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SubjectRe: [Qemu-devel] [RFC v2 1/2] virtio: add pmem driver
On Wed, Apr 25, 2018 at 04:54:13PM +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 <pagupta@redhat.com>
> ---
> drivers/virtio/Kconfig | 12 ++++
> drivers/virtio/Makefile | 1 +
> drivers/virtio/virtio_pmem.c | 118 +++++++++++++++++++++++++++++++++++++++
> include/linux/libnvdimm.h | 4 ++
> include/uapi/linux/virtio_ids.h | 1 +
> include/uapi/linux/virtio_pmem.h | 58 +++++++++++++++++++
> 6 files changed, 194 insertions(+)
> create mode 100644 drivers/virtio/virtio_pmem.c
> create mode 100644 include/uapi/linux/virtio_pmem.h
>
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 3589764..879335d 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -42,6 +42,18 @@ config VIRTIO_PCI_LEGACY
>
> If unsure, say Y.
>
> +config VIRTIO_PMEM
> + tristate "Virtio pmem driver"
> + depends on VIRTIO
> + help
> + This driver adds persistent memory range to nd_region and registers
> + with nvdimm bus. NVDIMM 'pmem' driver later allocates a persistent
> + memory range on the memory information added by this driver. In addition
> + to this, 'virtio-pmem' driver also provides a paravirt flushing interface
> + from guest to host.
> +
> + 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 3a2b5c5..cbe91c6 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) += virtio_pmem.o
> diff --git a/drivers/virtio/virtio_pmem.c b/drivers/virtio/virtio_pmem.c
> new file mode 100644
> index 0000000..0906d2d
> --- /dev/null
> +++ b/drivers/virtio/virtio_pmem.c
> @@ -0,0 +1,118 @@

SPDX license line? See Documentation/process/license-rules.rst.

> +/* Virtio pmem Driver
> + *
> + * Discovers persitent memory range information

s/persitent/persistent/

> + * from host and provides a virtio based flushing
> + * interface.
> + */
> +
> +#include <linux/virtio.h>
> +#include <linux/swap.h>
> +#include <linux/workqueue.h>
> +#include <linux/delay.h>
> +#include <linux/slab.h>
> +#include <linux/module.h>
> +#include <linux/oom.h>
> +#include <linux/wait.h>
> +#include <linux/magic.h>
> +#include <linux/virtio_pmem.h>
> +#include <linux/libnvdimm.h>

Are all these headers really needed? delay.h? oom.h?

> +
> +static int init_vq(struct virtio_pmem *vpmem)
> +{
> + struct virtqueue *vq;
> +
> + /* single vq */
> + vpmem->req_vq = vq = virtio_find_single_vq(vpmem->vdev,
> + NULL, "flush_queue");
> +
> + if (IS_ERR(vq))
> + return PTR_ERR(vq);
> +
> + 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);
> + static struct nvdimm_bus_descriptor nd_desc;
> +
> + if (!vdev->config->get) {
> + dev_err(&vdev->dev, "%s failure: config disabled\n",
> + __func__);
> + return -EINVAL;
> + }
> +
> + vdev->priv = vpmem = devm_kzalloc(&vdev->dev, sizeof(*vpmem),
> + GFP_KERNEL);
> + if (!vpmem) {
> + err = -ENOMEM;
> + goto out;
> + }
> +
> + vpmem->vdev = vdev;
> + err = init_vq(vpmem);
> + if (err)
> + goto out;
> +
> + 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;
> +
> + memset(&nd_desc, 0, sizeof(nd_desc));
> + nd_desc.provider_name = "virtio-pmem";
> + nd_desc.module = THIS_MODULE;
> + nvdimm_bus = nvdimm_bus_register(&vdev->dev, &nd_desc);
> +
> + if (!nvdimm_bus)
> + goto out_nd;
> + dev_set_drvdata(&vdev->dev, nvdimm_bus);
> +
> + memset(&ndr_desc, 0, sizeof(ndr_desc));
> + ndr_desc.res = &res;
> + ndr_desc.numa_node = nid;
> + set_bit(ND_REGION_PAGEMAP, &ndr_desc.flags);
> + set_bit(ND_REGION_VIRTIO, &ndr_desc.flags);
> +
> + if (!nvdimm_pmem_region_create(nvdimm_bus, &ndr_desc))
> + goto out_nd;
> +
> + virtio_device_ready(vdev);
> + return 0;
> +
> +out_nd:
> + nvdimm_bus_unregister(nvdimm_bus);
> +out:
> + dev_err(&vdev->dev, "failed to register virtio pmem memory\n");
> + vdev->config->del_vqs(vdev);
> + 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);
> +}
> +
> +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/libnvdimm.h b/include/linux/libnvdimm.h
> index 097072c..b1b7f14 100644
> --- a/include/linux/libnvdimm.h
> +++ b/include/linux/libnvdimm.h
> @@ -58,6 +58,10 @@ enum {
> * (ADR)
> */
> ND_REGION_PERSIST_MEMCTRL = 2,
> + /*
> + * region flag indicating to use VIRTIO flush interface for pmem
> + */
> + ND_REGION_VIRTIO = 3,

