Re: [RFC PATCH 3/6] vfio: Extend iommu-info to return MSIs automap state

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 2015-09-30 at 20:26 +0530, Bharat Bhushan wrote:
> This patch allows the user-space to know whether msi-pages
> are automatically mapped with some magic iova or not.
> 
> Even if the msi-pages are automatically mapped, still user-space
> wants to over-ride the automatic iova selection for msi-mapping.
> For this user-space need to know whether it is allowed to change
> the automatic mapping or not and this API provides this mechanism.
> Follow up patches will provide how to over-ride this.
> 
> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 32 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/vfio.h       |  3 +++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index fa5d3e4..3315fb6 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -59,6 +59,7 @@ struct vfio_iommu {
>  	struct rb_root		dma_list;
>  	bool			v2;
>  	bool			nesting;
> +	bool			allow_msi_reconfig;
>  	struct list_head	reserved_iova_list;
>  };
>  
> @@ -1117,6 +1118,23 @@ static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
>  	return ret;
>  }
>  
> +static
> +int vfio_domains_get_msi_maps(struct vfio_iommu *iommu,
> +			      struct iommu_domain_msi_maps *msi_maps)
> +{
> +	struct vfio_domain *d;
> +	int ret;
> +
> +	mutex_lock(&iommu->lock);
> +	/* All domains have same msi-automap property, pick first */
> +	d = list_first_entry(&iommu->domain_list, struct vfio_domain, next);
> +	ret = iommu_domain_get_attr(d->domain, DOMAIN_ATTR_MSI_MAPPING,
> +				    msi_maps);
> +	mutex_unlock(&iommu->lock);
> +
> +	return ret;
> +}
> +
>  static long vfio_iommu_type1_ioctl(void *iommu_data,
>  				   unsigned int cmd, unsigned long arg)
>  {
> @@ -1138,6 +1156,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  		}
>  	} else if (cmd == VFIO_IOMMU_GET_INFO) {
>  		struct vfio_iommu_type1_info info;
> +		struct iommu_domain_msi_maps msi_maps;
> +		int ret;
>  
>  		minsz = offsetofend(struct vfio_iommu_type1_info, iova_pgsizes);
>  
> @@ -1149,6 +1169,18 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  
>  		info.flags = 0;
>  
> +		ret = vfio_domains_get_msi_maps(iommu, &msi_maps);
> +		if (ret)
> +			return ret;

And now ioctl(VFIO_IOMMU_GET_INFO) no longer works for any IOMMU
implementing domain_get_attr but not supporting DOMAIN_ATTR_MSI_MAPPING.

> +
> +		if (msi_maps.override_automap) {
> +			info.flags |= VFIO_IOMMU_INFO_MSI_ALLOW_RECONFIG;
> +			iommu->allow_msi_reconfig = true;
> +		}
> +
> +		if (msi_maps.automap)
> +			info.flags |= VFIO_IOMMU_INFO_MSI_AUTOMAP;
> +
>  		info.iova_pgsizes = vfio_pgsize_bitmap(iommu);
>  
>  		return copy_to_user((void __user *)arg, &info, minsz);
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 1abd1a9..9998f6e 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -391,6 +391,9 @@ struct vfio_iommu_type1_info {
>  	__u32	argsz;
>  	__u32	flags;
>  #define VFIO_IOMMU_INFO_PGSIZES (1 << 0)	/* supported page sizes info */
> +#define VFIO_IOMMU_INFO_MSI_AUTOMAP (1 << 1)	/* MSI pages are auto-mapped
> +						   in iommu */
> +#define VFIO_IOMMU_INFO_MSI_ALLOW_RECONFIG (1 << 2) /* Allows reconfig automap*/
>  	__u64	iova_pgsizes;		/* Bitmap of supported page sizes */
>  };
>  

Once again, exposing interfaces to the user before they actually do
anything is backwards.