Re: [PATCH v2 05/20] virtio: Implement get_shm_region for MMIO transport

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Aug 07, 2020 at 03:55:11PM -0400, Vivek Goyal wrote:
> From: Sebastien Boeuf <sebastien.boeuf@intel.com>
> 
> On MMIO a new set of registers is defined for finding SHM
> regions.  Add their definitions and use them to find the region.
> 
> Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
> Cc: kvm@vger.kernel.org
> Cc: "Michael S. Tsirkin" <mst@redhat.com>


Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/virtio/virtio_mmio.c     | 32 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_mmio.h | 11 +++++++++++
>  2 files changed, 43 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index 627ac0487494..2697c492cf78 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -498,6 +498,37 @@ static const char *vm_bus_name(struct virtio_device *vdev)
>  	return vm_dev->pdev->name;
>  }
>  
> +static bool vm_get_shm_region(struct virtio_device *vdev,
> +			      struct virtio_shm_region *region, u8 id)
> +{
> +	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> +	u64 len, addr;
> +
> +	/* Select the region we're interested in */
> +	writel(id, vm_dev->base + VIRTIO_MMIO_SHM_SEL);
> +
> +	/* Read the region size */
> +	len = (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_LEN_LOW);
> +	len |= (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_LEN_HIGH) << 32;
> +
> +	region->len = len;
> +
> +	/* Check if region length is -1. If that's the case, the shared memory
> +	 * region does not exist and there is no need to proceed further.
> +	 */
> +	if (len == ~(u64)0) {
> +		return false;
> +	}
> +

It might make sense to validate that addr/len do not overlap.
Will be useful for PCI too.
Can be a patch on top.

> +	/* Read the region base address */
> +	addr = (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_BASE_LOW);
> +	addr |= (u64) readl(vm_dev->base + VIRTIO_MMIO_SHM_BASE_HIGH) << 32;
> +
> +	region->addr = addr;
> +
> +	return true;
> +}
> +
>  static const struct virtio_config_ops virtio_mmio_config_ops = {
>  	.get		= vm_get,
>  	.set		= vm_set,
> @@ -510,6 +541,7 @@ static const struct virtio_config_ops virtio_mmio_config_ops = {
>  	.get_features	= vm_get_features,
>  	.finalize_features = vm_finalize_features,
>  	.bus_name	= vm_bus_name,
> +	.get_shm_region = vm_get_shm_region,
>  };
>  
>  
> diff --git a/include/uapi/linux/virtio_mmio.h b/include/uapi/linux/virtio_mmio.h
> index c4b09689ab64..0650f91bea6c 100644
> --- a/include/uapi/linux/virtio_mmio.h
> +++ b/include/uapi/linux/virtio_mmio.h
> @@ -122,6 +122,17 @@
>  #define VIRTIO_MMIO_QUEUE_USED_LOW	0x0a0
>  #define VIRTIO_MMIO_QUEUE_USED_HIGH	0x0a4
>  
> +/* Shared memory region id */
> +#define VIRTIO_MMIO_SHM_SEL             0x0ac
> +
> +/* Shared memory region length, 64 bits in two halves */
> +#define VIRTIO_MMIO_SHM_LEN_LOW         0x0b0
> +#define VIRTIO_MMIO_SHM_LEN_HIGH        0x0b4
> +
> +/* Shared memory region base address, 64 bits in two halves */
> +#define VIRTIO_MMIO_SHM_BASE_LOW        0x0b8
> +#define VIRTIO_MMIO_SHM_BASE_HIGH       0x0bc
> +
>  /* Configuration atomicity value */
>  #define VIRTIO_MMIO_CONFIG_GENERATION	0x0fc
>  
> -- 
> 2.25.4
>