Re: [RFC PATCH 02/12] virtio/s390: DMA support for virtio-ccw

[Halil Pasic <pasic@linux.ibm.com>]

On Tue, 9 Apr 2019 11:57:43 +0200
Cornelia Huck <cohuck@redhat.com> wrote:

> On Fri,  5 Apr 2019 01:16:12 +0200
> Halil Pasic <pasic@linux.ibm.com> wrote:
> 
> > Currently we have a problem if a virtio-ccw device has
> > VIRTIO_F_IOMMU_PLATFORM. 
> 
> Can you please describe what the actual problem is?
> 

Without this patch:

WARNING: CPU: 2 PID: 26
at [..]/kernel/dma/mapping.c:251
dma_alloc_attrs+0x8e/0xd0 Modules linked in: CPU: 2 PID: 26 Comm:
kworker/u6:1 Not tainted 5.1.0-rc3-00023-g1ec89ec #596 Hardware name:
IBM 2964 NC9 712 (KVM/Linux) Workqueue: events_unbound async_run_entry_fn
Krnl PSW : 0704c00180000000 000000000021b18e (dma_alloc_attrs+0x8e/0xd0)
           R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
Krnl GPRS: 0000000000000000 0000000000000000 0000000000000000
0000000000001406 000003e00040f838 0000000000002dc0 0000000000000100
0000000000000001 0000000000001000 000000000236f028 000003e00040f838
0000000000001406 000000004b289828 0000000000000080 000003e00040f6f8
000003e00040f6a0 Krnl Code: 000000000021b17e: f0e00004ebaf
srp	4(15,%r0),2991(%r14),0 000000000021b184: f0c0000407f4
srp	4(13,%r0),2036,0 #000000000021b18a: a7f40001
brc	15,21b18c >000000000021b18e: ec5520bc0055	risbg
%r5,%r5,32,188,0 000000000021b194: b9020011		ltgr
%r1,%r1 000000000021b198: a784ffd9		brc	8,21b14a
           000000000021b19c: e31010000002	ltg	%r1,0(%r1)
           000000000021b1a2: a7840012		brc	8,21b1c6
Call Trace:
([<0000000000000004>] 0x4)
 [<00000000007a7d54>] vring_alloc_queue+0x74/0x90 
 [<00000000007a8390>] vring_create_virtqueue+0xf8/0x288 
 [<0000000000919ec0>] virtio_ccw_find_vqs+0xf8/0x950 
 [<000000000080772e>] init_vq+0x16e/0x318 
 [<00000000008087c4>] virtblk_probe+0xf4/0xb58 
 [<00000000007a62a6>] virtio_dev_probe+0x1a6/0x250 
 [<00000000007ea498>] really_probe+0x1c8/0x290 
 [<00000000007ea746>] driver_probe_device+0x86/0x160 
 [<00000000007e7cba>] bus_for_each_drv+0x7a/0xc0 
 [<00000000007ea23c>] __device_attach+0xfc/0x180 
 [<00000000007e9116>] bus_probe_device+0xae/0xc8 
 [<00000000007e5066>] device_add+0x3fe/0x698 
 [<00000000007a5d92>] register_virtio_device+0xca/0x120 
 [<00000000009195a2>] virtio_ccw_online+0x1b2/0x220 
 [<000000000089853e>] ccw_device_set_online+0x1d6/0x4d8 
 [<0000000000918cf6>] virtio_ccw_auto_online+0x26/0x58 
 [<00000000001a61b6>] async_run_entry_fn+0x5e/0x158 
 [<0000000000199322>] process_one_work+0x25a/0x668 
 [<000000000019977a>] worker_thread+0x4a/0x428 
 [<00000000001a1ae8>] kthread+0x150/0x170 
 [<0000000000aeab3a>] kernel_thread_starter+0x6/0xc 
 [<0000000000aeab34>] kernel_thread_starter+0x0/0xc 

[..]

virtio_ccw 0.0.0301: no vq
---[ end trace d35815958c12cad3 ]---
virtio_ccw 0.0.0300: no vq
virtio_blk: probe of virtio1 failed with error -12
virtio_blk: probe of virtio3 failed with error -12

Means virtio devices broken.

Should I
s/we have a problem if a virtio-ccw device/virtio-ccw devices do not work if the device/
?