Can you add a generic flush callback to libnvdimm instead? That way
virtio and other drivers can hook in without hardcoding knowledge of
these drivers into libnvdimm.

>
> /* mark newly adjusted resources as requiring a label update */
> DPA_RESOURCE_ADJUSTED = 1 << 0,
> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index 6d5c3b2..5ebd049 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 21 /* 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 0000000..2ec27cb
> --- /dev/null
> +++ b/include/uapi/linux/virtio_pmem.h
> @@ -0,0 +1,58 @@
> +/* Virtio pmem Driver
> + *
> + * Discovers persitent memory range information

s/persitent/persistent/

> + * from host and provides a virtio based flushing
> + * interface.
> + */
> +
> +#ifndef _LINUX_VIRTIO_PMEM_H
> +#define _LINUX_VIRTIO_PMEM_H
> +
> +#include <linux/types.h>
> +#include <linux/virtio_types.h>
> +#include <linux/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +#include <linux/virtio_ring.h>
> +
> +
> +struct virtio_pmem_config {
> +
> + uint64_t start;
> + uint64_t size;
> +};
> +
> +struct virtio_pmem {
> +
> + struct virtio_device *vdev;
> + struct virtqueue *req_vq;
> +
> + uint64_t start;
> + uint64_t size;
> +} __packed;

This is a userspace API header file, it should contain definitions that
userspace programs need. struct virtio_pmem is a kernel-internal struct
that should not be in the uapi headers.

Only define virtio spec structs in this header file (e.g. config space,
request structs, etc).

> +static struct virtio_device_id id_table[] = {
> + { VIRTIO_ID_PMEM, VIRTIO_DEV_ANY_ID },
> + { 0 },
> +};

Why is static variable in the header file?

> +
> +void virtio_pmem_flush(struct device *dev)

This only implements flush command submission, not completion. Maybe
the next patch will implement that but it's a little strange to only see
half of the flush operation.

Please put the whole flush operation in one patch so it can be reviewed
easily. At this point I don't know if you've forgotten to implement
wait for completion.

> +{

Why is this function body in the header file?

> + struct scatterlist sg;
> + struct virtio_device *vdev = dev_to_virtio(dev->parent->parent);
> + struct virtio_pmem *vpmem = vdev->priv;
> + char *buf = "FLUSH";

I'm surprised this compiles without a warning. String literals should
be constant but the char pointer isn't constant.

> + int err;
> +
> + sg_init_one(&sg, buf, sizeof(buf));
> +
> + err = virtqueue_add_outbuf(vpmem->req_vq, &sg, 1, buf, GFP_KERNEL);
> +
> + if (err) {
> + dev_err(&vdev->dev, "failed to send command to virtio pmem device\n");
> + return;
> + }
> +
> + virtqueue_kick(vpmem->req_vq);

Is any locking necessary? Two CPUs must not invoke virtio_pmem_flush()
at the same time. Not sure if anything guarantees this, maybe you're
relying on libnvdimm but I haven't checked.

> +};
> +
> +#endif
> --
> 2.9.3
>
>
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