Re: [PATCH v12 2/7] virtio-pmem: Add virtio pmem driver

Cornelia Huck
2019-06-11T17:03:03Z

On Tue, 11 Jun 2019 22:07:57 +0530
Pankaj Gupta <pagupta@redhat.com> wrote:

> 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 <pagupta@redhat.com>
> Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Acked-by: Jakub Staron <jstaron@google.com>
> Tested-by: Jakub Staron <jstaron@google.com>
> ---
> drivers/nvdimm/Makefile | 1 +
> drivers/nvdimm/nd_virtio.c | 124 +++++++++++++++++++++++++++++++
> drivers/nvdimm/virtio_pmem.c | 122 ++++++++++++++++++++++++++++++
> drivers/nvdimm/virtio_pmem.h | 55 ++++++++++++++
> drivers/virtio/Kconfig | 11 +++
> include/uapi/linux/virtio_ids.h | 1 +
> include/uapi/linux/virtio_pmem.h | 35 +++++++++
> 7 files changed, 349 insertions(+)
> create mode 100644 drivers/nvdimm/nd_virtio.c
> create mode 100644 drivers/nvdimm/virtio_pmem.c
> create mode 100644 drivers/nvdimm/virtio_pmem.h
> create mode 100644 include/uapi/linux/virtio_pmem.h

Sorry about being late to the party; this one has been sitting in my
'to review' queue for far too long :(

(...)

> diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
> new file mode 100644
> index 000000000000..efc535723517
> --- /dev/null
> +++ b/drivers/nvdimm/nd_virtio.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 provides a virtio based flushing
> + * interface.
> + */
> +#include "virtio_pmem.h"
> +#include "nd.h"
> +
> + /* The interrupt handler */
> +void host_ack(struct virtqueue *vq)
> +{
> + struct virtio_pmem *vpmem = vq->vdev->priv;
> + struct virtio_pmem_request *req_data, *req_buf;
> + unsigned long flags;
> + unsigned int len;
> +
> + spin_lock_irqsave(&vpmem->pmem_lock, flags);
> + while ((req_data = virtqueue_get_buf(vq, &len)) != NULL) {
> + req_data->done = true;
> + wake_up(&req_data->host_acked);
> +
> + if (!list_empty(&vpmem->req_list)) {
> + req_buf = list_first_entry(&vpmem->req_list,
> + struct virtio_pmem_request, list);
> + req_buf->wq_buf_avail = true;
> + wake_up(&req_buf->wq_buf);
> + list_del(&req_buf->list);
> + }
> + }
> + spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> +}
> +EXPORT_SYMBOL_GPL(host_ack);

Nit: 'host_ack' looks a bit generic for an exported function... would
'virtio_pmem_host_ack' maybe be better?

> +
> + /* The request submission function */
> +int virtio_pmem_flush(struct nd_region *nd_region)

I don't see an EXPORT_SYMBOL_GPL() for this function... should it get
one, or should it be made static?

> +{
> + struct virtio_device *vdev = nd_region->provider_data;
> + struct virtio_pmem *vpmem = vdev->priv;
> + struct virtio_pmem_request *req_data;
> + struct scatterlist *sgs[2], sg, ret;
> + unsigned long flags;
> + int err, err1;
> +
> + might_sleep();
> + req_data = kmalloc(sizeof(*req_data), GFP_KERNEL);
> + if (!req_data)
> + return -ENOMEM;
> +
> + req_data->done = false;
> + init_waitqueue_head(&req_data->host_acked);
> + init_waitqueue_head(&req_data->wq_buf);
> + INIT_LIST_HEAD(&req_data->list);
> + req_data->req.type = cpu_to_virtio32(vdev, VIRTIO_PMEM_REQ_TYPE_FLUSH);
> + sg_init_one(&sg, &req_data->req, sizeof(req_data->req));
> + sgs[0] = &sg;
> + sg_init_one(&ret, &req_data->resp.ret, sizeof(req_data->resp));
> + sgs[1] = &ret;
> +
> + spin_lock_irqsave(&vpmem->pmem_lock, flags);
> + /*
> + * If virtqueue_add_sgs returns -ENOSPC then req_vq virtual
> + * queue does not have free descriptor. We add the request
> + * to req_list and wait for host_ack to wake us up when free
> + * slots are available.
> + */
> + while ((err = virtqueue_add_sgs(vpmem->req_vq, sgs, 1, 1, req_data,
> + GFP_ATOMIC)) == -ENOSPC) {
> +
> + dev_err(&vdev->dev, "failed to send command to virtio pmem device, no free slots in the virtqueue\n");

Hm... by the comment above I would have thought that this is not really
an error, but rather a temporary condition? Maybe downgrade this to
dev_info()?

> + req_data->wq_buf_avail = false;
> + list_add_tail(&req_data->list, &vpmem->req_list);
> + spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> +
> + /* A host response results in "host_ack" getting called */
> + wait_event(req_data->wq_buf, req_data->wq_buf_avail);
> + spin_lock_irqsave(&vpmem->pmem_lock, flags);
> + }
> + err1 = virtqueue_kick(vpmem->req_vq);
> + spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> + /*
> + * virtqueue_add_sgs failed with error different than -ENOSPC, we can't
> + * do anything about that.
> + */

Does it make sense to kick if you couldn't add at all?

> + if (err || !err1) {
> + dev_info(&vdev->dev, "failed to send command to virtio pmem device\n");

If this is dev_info, I think the error above really should be dev_info
as well (and maybe also log the error value)?

> + err = -EIO;
> + } else {
> + /* A host repsonse results in "host_ack" getting called */
> + wait_event(req_data->host_acked, req_data->done);
> + err = virtio32_to_cpu(vdev, req_data->resp.ret);
> + }
> +
> + kfree(req_data);
> + return err;
> +};
> +
> +/* The asynchronous flush callback function */
> +int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> +{
> + /* Create child bio for asynchronous flush and chain with
> + * parent bio. Otherwise directly call nd_region flush.
> + */

Nit: The comment should start with an otherwise empty /* line.

> + if (bio && bio->bi_iter.bi_sector != -1) {
> + struct bio *child = bio_alloc(GFP_ATOMIC, 0);
> +
> + if (!child)
> + return -ENOMEM;
> + bio_copy_dev(child, bio);
> + child->bi_opf = REQ_PREFLUSH;
> + child->bi_iter.bi_sector = -1;
> + bio_chain(child, bio);
> + submit_bio(child);
> + return 0;
> + }
> + if (virtio_pmem_flush(nd_region))
> + return -EIO;
> +
> + return 0;
> +};
> +EXPORT_SYMBOL_GPL(async_pmem_flush);
> +MODULE_LICENSE("GPL");

(...)

I have only some more minor comments; on the whole, this looks good to
me.