Re: [Qemu-devel] [PATCH v5 2/5] virtio-pmem: Add virtio pmem driver

[Pankaj Gupta]

> > 
> > > This patch adds virtio-pmem driver for KVM guest.
> > > 
> > > Guest reads the persistent memory range information from
> > > Qemu over VIRTIO and registers it on nvdimm_bus. It also
> > > creates a nd_region object with the persistent memory
> > > range information so that existing 'nvdimm/pmem' driver
> > > can reserve this into system memory map. This way
> > > 'virtio-pmem' driver uses existing functionality of pmem
> > > driver to register persistent memory compatible for DAX
> > > capable filesystems.
> > > 
> > > This also provides function to perform guest flush over
> > > VIRTIO from 'pmem' driver when userspace performs flush
> > > on DAX memory range.
> > > 
> > > Signed-off-by: Pankaj Gupta <address@hidden>
> > > ---
> > >  drivers/nvdimm/virtio_pmem.c     |  88 ++++++++++++++++++++++
> > >  drivers/virtio/Kconfig           |  10 +++
> > >  drivers/virtio/Makefile          |   1 +
> > >  drivers/virtio/pmem.c            | 124 +++++++++++++++++++++++++++++++
> > >  include/linux/virtio_pmem.h      |  60 +++++++++++++++
> > >  include/uapi/linux/virtio_ids.h  |   1 +
> > >  include/uapi/linux/virtio_pmem.h |  10 +++
> > >  7 files changed, 294 insertions(+)
> > >  create mode 100644 drivers/nvdimm/virtio_pmem.c
> > >  create mode 100644 drivers/virtio/pmem.c
> > >  create mode 100644 include/linux/virtio_pmem.h
> > >  create mode 100644 include/uapi/linux/virtio_pmem.h
> > > 
> > (...)
> > > diff --git a/drivers/virtio/pmem.c b/drivers/virtio/pmem.c
> > > new file mode 100644
> > > index 000000000000..cc9de9589d56
> > > --- /dev/null
> > > +++ b/drivers/virtio/pmem.c
> > > @@ -0,0 +1,124 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * virtio_pmem.c: Virtio pmem Driver
> > > + *
> > > + * Discovers persistent memory range information
> > > + * from host and registers the virtual pmem device
> > > + * with libnvdimm core.
> > > + */
> > > +#include <linux/virtio_pmem.h>
> > > +#include <../../drivers/nvdimm/nd.h>
> > > +
> > > +static struct virtio_device_id id_table[] = {
> > > + { VIRTIO_ID_PMEM, VIRTIO_DEV_ANY_ID },
> > > + { 0 },
> > > +};
> > > +
> > > + /* Initialize virt queue */
> > > +static int init_vq(struct virtio_pmem *vpmem)
> > 
> > IMHO, you don't gain much by splitting off this function...
> 
> It make sense to have all the vq-init-related stuff in one function, so
> here pmem_lock and req_list are used only for the vq.

Yes.

> Saying that - maybe it would be better to have the 3 in one struct.
> 
> > 
> > > +{
> > > + struct virtqueue *vq;
> > > +
> > > + /* single vq */
> > > + vpmem->req_vq = vq = virtio_find_single_vq(vpmem->vdev,
> > > +                         host_ack, "flush_queue");
> > > + if (IS_ERR(vq))
> > > +         return PTR_ERR(vq);
> > 
> > I'm personally not a fan of chained assignments... I think I'd just
> > drop the 'vq' variable and operate on vpmem->req_vq directly.
> 
> +1

Will drop extra vq.

> 
> > 
> > > +
> > > + spin_lock_init(&vpmem->pmem_lock);
> > > + INIT_LIST_HEAD(&vpmem->req_list);
> > > +
> > > + return 0;
> > > +};
> > > +
> > > +static int virtio_pmem_probe(struct virtio_device *vdev)
> > > +{
> > > + int err = 0;
> > > + struct resource res;
> > > + struct virtio_pmem *vpmem;
> > > + struct nvdimm_bus *nvdimm_bus;
> > > + struct nd_region_desc ndr_desc = {};
> > > + int nid = dev_to_node(&vdev->dev);
> > > + struct nd_region *nd_region;
> > > +
> > > + if (!vdev->config->get) {
> > > +         dev_err(&vdev->dev, "%s failure: config disabled\n",
> > 
> > Maybe s/config disabled/config access disabled/ ? That seems to be the
> > more common message.
> > 
> > > +                 __func__);
> > > +         return -EINVAL;
> > > + }
> > > +
> > > + vdev->priv = vpmem = devm_kzalloc(&vdev->dev, sizeof(*vpmem),
> > > +                                 GFP_KERNEL);
> > 
> > Here, the vpmem variable makes sense for convenience, but I'm again not
> > a fan of the chaining :)
> 
> +1

here as well.

