Re: [PATCH v9 4/7] vfio: allow reserved msi iova registration

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

On Wed,  4 May 2016 11:54:15 +0000
Eric Auger <eric.auger@linaro.org> wrote:

> The user is allowed to register a reserved MSI IOVA range by using the
> DMA MAP API and setting the new flag: VFIO_DMA_MAP_FLAG_MSI_RESERVED_IOVA.
> This region is stored in the vfio_dma rb tree. At that point the iova
> range is not mapped to any target address yet. The host kernel will use
> those iova when needed, typically when MSIs are allocated.
> 
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
> 
> ---
> v7 -> v8:
> - use iommu_msi_set_aperture function. There is no notion of
>   unregistration anymore since the reserved msi slot remains
>   until the container gets closed.
> 
> v6 -> v7:
> - use iommu_free_reserved_iova_domain
> - convey prot attributes downto dma-reserved-iommu iova domain creation
> - reserved bindings teardown now performed on iommu domain destruction
> - rename VFIO_DMA_MAP_FLAG_MSI_RESERVED_IOVA into
>          VFIO_DMA_MAP_FLAG_RESERVED_MSI_IOVA
> - change title
> - pass the protection attribute to dma-reserved-iommu API
> 
> v3 -> v4:
> - use iommu_alloc/free_reserved_iova_domain exported by dma-reserved-iommu
> - protect vfio_register_reserved_iova_range implementation with
>   CONFIG_IOMMU_DMA_RESERVED
> - handle unregistration by user-space and on vfio_iommu_type1 release
> 
> v1 -> v2:
> - set returned value according to alloc_reserved_iova_domain result
> - free the iova domains in case any error occurs
> 
> RFC v1 -> v1:
> - takes into account Alex comments, based on
>   [RFC PATCH 1/6] vfio: Add interface for add/del reserved iova region:
> - use the existing dma map/unmap ioctl interface with a flag to register
>   a reserved IOVA range. A single reserved iova region is allowed.
> ---
>  drivers/vfio/vfio_iommu_type1.c | 78 ++++++++++++++++++++++++++++++++++++++++-
>  include/uapi/linux/vfio.h       | 10 +++++-
>  2 files changed, 86 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 94a9916..4d3a6f1 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -36,6 +36,7 @@
>  #include <linux/uaccess.h>
>  #include <linux/vfio.h>
>  #include <linux/workqueue.h>
> +#include <linux/msi-iommu.h>
>  
>  #define DRIVER_VERSION  "0.2"
>  #define DRIVER_AUTHOR   "Alex Williamson <alex.williamson@redhat.com>"
> @@ -445,6 +446,20 @@ static void vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma)
>  	vfio_lock_acct(-unlocked);
>  }
>  
> +static int vfio_set_msi_aperture(struct vfio_iommu *iommu,
> +				dma_addr_t iova, size_t size)
> +{
> +	struct vfio_domain *d;
> +	int ret = 0;
> +
> +	list_for_each_entry(d, &iommu->domain_list, next) {
> +		ret = iommu_msi_set_aperture(d->domain, iova, iova + size - 1);
> +		if (ret)
> +			break;
> +	}
> +	return ret;
> +}
> +
>  static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
>  {
>  	vfio_unmap_unpin(iommu, dma);
> @@ -693,6 +708,63 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>  	return ret;
>  }
>  
> +static int vfio_register_msi_range(struct vfio_iommu *iommu,
> +				   struct vfio_iommu_type1_dma_map *map)
> +{
> +	dma_addr_t iova = map->iova;
> +	size_t size = map->size;
> +	int ret = 0;
> +	struct vfio_dma *dma;
> +	unsigned long order;
> +	uint64_t mask;
> +
> +	/* Verify that none of our __u64 fields overflow */
> +	if (map->size != size || map->iova != iova)
> +		return -EINVAL;
> +
> +	order =  __ffs(vfio_pgsize_bitmap(iommu));
> +	mask = ((uint64_t)1 << order) - 1;
> +
> +	WARN_ON(mask & PAGE_MASK);
> +
> +	if (!size || (size | iova) & mask)
> +		return -EINVAL;
> +
> +	/* Don't allow IOVA address wrap */
> +	if (iova + size - 1 < iova)
> +		return -EINVAL;
> +
> +	mutex_lock(&iommu->lock);
> +
> +	if (vfio_find_dma(iommu, iova, size, VFIO_IOVA_ANY)) {
> +		ret =  -EEXIST;
> +		goto unlock;
> +	}
> +
> +	dma = kzalloc(sizeof(*dma), GFP_KERNEL);
> +	if (!dma) {
> +		ret = -ENOMEM;
> +		goto unlock;
> +	}
> +
> +	dma->iova = iova;
> +	dma->size = size;
> +	dma->type = VFIO_IOVA_RESERVED;

