Re: [PATCH v6 2/5] vfio: allow the user to register reserved iova range for MSI mapping

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

On Mon,  4 Apr 2016 08:30:08 +0000
Eric Auger <eric.auger@linaro.org> wrote:

> The user is allowed to [un]register a reserved IOVA range by using the
> DMA MAP API and setting the new flag: VFIO_DMA_MAP_FLAG_MSI_RESERVED_IOVA.
> It provides the base address and the size. 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 the VFIO-PCI device allocates its MSIs.
> 
> This patch also handles the destruction of the reserved binding RB-tree and
> domain's iova_domains.
> 
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
> 
> ---
> 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.
> 
> Conflicts:
> 	drivers/vfio/vfio_iommu_type1.c
> ---
>  drivers/vfio/vfio_iommu_type1.c | 141 +++++++++++++++++++++++++++++++++++++++-
>  include/uapi/linux/vfio.h       |  12 +++-
>  2 files changed, 150 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index c9ddbde..4497b20 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/dma-reserved-iommu.h>
>  
>  #define DRIVER_VERSION  "0.2"
>  #define DRIVER_AUTHOR   "Alex Williamson <alex.williamson@redhat.com>"
> @@ -403,10 +404,22 @@ static void vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma)
>  	vfio_lock_acct(-unlocked);
>  }
>  
> +static void vfio_unmap_reserved(struct vfio_iommu *iommu)
> +{
> +#ifdef CONFIG_IOMMU_DMA_RESERVED
> +	struct vfio_domain *d;
> +
> +	list_for_each_entry(d, &iommu->domain_list, next)
> +		iommu_unmap_reserved(d->domain);
> +#endif
> +}
> +
>  static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
>  {
>  	if (likely(dma->type != VFIO_IOVA_RESERVED))
>  		vfio_unmap_unpin(iommu, dma);
> +	else
> +		vfio_unmap_reserved(iommu);
>  	vfio_unlink_dma(iommu, dma);
>  	kfree(dma);
>  }

This makes me nervous, apparently we can add reserved mappings
individually, but we have absolutely no granularity on remove, so if we
remove one, we've removed them all even though we still have them
linked in our rb tree.  I see later that only one reserved region is
allowed, but that seems very short sighted, especially to impose that
on the user level API.

> @@ -489,7 +502,8 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>  	 */
>  	if (iommu->v2) {
>  		dma = vfio_find_dma(iommu, unmap->iova, 0);
> -		if (dma && dma->iova != unmap->iova) {
> +		if (dma && (dma->iova != unmap->iova ||
> +			   (dma->type == VFIO_IOVA_RESERVED))) {

This seems unnecessary, won't the reserved entries fall out in the
while loop below?

>  			ret = -EINVAL;
>  			goto unlock;
>  		}
> @@ -501,6 +515,10 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>  	}
>  
>  	while ((dma = vfio_find_dma(iommu, unmap->iova, unmap->size))) {
> +		if (dma->type == VFIO_IOVA_RESERVED) {
> +			ret = -EINVAL;
> +			goto unlock;
> +		}

Hmm, API concerns here.  Previously a user could unmap from iova = 0 to
size = 2^64 - 1 and expect all mappings to get cleared.  Now they can't
do that if they've registered any reserved regions.  Seems like maybe
we should ignore it and continue instead of abort, but then we need to
change the parameters of vfio_find_dma() to get it to move on, or pass
the type to the function, which would prevent us from getting here in
the first place.

>  		if (!iommu->v2 && unmap->iova > dma->iova)
>  			break;
>  		unmapped += dma->size;
> @@ -650,6 +668,114 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>  	return ret;
>  }
>  
> +static int vfio_register_reserved_iova_range(struct vfio_iommu *iommu,
> +			   struct vfio_iommu_type1_dma_map *map)
> +{
> +#ifdef CONFIG_IOMMU_DMA_RESERVED
> +	dma_addr_t iova = map->iova;
> +	size_t size = map->size;
> +	uint64_t mask;
> +	struct vfio_dma *dma;
> +	int ret = 0;
> +	struct vfio_domain *d;
> +	unsigned long order;
> +
> +	/* 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)) {
> +		ret =  -EEXIST;
> +		goto out;
> +	}
> +
> +	dma = kzalloc(sizeof(*dma), GFP_KERNEL);
> +	if (!dma) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	dma->iova = iova;
> +	dma->size = size;
> +	dma->type = VFIO_IOVA_RESERVED;
> +
> +	list_for_each_entry(d, &iommu->domain_list, next)
> +		ret |= iommu_alloc_reserved_iova_domain(d->domain, iova,
> +							size, order);
> +
> +	if (ret) {
> +		list_for_each_entry(d, &iommu->domain_list, next)
> +			iommu_free_reserved_iova_domain(d->domain);
> +		goto out;
> +	}
> +
> +	vfio_link_dma(iommu, dma);
> +
> +out:
> +	mutex_unlock(&iommu->lock);
> +	return ret;
> +#else /* CONFIG_IOMMU_DMA_RESERVED */
> +	return -ENODEV;
> +#endif
> +}
> +
> +static void vfio_unregister_reserved_iova_range(struct vfio_iommu *iommu,
> +				struct vfio_iommu_type1_dma_unmap *unmap)
> +{
> +#ifdef CONFIG_IOMMU_DMA_RESERVED
> +	dma_addr_t iova = unmap->iova;
> +	struct vfio_dma *dma;
> +	size_t size = unmap->size;
> +	uint64_t mask;
> +	unsigned long order;
> +
> +	/* Verify that none of our __u64 fields overflow */
> +	if (unmap->size != size || unmap->iova != iova)
> +		return;
> +
> +	order =  __ffs(vfio_pgsize_bitmap(iommu));
> +	mask = ((uint64_t)1 << order) - 1;
> +
> +	WARN_ON(mask & PAGE_MASK);
> +
> +	if (!size || (size | iova) & mask)
> +		return;
> +
> +	/* Don't allow IOVA address wrap */
> +	if (iova + size - 1 < iova)
> +		return;
> +
> +	mutex_lock(&iommu->lock);
> +
> +	dma = vfio_find_dma(iommu, iova, size);
> +
> +	if (!dma || (dma->type != VFIO_IOVA_RESERVED)) {
> +		unmap->size = 0;
> +		goto out;
> +	}
> +
> +	unmap->size =  dma->size;
> +	vfio_remove_dma(iommu, dma);
> +
> +out:
> +	mutex_unlock(&iommu->lock);
> +#endif

