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Date: Wed, 20 Dec 2023 02:44:45 -0500
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Changyuan Lyu <changyuanl@google.com>
Cc: dan.j.williams@intel.com, dave.jiang@intel.com, jasowang@redhat.com,
	linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev,
	pankaj.gupta.linux@gmail.com, virtualization@lists.linux.dev,
	vishal.l.verma@intel.com, xuanzhuo@linux.alibaba.com
Subject: Re: [PATCH v3] virtio_pmem: support feature SHMEM_REGION
Message-ID: <20231220023653-mutt-send-email-mst@kernel.org>
References: <20231220020100-mutt-send-email-mst@kernel.org>
 <20231220073227.252605-1-changyuanl@google.com>
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In-Reply-To: <20231220073227.252605-1-changyuanl@google.com>

On Tue, Dec 19, 2023 at 11:32:27PM -0800, Changyuan Lyu wrote:
> On Tue, Dec 19, 2023 at 11:01 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> > 
> > This is not a great description. Please describe what the patch does.
> 
> Thanks for the feedback! Please see the v3 patch below.
> 
> ---8<---
> 
> This patch adds the support for feature VIRTIO_PMEM_F_SHMEM_REGION
> (virtio spec v1.2 section 5.19.5.2 [1]). Feature bit
> VIRTIO_PMEM_F_SHMEM_REGION is added to the driver feature
> table.
> 
> If the driver feature bit VIRTIO_PMEM_F_SHMEM_REGION is found,
> during probe, virtio pmem ignores the `start` and `size` fields in
> device config and looks for a shared memory region of id 0. The
> physical address range of the pmem is then determined by 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@google.com>
> 
> ---
> 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     | 30 ++++++++++++++++++++++++++----
>  include/uapi/linux/virtio_pmem.h |  8 ++++++++
>  2 files changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> index a92eb172f0e7..8e447c7558cb 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 +59,24 @@ 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_SHMEM_REGION_ID);
> +		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.


> +		}
> +		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 +138,13 @@ 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..c5e49b6e58b1 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
> +					 */


Either make this comment shorter to fit in one line, or put the
multi-line comment before the define.

> +
> +/* 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