Re: [PATCH v4] virtio_pmem: support feature SHMEM_REGION

[Jason Wang]

On Thu, Dec 21, 2023 at 4:49 AM Changyuan Lyu <changyuanl@xxxxxxxxxx> wrote:
>
> Thanks Michael for the feedback!
>
> On Tue, Dec 19, 2023 at 11:44 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> >
> > > On Tue, Dec 19, 2023 at 11:32:27PM -0800, Changyuan Lyu wrote:
> > >
> > > +           if (!have_shm) {
> > > +                   dev_err(&vdev->dev, "failed to get shared memory region %d\n",
> > > +                                   VIRTIO_PMEM_SHMEM_REGION_ID);
> > > +                   err = -ENXIO;
> > > +                   goto out_vq;
> > > +           }
> >
> > Maybe additionally, add a validate callback and clear
> > VIRTIO_PMEM_F_SHMEM_REGION if VIRTIO_PMEM_SHMEM_REGION_ID is not there.
>
> Done.
>
> > > +/* Feature bits */
> > > +#define VIRTIO_PMEM_F_SHMEM_REGION 0       /* guest physical address range will be
> > > +                                    * indicated as shared memory region 0
> > > +                                    */
> >
> > Either make this comment shorter to fit in one line, or put the
> > multi-line comment before the define.
>
> Done.
>
> ---8<---
>
> This patch adds the support for feature VIRTIO_PMEM_F_SHMEM_REGION
> (virtio spec v1.2 section 5.19.5.2 [1]).
>
> During feature negotiation, if VIRTIO_PMEM_F_SHMEM_REGION is offered
> by the device, the driver looks for a shared memory region of id 0.
> If it is found, this feature is understood. Otherwise, this feature
> bit is cleared.
>
> During probe, if VIRTIO_PMEM_F_SHMEM_REGION has been negotiated,
> virtio pmem ignores the `start` and `size` fields in device config
> and uses the physical address range of shared memory region 0.
>
> [1] https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html#x1-6480002
>
> Signed-off-by: Changyuan Lyu <changyuanl@xxxxxxxxxx>

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

Thanks

> ---
> v4:
>   * added virtio_pmem_validate callback.
> v3:
>   * updated the patch description.
> V2:
>   * renamed VIRTIO_PMEM_SHMCAP_ID to VIRTIO_PMEM_SHMEM_REGION_ID
>   * fixed the error handling when region 0 does not exist
> ---
>  drivers/nvdimm/virtio_pmem.c     | 36 ++++++++++++++++++++++++++++----
>  include/uapi/linux/virtio_pmem.h |  7 +++++++
>  2 files changed, 39 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> index a92eb172f0e7..4ceced5cefcf 100644
> --- a/drivers/nvdimm/virtio_pmem.c
> +++ b/drivers/nvdimm/virtio_pmem.c
> @@ -29,12 +29,27 @@ static int init_vq(struct virtio_pmem *vpmem)
>         return 0;
>  };
>
> +static int virtio_pmem_validate(struct virtio_device *vdev)
> +{
> +       struct virtio_shm_region shm_reg;
> +
> +       if (virtio_has_feature(vdev, VIRTIO_PMEM_F_SHMEM_REGION) &&
> +               !virtio_get_shm_region(vdev, &shm_reg, (u8)VIRTIO_PMEM_SHMEM_REGION_ID)
> +       ) {
> +               dev_notice(&vdev->dev, "failed to get shared memory region %d\n",
> +                               VIRTIO_PMEM_SHMEM_REGION_ID);
> +               __virtio_clear_bit(vdev, VIRTIO_PMEM_F_SHMEM_REGION);
> +       }
> +       return 0;
> +}
> +
>  static int virtio_pmem_probe(struct virtio_device *vdev)
>  {
>         struct nd_region_desc ndr_desc = {};
>         struct nd_region *nd_region;
>         struct virtio_pmem *vpmem;
>         struct resource res;
> +       struct virtio_shm_region shm_reg;
>         int err = 0;
>
>         if (!vdev->config->get) {
> @@ -57,10 +72,16 @@ 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)) {
> +               virtio_get_shm_region(vdev, &shm_reg, (u8)VIRTIO_PMEM_SHMEM_REGION_ID);
> +               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;
> @@ -122,10 +143,17 @@ 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,
> +       .validate               = virtio_pmem_validate,
>         .probe                  = virtio_pmem_probe,
>         .remove                 = virtio_pmem_remove,
>  };
> diff --git a/include/uapi/linux/virtio_pmem.h b/include/uapi/linux/virtio_pmem.h
> index d676b3620383..ede4f3564977 100644
> --- a/include/uapi/linux/virtio_pmem.h
> +++ b/include/uapi/linux/virtio_pmem.h
> @@ -14,6 +14,13 @@
>  #include <linux/virtio_ids.h>
>  #include <linux/virtio_config.h>
>
> +/* Feature bits */
> +/* guest physical address range will be indicated as shared memory region 0 */
> +#define VIRTIO_PMEM_F_SHMEM_REGION 0
> +
> +/* shmid of the shared memory region corresponding to the pmem */
> +#define VIRTIO_PMEM_SHMEM_REGION_ID 0
> +
>  struct virtio_pmem_config {
>         __le64 start;
>         __le64 size;
> --
> 2.43.0.472.g3155946c3a-goog
>