> > In future we do want to support DMA API with
> > virtio-ccw.
> > 
> > Let us do the plumbing, so the feature VIRTIO_F_IOMMU_PLATFORM works
> > with virtio-ccw.
> > 
> > Let us also switch from legacy avail/used accessors to the DMA aware
> > ones (even if it isn't strictly necessary).
> 
> I think with this change we can remove the legacy accessors, if I
> didn't mis-grep.
> 

That is possible, I can do that in v1.

> > 
> > Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> > ---
> >  drivers/s390/virtio/virtio_ccw.c | 23 +++++++++++++++++------
> >  1 file changed, 17 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> > index edf4afe2d688..5956c9e820bb 100644
> > --- a/drivers/s390/virtio/virtio_ccw.c
> > +++ b/drivers/s390/virtio/virtio_ccw.c
> > @@ -66,6 +66,7 @@ struct virtio_ccw_device {
> >  	bool device_lost;
> >  	unsigned int config_ready;
> >  	void *airq_info;
> > +	__u64 dma_mask;
> 
> u64?
> 

Right, has nothing to do with userspace.

> >  };
> >  
> >  struct vq_info_block_legacy {
> > @@ -536,8 +537,8 @@ static struct virtqueue *virtio_ccw_setup_vq(struct virtio_device *vdev,
> >  		info->info_block->s.desc = queue;
> >  		info->info_block->s.index = i;
> >  		info->info_block->s.num = info->num;
> > -		info->info_block->s.avail = (__u64)virtqueue_get_avail(vq);
> > -		info->info_block->s.used = (__u64)virtqueue_get_used(vq);
> > +		info->info_block->s.avail = (__u64)virtqueue_get_avail_addr(vq);
> > +		info->info_block->s.used = (__u64)virtqueue_get_used_addr(vq);
> >  		ccw->count = sizeof(info->info_block->s);
> >  	}
> >  	ccw->cmd_code = CCW_CMD_SET_VQ;
> > @@ -769,10 +770,8 @@ static u64 virtio_ccw_get_features(struct virtio_device *vdev)
> >  static void ccw_transport_features(struct virtio_device *vdev)
> >  {
> >  	/*
> > -	 * Packed ring isn't enabled on virtio_ccw for now,
> > -	 * because virtio_ccw uses some legacy accessors,
> > -	 * e.g. virtqueue_get_avail() and virtqueue_get_used()
> > -	 * which aren't available in packed ring currently.
> > +	 * There shouldn't be anything that precludes supporting paced.
> 
> s/paced/packed/

Thx!

> 
> > +	 * TODO: Remove the limitation after having another look into this.
> >  	 */
> >  	__virtio_clear_bit(vdev, VIRTIO_F_RING_PACKED);
> >  }
> > @@ -1255,6 +1254,18 @@ static int virtio_ccw_online(struct ccw_device *cdev)
> >  		ret = -ENOMEM;
> >  		goto out_free;
> >  	}
> > +	vcdev->vdev.dev.parent = &cdev->dev;
> 
> That one makes sense, pci and mmio are doing that as well.
> 
> > +	cdev->dev.dma_mask = &vcdev->dma_mask;
> 
> That one feels a bit weird. Will this change in one of the follow-on
> patches? (Have not yet looked at the whole series.)

I don't thinks so. Do you mean this should happen within the cio code?
I think I started out with the idea to keep the scope as narrow as
possible. Do you have any suggestions?

> 
> > +
> > +	ret = dma_set_mask_and_coherent(&cdev->dev, DMA_BIT_MASK(64));
> > +	if (ret)
> > +		ret = dma_set_mask_and_coherent(&cdev->dev,
> > +						DMA_BIT_MASK(32));
> > +	if (ret) {
> > +		dev_warn(&cdev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
> 
> This does not look like you'd try to continue?
> 

I remember now. First I did continue, then I changed this to fail hard
so I can not ignore any such problems while smoke testing ('I don't always
check the kernel messages'), but kept the old message. This basically
should not fail anyway, otherwise we have a problem AFAIU.

By the way virtio-pci tries to continue indeed, and this is also where
the wording comes from ;).

What would you prefer? Try to continue or fail right away?

Regards,
Halil

> > +		goto out_free;
> > +	}
> > +
> >  	vcdev->config_block = kzalloc(sizeof(*vcdev->config_block),
> >  				   GFP_DMA | GFP_KERNEL);
> >  	if (!vcdev->config_block) {
>