> 
> > 
> > > + if (!vpmem) {
> > > +         err = -ENOMEM;
> > > +         goto out_err;
> > > + }
> > > +
> > > + vpmem->vdev = vdev;
> > > + err = init_vq(vpmem);
> > > + if (err)
> > > +         goto out_err;
> > > +
> > > + virtio_cread(vpmem->vdev, struct virtio_pmem_config,
> > > +                 start, &vpmem->start);
> > > + virtio_cread(vpmem->vdev, struct virtio_pmem_config,
> > > +                 size, &vpmem->size);
> > > +
> > > + res.start = vpmem->start;
> > > + res.end   = vpmem->start + vpmem->size-1;
> > > + vpmem->nd_desc.provider_name = "virtio-pmem";
> > > + vpmem->nd_desc.module = THIS_MODULE;
> > > +
> > > + vpmem->nvdimm_bus = nvdimm_bus = nvdimm_bus_register(&vdev->dev,
> > > +                                         &vpmem->nd_desc);
> > 
> > And here :)
> > 
> > > + if (!nvdimm_bus)
> > > +         goto out_vq;
> > > +
> > > + dev_set_drvdata(&vdev->dev, nvdimm_bus);
> > > +
> > > + ndr_desc.res = &res;
> > > + ndr_desc.numa_node = nid;
> > > + ndr_desc.flush = virtio_pmem_flush;
> > > + set_bit(ND_REGION_PAGEMAP, &ndr_desc.flags);
> > > + set_bit(ND_REGION_ASYNC, &ndr_desc.flags);
> > > + nd_region = nvdimm_pmem_region_create(nvdimm_bus, &ndr_desc);
> > > + nd_region->provider_data =  dev_to_virtio
> > > +                                 (nd_region->dev.parent->parent);
> > 
> > Isn't it clear that this parent chain will always end up at &vdev->dev?
> > Maybe simply set ->provider_data to vdev directly? (Does it need to
> > grab a reference count of the device, BTW?)
> > 
> > > +
> > > + if (!nd_region)
> > > +         goto out_nd;
> > 
> > Probably better to do this check before you access nd_region's
> > members :)
> > 
> > > +
> > > + return 0;
> > > +out_nd:
> > > + err = -ENXIO;
> > > + nvdimm_bus_unregister(nvdimm_bus);
> > > +out_vq:
> > > + vdev->config->del_vqs(vdev);
> > > +out_err:
> > > + dev_err(&vdev->dev, "failed to register virtio pmem memory\n");
> > > + return err;
> > > +}
> > > +
> > > +static void virtio_pmem_remove(struct virtio_device *vdev)
> > > +{
> > > + struct virtio_pmem *vpmem = vdev->priv;
> > > + struct nvdimm_bus *nvdimm_bus = dev_get_drvdata(&vdev->dev);
> > > +
> > > + nvdimm_bus_unregister(nvdimm_bus);
> > 
> > I haven't followed this around the nvdimm code, but is the nd_region
> > you created during probe cleaned up automatically, or would you need to
> > do something here?
> > 
> > > + vdev->config->del_vqs(vdev);
> > > + vdev->config->reset(vdev);
> > > + kfree(vpmem);
> > 
> > You allocated vpmem via devm_kzalloc; isn't it freed automatically on
> > remove?
> > 
> > > +}
> > > +
> > > +static struct virtio_driver virtio_pmem_driver = {
> > > + .driver.name            = KBUILD_MODNAME,
> > > + .driver.owner           = THIS_MODULE,
> > > + .id_table               = id_table,
> > > + .probe                  = virtio_pmem_probe,
> > > + .remove                 = virtio_pmem_remove,
> > > +};
> > > +
> > > +module_virtio_driver(virtio_pmem_driver);
> > > +MODULE_DEVICE_TABLE(virtio, id_table);
> > > +MODULE_DESCRIPTION("Virtio pmem driver");
> > > +MODULE_LICENSE("GPL");
> > 
> > Only looked at this from the general virtio driver angle; seems fine
> > apart from some easy-to-fix issues and some personal style preference
> > things.
> 

Best regards,
Pankaj