Re: [PATCH 04/20] virtio: Implement get_shm_region for PCI transport

[Stefan Hajnoczi]

On Tue, Mar 10, 2020 at 02:19:36PM -0400, Vivek Goyal wrote:
> On Tue, Mar 10, 2020 at 11:04:37AM +0000, Stefan Hajnoczi wrote:
> > On Wed, Mar 04, 2020 at 11:58:29AM -0500, Vivek Goyal wrote:
> > > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> > > index 7abcc50838b8..52f179411015 100644
> > > --- a/drivers/virtio/virtio_pci_modern.c
> > > +++ b/drivers/virtio/virtio_pci_modern.c
> > > @@ -443,6 +443,111 @@ static void del_vq(struct virtio_pci_vq_info *info)
> > >  	vring_del_virtqueue(vq);
> > >  }
> > >  
> > > +static int virtio_pci_find_shm_cap(struct pci_dev *dev,
> > > +                                   u8 required_id,
> > > +                                   u8 *bar, u64 *offset, u64 *len)
> > > +{
> > > +	int pos;
> > > +
> > > +        for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR);
> > 
> > Please fix the mixed tabs vs space indentation in this patch.
> 
> Will do. There are plenty of these in this patch.
> 
> > 
> > > +static bool vp_get_shm_region(struct virtio_device *vdev,
> > > +			      struct virtio_shm_region *region, u8 id)
> > > +{
> > > +	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> > > +	struct pci_dev *pci_dev = vp_dev->pci_dev;
> > > +	u8 bar;
> > > +	u64 offset, len;
> > > +	phys_addr_t phys_addr;
> > > +	size_t bar_len;
> > > +	int ret;
> > > +
> > > +	if (!virtio_pci_find_shm_cap(pci_dev, id, &bar, &offset, &len)) {
> > > +		return false;
> > > +	}
> > > +
> > > +	ret = pci_request_region(pci_dev, bar, "virtio-pci-shm");
> > > +	if (ret < 0) {
> > > +		dev_err(&pci_dev->dev, "%s: failed to request BAR\n",
> > > +			__func__);
> > > +		return false;
> > > +	}
> > > +
> > > +	phys_addr = pci_resource_start(pci_dev, bar);
> > > +	bar_len = pci_resource_len(pci_dev, bar);
> > > +
> > > +        if (offset + len > bar_len) {
> > > +                dev_err(&pci_dev->dev,
> > > +                        "%s: bar shorter than cap offset+len\n",
> > > +                        __func__);
> > > +                return false;
> > > +        }
> > > +
> > > +	region->len = len;
> > > +	region->addr = (u64) phys_addr + offset;
> > > +
> > > +	return true;
> > > +}
> > 
> > Missing pci_release_region()?
> 
> Good catch. We don't have a mechanism to call pci_relese_region() and 
> virtio-mmio device's ->get_shm_region() implementation does not even
> seem to reserve the resources.
> 
> So how about we leave this resource reservation to the caller.
> ->get_shm_region() just returns the addr/len pair of requested resource.
> 
> Something like this patch.
> 
> ---
>  drivers/virtio/virtio_pci_modern.c |    8 --------
>  fs/fuse/virtio_fs.c                |   13 ++++++++++---
>  2 files changed, 10 insertions(+), 11 deletions(-)
> 
> Index: redhat-linux/fs/fuse/virtio_fs.c
> ===================================================================
> --- redhat-linux.orig/fs/fuse/virtio_fs.c	2020-03-10 09:13:34.624565666 -0400
> +++ redhat-linux/fs/fuse/virtio_fs.c	2020-03-10 14:11:10.970284651 -0400
> @@ -763,11 +763,18 @@ static int virtio_fs_setup_dax(struct vi
>  	if (!have_cache) {
>  		dev_notice(&vdev->dev, "%s: No cache capability\n", __func__);
>  		return 0;
> -	} else {
> -		dev_notice(&vdev->dev, "Cache len: 0x%llx @ 0x%llx\n",
> -			   cache_reg.len, cache_reg.addr);
>  	}
>  
> +	if (!devm_request_mem_region(&vdev->dev, cache_reg.addr, cache_reg.len,
> +				     dev_name(&vdev->dev))) {
> +		dev_warn(&vdev->dev, "could not reserve region addr=0x%llx"
> +			 " len=0x%llx\n", cache_reg.addr, cache_reg.len);
> +		return -EBUSY;
> +        }
> +
> +	dev_notice(&vdev->dev, "Cache len: 0x%llx @ 0x%llx\n", cache_reg.len,
> +		   cache_reg.addr);
> +
>  	pgmap = devm_kzalloc(&vdev->dev, sizeof(*pgmap), GFP_KERNEL);
>  	if (!pgmap)
>  		return -ENOMEM;
> Index: redhat-linux/drivers/virtio/virtio_pci_modern.c
> ===================================================================
> --- redhat-linux.orig/drivers/virtio/virtio_pci_modern.c	2020-03-10 08:51:36.886565666 -0400
> +++ redhat-linux/drivers/virtio/virtio_pci_modern.c	2020-03-10 13:43:15.168753543 -0400
> @@ -511,19 +511,11 @@ static bool vp_get_shm_region(struct vir
>  	u64 offset, len;
>  	phys_addr_t phys_addr;
>  	size_t bar_len;
> -	int ret;
>  
>  	if (!virtio_pci_find_shm_cap(pci_dev, id, &bar, &offset, &len)) {
>  		return false;
>  	}
>  
> -	ret = pci_request_region(pci_dev, bar, "virtio-pci-shm");
> -	if (ret < 0) {
> -		dev_err(&pci_dev->dev, "%s: failed to request BAR\n",
> -			__func__);
> -		return false;
> -	}
> -
>  	phys_addr = pci_resource_start(pci_dev, bar);
>  	bar_len = pci_resource_len(pci_dev, bar);

Do pci_resource_start()/pci_resource_len() work on a BAR where
pci_request_region() hasn't been called yet?  (I haven't checked the
code, sorry...)

Assuming yes, then my next question is whether devm_request_mem_region()
works in both the VIRTIO PCI and MMIO cases?

If yes, then this looks like a solution, though the need for
devm_request_mem_region() should be explained in the vp_get_shm_region()
doc comments so that callers remember to make that call.  Or maybe it
can be included in vp_get_shm_region().

Stefan

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