Re: [PATCH v7 2/6] virtio-pmem: Add virtio pmem driver

Dan Williams
2019-05-07T15:35:29Z

Hi Pankaj,

Some minor file placement comments below.

On Thu, Apr 25, 2019 at 10:02 PM 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>
> ---
> drivers/nvdimm/virtio_pmem.c | 114 +++++++++++++++++++++++++++++
> drivers/virtio/Kconfig | 10 +++
> drivers/virtio/Makefile | 1 +
> drivers/virtio/pmem.c | 118 +++++++++++++++++++++++++++++++
> include/linux/virtio_pmem.h | 60 ++++++++++++++++
> include/uapi/linux/virtio_ids.h | 1 +
> include/uapi/linux/virtio_pmem.h | 10 +++
> 7 files changed, 314 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/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> new file mode 100644
> index 000000000000..66b582f751a3
> --- /dev/null
> +++ b/drivers/nvdimm/virtio_pmem.c
> @@ -0,0 +1,114 @@
> +// 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 <linux/virtio_pmem.h>
> +#include "nd.h"
> +
> + /* The interrupt handler */
> +void host_ack(struct virtqueue *vq)
> +{
> + unsigned int len;
> + unsigned long flags;
> + struct virtio_pmem_request *req, *req_buf;
> + struct virtio_pmem *vpmem = vq->vdev->priv;
> +
> + spin_lock_irqsave(&vpmem->pmem_lock, flags);
> + while ((req = virtqueue_get_buf(vq, &len)) != NULL) {
> + req->done = true;
> + wake_up(&req->host_acked);
> +
> + if (!list_empty(&vpmem->req_list)) {
> + req_buf = list_first_entry(&vpmem->req_list,
> + struct virtio_pmem_request, list);
> + list_del(&vpmem->req_list);
> + req_buf->wq_buf_avail = true;
> + wake_up(&req_buf->wq_buf);
> + }
> + }
> + spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> +}
> +EXPORT_SYMBOL_GPL(host_ack);
> +
> + /* The request submission function */
> +int virtio_pmem_flush(struct nd_region *nd_region)
> +{
> + int err;
> + unsigned long flags;
> + struct scatterlist *sgs[2], sg, ret;
> + struct virtio_device *vdev = nd_region->provider_data;
> + struct virtio_pmem *vpmem = vdev->priv;
> + struct virtio_pmem_request *req;
> +
> + might_sleep();
> + req = kmalloc(sizeof(*req), GFP_KERNEL);
> + if (!req)
> + return -ENOMEM;
> +
> + req->done = req->wq_buf_avail = false;
> + strcpy(req->name, "FLUSH");
> + init_waitqueue_head(&req->host_acked);
> + init_waitqueue_head(&req->wq_buf);
> + sg_init_one(&sg, req->name, strlen(req->name));
> + sgs[0] = &sg;
> + sg_init_one(&ret, &req->ret, sizeof(req->ret));
> + sgs[1] = &ret;
> +
> + spin_lock_irqsave(&vpmem->pmem_lock, flags);
> + err = virtqueue_add_sgs(vpmem->req_vq, sgs, 1, 1, req, GFP_ATOMIC);
> + if (err) {
> + dev_err(&vdev->dev, "failed to send command to virtio pmem device\n");
> +
> + list_add_tail(&vpmem->req_list, &req->list);
> + spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> +
> + /* When host has read buffer, this completes via host_ack */
> + wait_event(req->wq_buf, req->wq_buf_avail);
> + spin_lock_irqsave(&vpmem->pmem_lock, flags);
> + }
> + err = virtqueue_kick(vpmem->req_vq);
> + spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
> +
> + if (!err) {
> + err = -EIO;
> + goto ret;
> + }
> + /* When host has read buffer, this completes via host_ack */
> + wait_event(req->host_acked, req->done);
> + err = req->ret;
> +ret:
> + kfree(req);
> + return err;
> +};
> +
> + /* The asynchronous flush callback function */
> +int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> +{
> + int rc = 0;
> +
> + /* Create child bio for asynchronous flush and chain with
> + * parent bio. Otherwise directly call nd_region flush.
> + */
> + 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);
> + } else {
> + if (virtio_pmem_flush(nd_region))
> + rc = -EIO;
> + }
> +
> + return rc;
> +};
> +EXPORT_SYMBOL_GPL(async_pmem_flush);
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 35897649c24f..9f634a2ed638 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -42,6 +42,16 @@ config VIRTIO_PCI_LEGACY
>
> If unsure, say Y.
>
> +config VIRTIO_PMEM
> + tristate "Support for virtio pmem driver"
> + depends on VIRTIO
> + depends on LIBNVDIMM
> + help
> + This driver provides support for virtio based flushing interface
> + for persistent memory range.
> +
> + If unsure, say M.
> +
> config VIRTIO_BALLOON
> tristate "Virtio balloon driver"
> depends on VIRTIO
> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> index 3a2b5c5dcf46..143ce91eabe9 100644
> --- a/drivers/virtio/Makefile
> +++ b/drivers/virtio/Makefile
> @@ -6,3 +6,4 @@ virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
> virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
> obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
> obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
> +obj-$(CONFIG_VIRTIO_PMEM) += pmem.o ../nvdimm/virtio_pmem.o
> diff --git a/drivers/virtio/pmem.c b/drivers/virtio/pmem.c
> new file mode 100644
> index 000000000000..309788628e41
> --- /dev/null
> +++ b/drivers/virtio/pmem.c

It's not clear to me why this driver is located in drivers/virtio/

> @@ -0,0 +1,118 @@
> +// 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>

...especially because it seems to require nvdimm internals.