[oops, forgot to send this reply with the others]

I'm tempted to suggest we set type explicitly in the USER case too just
to make that abundantly clear rather than taking advantage of the
kzalloc struct.

> +
> +	ret = vfio_set_msi_aperture(iommu, iova, size);
> +	if (ret)
> +		goto free_unlock;
> +
> +	vfio_link_dma(iommu, dma);
> +	goto unlock;
> +
> +free_unlock:
> +	kfree(dma);
> +unlock:
> +	mutex_unlock(&iommu->lock);
> +	return ret;
> +}
> +
>  static int vfio_bus_type(struct device *dev, void *data)
>  {
>  	struct bus_type **bus = data;
> @@ -1062,7 +1134,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  	} else if (cmd == VFIO_IOMMU_MAP_DMA) {
>  		struct vfio_iommu_type1_dma_map map;
>  		uint32_t mask = VFIO_DMA_MAP_FLAG_READ |
> -				VFIO_DMA_MAP_FLAG_WRITE;
> +				VFIO_DMA_MAP_FLAG_WRITE |
> +				VFIO_DMA_MAP_FLAG_RESERVED_MSI_IOVA;
>  
>  		minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
>  
> @@ -1072,6 +1145,9 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  		if (map.argsz < minsz || map.flags & ~mask)
>  			return -EINVAL;
>  
> +		if (map.flags & VFIO_DMA_MAP_FLAG_RESERVED_MSI_IOVA)
> +			return vfio_register_msi_range(iommu, &map);
> +
>  		return vfio_dma_do_map(iommu, &map);
>  
>  	} else if (cmd == VFIO_IOMMU_UNMAP_DMA) {
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 255a211..4a9dbc2 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -498,12 +498,19 @@ struct vfio_iommu_type1_info {
>   *
>   * Map process virtual addresses to IO virtual addresses using the
>   * provided struct vfio_dma_map. Caller sets argsz. READ &/ WRITE required.
> + *
> + * In case RESERVED_MSI_IOVA flag is set, the API only aims at registering an
> + * IOVA region that will be used on some platforms to map the host MSI frames.
> + * In that specific case, vaddr is ignored. Once registered, an MSI reserved
> + * IOVA region stays until the container is closed.
>   */
>  struct vfio_iommu_type1_dma_map {
>  	__u32	argsz;
>  	__u32	flags;
>  #define VFIO_DMA_MAP_FLAG_READ (1 << 0)		/* readable from device */
>  #define VFIO_DMA_MAP_FLAG_WRITE (1 << 1)	/* writable from device */
> +/* reserved iova for MSI vectors*/
> +#define VFIO_DMA_MAP_FLAG_RESERVED_MSI_IOVA (1 << 2)
>  	__u64	vaddr;				/* Process virtual address */
>  	__u64	iova;				/* IO virtual address */
>  	__u64	size;				/* Size of mapping (bytes) */
> @@ -519,7 +526,8 @@ struct vfio_iommu_type1_dma_map {
>   * Caller sets argsz.  The actual unmapped size is returned in the size
>   * field.  No guarantee is made to the user that arbitrary unmaps of iova
>   * or size different from those used in the original mapping call will
> - * succeed.
> + * succeed. Once registered, an MSI region cannot be unmapped and stays
> + * until the container is closed.
>   */
>  struct vfio_iommu_type1_dma_unmap {
>  	__u32	argsz;