_add_buf, setting free_head: 2 vring_add_buf, setting q->vdata[head=0] vring_add_buf, setting q->ring[av=0] virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 2 virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 2 virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 3 ^^^^^^^^^^^^^^^^^^^^^^^^^
Incremented from 2 to 3, and so on..
and this keeps happening until vr->num begins to exceed MAX_QUEUE_NUM around scanning of target ID 127:
virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 128 virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 128 virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 129 vring_get_buf last_used_idx: 128 vr: 0x000ed404 vr->num: 129 vring_get_buf checking &used->ring[128] vring_get_buf, using new last_unsed: 128 >>>>>>>>>>>>>>>>>> vring_get_buf using id: 129 from elem->id: 0x000ed404 vring_detach: vq->free_head: 3 vring_detach: Setting new vq->free_head: 129 virtio_scsi_cmd, after vring_get_buf #5 vr: 0x000ed404 vr->num: 129 Calling virtio_scsi_scan_target for target: 127 Searching bootorder for: /pci@i0cf8/*@4/*@0/*@127,0 virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 2 virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 129 vring_add_buf, vr: 0x000ed404 vr->num: 129 vring_add_buf, head: 129, index: 0 vring_add_buf, setting desc[prev=4].flags vring_add_buf, setting free_head: 5 vring_add_buf, setting q->vdata[head=0] vring_add_buf, setting q->ring[av=129] virtio_scsi_cmd, after vring_add_buf vr: 0x000ed404 vr->num: 129 virtio_scsi_cmd, after vring_kick vr: 0x000ed404 vr->num: 129 virtio_scsi_cmd, after vring_more_used #4 vr: 0x000ed404 vr->num: 130 vring_get_buf last_used_idx: 129 vr: 0x000ed404 vr->num: 130 vring_get_buf checking &used->ring[129] vring_get_buf, using new last_unsed: 129 >>>>>>>>>>>>>>>>>> vring_get_buf using id: 968704 from elem->id: 0x000ed40c vring_detach: vq->free_head: 5 vring_detach: Setting new vq->free_head: 968704 virtio_scsi_cmd, after vring_get_buf #5 vr: 0x000ed404 vr->num: 130 Calling virtio_scsi_scan_target for target: 128 Searching bootorder for: /pci@i0cf8/*@4/*@0/*@128,0 virtio_scsi_cmd, using vring_add_buf for out_num: 1 in_num: 2 virtio_scsi_cmd, using vring_add_buf vr: 0x000ed404 vr->num: 130 vring_add_buf, vr: 0x000ed404 vr->num: 130 vring_add_buf, head: 51200, index: 0 vring_add_buf, setting desc[prev=1].flags vring_add_buf, setting free_head: 2 vring_add_buf, setting q->vdata[head=0] vring_add_buf, setting q->ring[av=51200]
until '[17348.044031] Invalid buffer layout out: 0 in: 2' appears on the vhost.
So it's clear this definitely is not supposed to be happening, but I've not yet been able to ascertain why it's suddenly being triggered now..? I don't recall Asias running into a similar issue during his earlier testing, but this bug is happening after every I/O in SeaBIOS with the most recent vhost-scsi-pci code.
I'm using the following to work-around this issue for the moment, and would like some input from virtio / SeaBIOS folks..
WDYT..?
--nab
diff --git a/src/virtio-ring.c b/src/virtio-ring.c index bddb090..e046141 100644 --- a/src/virtio-ring.c +++ b/src/virtio-ring.c @@ -35,10 +35,16 @@
int vring_more_used(struct vring_virtqueue *vq) { + struct vring *vr = &vq->vring; struct vring_used *used = GET_LOWFLAT(vq->vring.used); int more = GET_LOWFLAT(vq->last_used_idx) != GET_LOWFLAT(used->idx); /* Make sure ring reads are done after idx read above. */ smp_rmb(); + + /* Huh..? vr->num is somehow changing from below us..? */ + if (GET_LOWFLAT(vr->num) != MAX_QUEUE_NUM) { + SET_LOWFLAT(vr->num, MAX_QUEUE_NUM); + } return more; }