However I don't see why that header is included.

In any event lets move this to drivers/nvdimm/virtio.c to live
alongside the other generic bus provider drivers/nvdimm/e820.c.

> +
> +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)
> +{
> + /* single vq */
> + vpmem->req_vq = virtio_find_single_vq(vpmem->vdev,
> + host_ack, "flush_queue");
> + if (IS_ERR(vpmem->req_vq))
> + return PTR_ERR(vpmem->req_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 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 access disabled\n",
> + __func__);
> + return -EINVAL;
> + }
> +
> + vpmem = devm_kzalloc(&vdev->dev, sizeof(*vpmem), GFP_KERNEL);
> + if (!vpmem) {
> + err = -ENOMEM;
> + goto out_err;
> + }
> +
> + vpmem->vdev = vdev;
> + vdev->priv = vpmem;
> + 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_register(&vdev->dev,
> + &vpmem->nd_desc);
> + if (!vpmem->nvdimm_bus)
> + goto out_vq;
> +
> + dev_set_drvdata(&vdev->dev, vpmem->nvdimm_bus);
> +
> + ndr_desc.res = &res;
> + ndr_desc.numa_node = nid;
> + ndr_desc.flush = async_pmem_flush;
> + set_bit(ND_REGION_PAGEMAP, &ndr_desc.flags);
> + set_bit(ND_REGION_ASYNC, &ndr_desc.flags);
> + nd_region = nvdimm_pmem_region_create(vpmem->nvdimm_bus, &ndr_desc);
> +
> + if (!nd_region)
> + goto out_nd;
> + nd_region->provider_data = dev_to_virtio
> + (nd_region->dev.parent->parent);
> + return 0;
> +out_nd:
> + err = -ENXIO;
> + nvdimm_bus_unregister(vpmem->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 nvdimm_bus *nvdimm_bus = dev_get_drvdata(&vdev->dev);
> +
> + nvdimm_bus_unregister(nvdimm_bus);
> + vdev->config->del_vqs(vdev);
> + vdev->config->reset(vdev);
> +}
> +
> +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");
> diff --git a/include/linux/virtio_pmem.h b/include/linux/virtio_pmem.h
> new file mode 100644
> index 000000000000..ab1da877575d
> --- /dev/null
> +++ b/include/linux/virtio_pmem.h

Why is this a global header?

Seems it can move to drivers/nvdimm/virtio.h.

Also, I'd like to get a virtio ack from Michael (mst@redhat.com)
before taking this through the nvdimm tree.

> @@ -0,0 +1,60 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * virtio_pmem.h: virtio pmem Driver
> + *
> + * Discovers persistent memory range information
> + * from host and provides a virtio based flushing
> + * interface.
> + **/
> +
> +#ifndef _LINUX_VIRTIO_PMEM_H
> +#define _LINUX_VIRTIO_PMEM_H
> +
> +#include <linux/virtio_ids.h>
> +#include <linux/module.h>
> +#include <linux/virtio_config.h>
> +#include <uapi/linux/virtio_pmem.h>
> +#include <linux/libnvdimm.h>
> +#include <linux/spinlock.h>
> +
> +struct virtio_pmem_request {
> + /* Host return status corresponding to flush request */
> + int ret;
> +
> + /* command name*/
> + char name[16];
> +
> + /* Wait queue to process deferred work after ack from host */
> + wait_queue_head_t host_acked;
> + bool done;
> +
> + /* Wait queue to process deferred work after virt queue buffer avail */
> + wait_queue_head_t wq_buf;
> + bool wq_buf_avail;
> + struct list_head list;
> +};
> +
> +struct virtio_pmem {
> + struct virtio_device *vdev;
> +
> + /* Virtio pmem request queue */
> + struct virtqueue *req_vq;
> +
> + /* nvdimm bus registers virtio pmem device */
> + struct nvdimm_bus *nvdimm_bus;
> + struct nvdimm_bus_descriptor nd_desc;
> +
> + /* List to store deferred work if virtqueue is full */
> + struct list_head req_list;
> +
> + /* Synchronize virtqueue data */
> + spinlock_t pmem_lock;
> +
> + /* Memory region information */
> + uint64_t start;
> + uint64_t size;
> +};
> +
> +void host_ack(struct virtqueue *vq);
> +int async_pmem_flush(struct nd_region *nd_region, struct bio *bio);
> +#endif
> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index 6d5c3b2d4f4d..32b2f94d1f58 100644
> --- a/include/uapi/linux/virtio_ids.h
> +++ b/include/uapi/linux/virtio_ids.h
> @@ -43,5 +43,6 @@
> #define VIRTIO_ID_INPUT 18 /* virtio input */
> #define VIRTIO_ID_VSOCK 19 /* virtio vsock transport */
> #define VIRTIO_ID_CRYPTO 20 /* virtio crypto */
> +#define VIRTIO_ID_PMEM 27 /* virtio pmem */
>
> #endif /* _LINUX_VIRTIO_IDS_H */
> diff --git a/include/uapi/linux/virtio_pmem.h b/include/uapi/linux/virtio_pmem.h
> new file mode 100644
> index 000000000000..fa3f7d52717a
> --- /dev/null
> +++ b/include/uapi/linux/virtio_pmem.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _UAPI_LINUX_VIRTIO_PMEM_H
> +#define _UAPI_LINUX_VIRTIO_PMEM_H
> +
> +struct virtio_pmem_config {
> + __le64 start;
> + __le64 size;
> +};
> +#endif
> --
> 2.20.1
>