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