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Date:   Wed, 8 May 2019 07:19:11 -0400 (EDT)
From:   Pankaj Gupta <pagupta@redhat.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     cohuck@redhat.com, Jan Kara <jack@suse.cz>,
        KVM list <kvm@vger.kernel.org>,
        Jason Wang <jasowang@redhat.com>, david <david@fromorbit.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Qemu Developers <qemu-devel@nongnu.org>,
        virtualization@lists.linux-foundation.org,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Ross Zwisler <zwisler@kernel.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Dave Jiang <dave.jiang@intel.com>,
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        Vishal L Verma <vishal.l.verma@intel.com>,
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Subject: Re: [Qemu-devel] [PATCH v7 2/6] virtio-pmem: Add virtio pmem driver
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Thread-Topic: virtio-pmem: Add virtio pmem driver
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Hi Dan,

Thank you for the review. Please see my reply inline.

> 
> Hi Pankaj,
> 
> Some minor file placement comments below.

Sure.

> 
> 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/

Like other VIRTIO drivers, I placed it initially in drivers/virtio directory.

> 
> > @@ -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.

Removed.

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

o.k. Makes sense.

> 
> > +
> > +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?

This is where other virtio driver headers are also placed.
I think this is to access uapi config file in :

./include/uapi/linux/virtio_pmem.h

Is it okay if we keep 'virtio_pmem.h' in 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.

Sure, Will post v8 with the suggestions.

Thanks,
Pankaj

> 
> > @@ -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
> >
> 
>