Having a find_dma that accepts a type and a remove_reserved here seems
like it might simplify things.

> +}
> +
>  static int vfio_bus_type(struct device *dev, void *data)
>  {
>  	struct bus_type **bus = data;
> @@ -946,6 +1072,7 @@ static void vfio_iommu_type1_release(void *iommu_data)
>  	struct vfio_group *group, *group_tmp;
>  
>  	vfio_iommu_unmap_unpin_all(iommu);
> +	vfio_unmap_reserved(iommu);

If we call vfio_unmap_reserved() here, then why does vfio_remove_dma()
need to handle reserved entries?  We might as well have a separate
vfio_remove_reserved_dma().

>  
>  	list_for_each_entry_safe(domain, domain_tmp,
>  				 &iommu->domain_list, next) {
> @@ -1020,7 +1147,8 @@ 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_MSI_RESERVED_IOVA;
>  
>  		minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
>  
> @@ -1030,6 +1158,9 @@ 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_MSI_RESERVED_IOVA)
> +			return vfio_register_reserved_iova_range(iommu, &map);
> +
>  		return vfio_dma_do_map(iommu, &map);
>  
>  	} else if (cmd == VFIO_IOMMU_UNMAP_DMA) {
> @@ -1044,10 +1175,16 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  		if (unmap.argsz < minsz || unmap.flags)
>  			return -EINVAL;
>  
> +		if (unmap.flags & VFIO_DMA_MAP_FLAG_MSI_RESERVED_IOVA) {
> +			vfio_unregister_reserved_iova_range(iommu, &unmap);
> +			goto out;
> +		}
> +
>  		ret = vfio_dma_do_unmap(iommu, &unmap);
>  		if (ret)
>  			return ret;
>  
> +out:
>  		return copy_to_user((void __user *)arg, &unmap, minsz) ?
>  			-EFAULT : 0;
>  	}
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 255a211..a49be8a 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -498,12 +498,21 @@ 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 MSI_RESERVED_IOVA flag is set, the API only aims at registering an
> + * IOVA region which will be used on some platforms to map the host MSI frame.
> + * in that specific case, vaddr and prot are ignored. The requirement for
> + * provisioning such IOVA range can be checked by calling VFIO_IOMMU_GET_INFO
> + * with the VFIO_IOMMU_INFO_REQUIRE_MSI_MAP attribute. A single
> + * MSI_RESERVED_IOVA region can be registered
>   */

Why do we ignore read/write flags?  I'm not sure how useful a read-only
reserved region might be, but certainly some platforms might support
write-only or read-write.  Isn't this something we should let the IOMMU
driver decide?  ie. pass it down and let it fail or not?  Also why are
we making it the API spec to only allow a single reserved region of
this type?  We could simply let additional ones fail, or better yet add
a capability to the info ioctl to indicate the number available and
then fail if the user exceeds it.

>  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_MSI_RESERVED_IOVA (1 << 2)

nit, ...RESERVED_MSI_IOVA makes a tad more sense and if we add new
reserved flags seems like it puts the precedence in order.

>  	__u64	vaddr;				/* Process virtual address */
>  	__u64	iova;				/* IO virtual address */
>  	__u64	size;				/* Size of mapping (bytes) */
> @@ -519,7 +528,8 @@ 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. A Reserved DMA region must be unmapped with MSI_RESERVED_IOVA
> + * flag set.

So map/unmap become bi-modal, with this flag set they should only
operate on reserved entries, otherwise they should operate on legacy
entries.  So clearly as a user I should be able to continue doing an
unmap from 0-(-1) of legacy entries and not stumble over reserved
entries.  Thanks,

Alex