Re: [Qemu-devel] [PATCH v8 2/6] virtio-pmem: Add virtio pmem driver

[Michael S. Tsirkin]

On Fri, May 10, 2019 at 09:21:58PM +0530, Pankaj Gupta 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 <address@hidden>
> Reviewed-by: Yuval Shaia <address@hidden>

Acked-by: Michael S. Tsirkin <address@hidden>

> ---
>  drivers/nvdimm/Makefile          |   1 +
>  drivers/nvdimm/nd_virtio.c       | 129 +++++++++++++++++++++++++++++++
>  drivers/nvdimm/virtio_pmem.c     | 117 ++++++++++++++++++++++++++++
>  drivers/virtio/Kconfig           |  10 +++
>  include/linux/virtio_pmem.h      |  60 ++++++++++++++
>  include/uapi/linux/virtio_ids.h  |   1 +
>  include/uapi/linux/virtio_pmem.h |  10 +++
>  7 files changed, 328 insertions(+)
>  create mode 100644 drivers/nvdimm/nd_virtio.c
>  create mode 100644 drivers/nvdimm/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/Makefile b/drivers/nvdimm/Makefile
> index 6f2a088afad6..cefe233e0b52 100644
> --- a/drivers/nvdimm/Makefile
> +++ b/drivers/nvdimm/Makefile
> @@ -5,6 +5,7 @@ obj-$(CONFIG_ND_BTT) += nd_btt.o
>  obj-$(CONFIG_ND_BLK) += nd_blk.o
>  obj-$(CONFIG_X86_PMEM_LEGACY) += nd_e820.o
>  obj-$(CONFIG_OF_PMEM) += of_pmem.o
> +obj-$(CONFIG_VIRTIO_PMEM) += virtio_pmem.o nd_virtio.o
>  
>  nd_pmem-y := pmem.o
>  
> diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
> new file mode 100644
> index 000000000000..ed7ddcc5a62c
> --- /dev/null
> +++ b/drivers/nvdimm/nd_virtio.c
> @@ -0,0 +1,129 @@
> +// 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);
> +                     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);
> +
> + /* The request submission function */
> +int virtio_pmem_flush(struct nd_region *nd_region)
> +{
> +     int err, err1;
> +     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 = false;
> +     strcpy(req->name, "FLUSH");
> +     init_waitqueue_head(&req->host_acked);
> +     init_waitqueue_head(&req->wq_buf);
> +     INIT_LIST_HEAD(&req->list);
> +     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);
> +      /*
> +       * 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,
> +                                     GFP_ATOMIC)) == -ENOSPC) {
> +
> +             dev_err(&vdev->dev, "failed to send command to virtio pmem"\
> +                     "device, no free slots in the virtqueue\n");
> +             req->wq_buf_avail = false;
> +             list_add_tail(&req->list, &vpmem->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);
> +     }
> +     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.
> +      */
> +     if (err || !err1) {
> +             dev_info(&vdev->dev, "failed to send command to virtio pmem 
> device\n");
> +             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/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> new file mode 100644
> index 000000000000..cfc6381c4e5d
> --- /dev/null
> +++ b/drivers/nvdimm/virtio_pmem.c
> @@ -0,0 +1,117 @@
> +// 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 "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)
> +{
> +     /* 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/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/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
> @@ -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