linux-kernel - Re: [PATCH] virtio_pmem: support feature SHMEM

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Date: Wed, 20 Dec 2023 11:57:42 +0800
From: Jason Wang <jasowang@...hat.com>
To: Changyuan Lyu <changyuanl@...gle.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>, "Michael S . Tsirkin" <mst@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Dan Williams <dan.j.williams@...el.com>, 
	Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, 
	virtualization@...ts.linux.dev, nvdimm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_pmem: support feature SHMEM_REGION

On Tue, Dec 19, 2023 at 3:19 PM Changyuan Lyu <changyuanl@...gle.com> wrote:
>
> As per virtio spec 1.2 section 5.19.5.2, if the feature
> VIRTIO_PMEM_F_SHMEM_REGION has been negotiated, the driver MUST query
> shared memory ID 0 for the physical address ranges.
>
> Signed-off-by: Changyuan Lyu <changyuanl@...gle.com>
> ---
>  drivers/nvdimm/virtio_pmem.c     | 29 +++++++++++++++++++++++++----
>  include/uapi/linux/virtio_pmem.h |  8 ++++++++
>  2 files changed, 33 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> index a92eb172f0e7..5b28d543728b 100644
> --- a/drivers/nvdimm/virtio_pmem.c
> +++ b/drivers/nvdimm/virtio_pmem.c
> @@ -35,6 +35,8 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
>         struct nd_region *nd_region;
>         struct virtio_pmem *vpmem;
>         struct resource res;
> +       struct virtio_shm_region shm_reg;
> +       bool have_shm;
>         int err = 0;
>
>         if (!vdev->config->get) {
> @@ -57,10 +59,23 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
>                 goto out_err;
>         }
>
> -       virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> -                       start, &vpmem->start);
> -       virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> -                       size, &vpmem->size);
> +       if (virtio_has_feature(vdev, VIRTIO_PMEM_F_SHMEM_REGION)) {
> +               have_shm = virtio_get_shm_region(vdev, &shm_reg,
> +                               (u8)VIRTIO_PMEM_SHMCAP_ID);
> +               if (!have_shm) {
> +                       dev_err(&vdev->dev, "failed to get shared memory region %d\n",
> +                                       VIRTIO_PMEM_SHMCAP_ID);
> +                       return -EINVAL;
> +               }
> +               vpmem->start = shm_reg.addr;
> +               vpmem->size = shm_reg.len;
> +       } else {
> +               virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> +                               start, &vpmem->start);
> +               virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> +                               size, &vpmem->size);
> +       }
> +
>
>         res.start = vpmem->start;
>         res.end   = vpmem->start + vpmem->size - 1;
> @@ -122,7 +137,13 @@ static void virtio_pmem_remove(struct virtio_device *vdev)
>         virtio_reset_device(vdev);
>  }
>
> +static unsigned int features[] = {
> +       VIRTIO_PMEM_F_SHMEM_REGION,
> +};
> +
>  static struct virtio_driver virtio_pmem_driver = {
> +       .feature_table          = features,
> +       .feature_table_size     = ARRAY_SIZE(features),
>         .driver.name            = KBUILD_MODNAME,
>         .driver.owner           = THIS_MODULE,
>         .id_table               = id_table,
> diff --git a/include/uapi/linux/virtio_pmem.h b/include/uapi/linux/virtio_pmem.h
> index d676b3620383..025174f6eacf 100644
> --- a/include/uapi/linux/virtio_pmem.h
> +++ b/include/uapi/linux/virtio_pmem.h
> @@ -14,6 +14,14 @@
>  #include <linux/virtio_ids.h>
>  #include <linux/virtio_config.h>
>
> +/* Feature bits */
> +#define VIRTIO_PMEM_F_SHMEM_REGION 0   /* guest physical address range will be
> +                                        * indicated as shared memory region 0
> +                                        */
> +
> +/* shmid of the shared memory region corresponding to the pmem */
> +#define VIRTIO_PMEM_SHMCAP_ID 0

NIT: not a native speaker, but any reason for "CAP" here? Would it be
better to use SHMMEM_REGION_ID?

Thanks

> +
>  struct virtio_pmem_config {
>         __le64 start;
>         __le64 size;
> --
> 2.43.0.472.g3155946c3a-goog
>