[PATCH V3 0/5] fixes for virtual address update

[PATCH V3 0/5] fixes for virtual address update

[Steve Sistare]

Fix bugs in the interfaces that allow the underlying memory object of an
iova range to be mapped in a new address space.  They allow userland to
indefinitely block vfio mediated device kernel threads, and do not
propagate the locked_vm count to a new mm.

The fixes impose restrictions that eliminate waiting conditions, so
revert the dead code:
  commit 898b9eaeb3fe ("vfio/type1: block on invalid vaddr")
  commit 487ace134053 ("vfio/type1: implement notify callback")
  commit ec5e32940cc9 ("vfio: iommu driver notify callback")

Changes in V2 (thanks Alex):
  * do not allow group attach while vaddrs are invalid
  * add patches to delete dead code
  * add WARN_ON for never-should-happen conditions
  * check for changed mm in unmap.
  * check for vfio_lock_acct failure in remap

Changes in V3 (ditto!):
  * return errno at WARN_ON sites, and make it unique
  * correctly check for dma task mm change
  * change dma owner to current when vaddr is updated
  * add Fixes to commit messages
  * refactored new code in vfio_dma_do_map

Steve Sistare (5):
  vfio/type1: exclude mdevs from VFIO_UPDATE_VADDR
  vfio/type1: prevent locked_vm underflow
  vfio/type1: revert "block on invalid vaddr"
  vfio/type1: revert "implement notify callback"
  vfio: revert "iommu driver notify callback"

 drivers/vfio/container.c        |   5 --
 drivers/vfio/vfio.h             |   7 --
 drivers/vfio/vfio_iommu_type1.c | 193 +++++++++++++++++++---------------------
 include/uapi/linux/vfio.h       |  15 ++--
 4 files changed, 99 insertions(+), 121 deletions(-)

-- 
1.8.3.1

[PATCH V3 1/5] vfio/type1: exclude mdevs from VFIO_UPDATE_VADDR

[Steve Sistare]

Disable the VFIO_UPDATE_VADDR capability if mediated devices are present.
Their kernel threads could be blocked indefinitely by a misbehaving
userland while trying to pin/unpin pages while vaddrs are being updated.

Do not allow groups to be added to the container while vaddr's are invalid,
so we never need to block user threads from pinning, and can delete the
vaddr-waiting code in a subsequent patch.

Fixes: c3cbab24db38 ("vfio/type1: implement interfaces to update vaddr")

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 drivers/vfio/vfio_iommu_type1.c | 41 +++++++++++++++++++++++++++++++++++++++--
 include/uapi/linux/vfio.h       | 15 +++++++++------
 2 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 23c24fe..b04f485 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -861,6 +861,12 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
 
 	mutex_lock(&iommu->lock);
 
+	if (iommu->vaddr_invalid_count) {
+		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
+		ret = -EIO;
+		goto pin_done;
+	}
+
 	/*
 	 * Wait for all necessary vaddr's to be valid so they can be used in
 	 * the main loop without dropping the lock, to avoid racing vs unmap.
@@ -1343,6 +1349,12 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
 
 	mutex_lock(&iommu->lock);
 
+	/* Cannot update vaddr if mdev is present. */
+	if (invalidate_vaddr && !list_empty(&iommu->emulated_iommu_groups)) {
+		ret = -EIO;
+		goto unlock;
+	}
+
 	pgshift = __ffs(iommu->pgsize_bitmap);
 	pgsize = (size_t)1 << pgshift;
 
@@ -2185,11 +2197,16 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
 	struct iommu_domain_geometry *geo;
 	LIST_HEAD(iova_copy);
 	LIST_HEAD(group_resv_regions);
-	int ret = -EINVAL;
+	int ret = -EIO;
 
 	mutex_lock(&iommu->lock);
 
+	/* Attach could require pinning, so disallow while vaddr is invalid. */
+	if (iommu->vaddr_invalid_count)
+		goto out_unlock;
+
 	/* Check for duplicates */
+	ret = -EINVAL;
 	if (vfio_iommu_find_iommu_group(iommu, iommu_group))
 		goto out_unlock;
 
@@ -2660,6 +2677,16 @@ static int vfio_domains_have_enforce_cache_coherency(struct vfio_iommu *iommu)
 	return ret;
 }
 
+static int vfio_iommu_has_emulated(struct vfio_iommu *iommu)
+{
+	int ret;
+
+	mutex_lock(&iommu->lock);
+	ret = !list_empty(&iommu->emulated_iommu_groups);
+	mutex_unlock(&iommu->lock);
+	return ret;
+}
+
 static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
 					    unsigned long arg)
 {
@@ -2668,8 +2695,13 @@ static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
 	case VFIO_TYPE1v2_IOMMU:
 	case VFIO_TYPE1_NESTING_IOMMU:
 	case VFIO_UNMAP_ALL:
-	case VFIO_UPDATE_VADDR:
 		return 1;
+	case VFIO_UPDATE_VADDR:
+		/*
+		 * Disable this feature if mdevs are present.  They cannot
+		 * safely pin/unpin while vaddrs are being updated.
+		 */
+		return iommu && !vfio_iommu_has_emulated(iommu);
 	case VFIO_DMA_CC_IOMMU:
 		if (!iommu)
 			return 0;
@@ -3080,6 +3112,11 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
 	size_t offset;
 	int ret;
 
+	if (iommu->vaddr_invalid_count) {
+		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
+		return -EIO;
+	}
+
 	*copied = 0;
 
 	ret = vfio_find_dma_valid(iommu, user_iova, 1, &dma);
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index d7d8e09..4e8d344 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -49,7 +49,11 @@
 /* Supports VFIO_DMA_UNMAP_FLAG_ALL */
 #define VFIO_UNMAP_ALL			9
 
-/* Supports the vaddr flag for DMA map and unmap */
+/*
+ * Supports the vaddr flag for DMA map and unmap.  Not supported for mediated
+ * devices, so this capability is subject to change as groups are added or
+ * removed.
+ */
 #define VFIO_UPDATE_VADDR		10
 
 /*
@@ -1215,8 +1219,7 @@ struct vfio_iommu_type1_info_dma_avail {
  * Map process virtual addresses to IO virtual addresses using the
  * provided struct vfio_dma_map. Caller sets argsz. READ &/ WRITE required.
  *
- * If flags & VFIO_DMA_MAP_FLAG_VADDR, update the base vaddr for iova, and
- * unblock translation of host virtual addresses in the iova range.  The vaddr
+ * If flags & VFIO_DMA_MAP_FLAG_VADDR, update the base vaddr for iova. The vaddr
  * must have previously been invalidated with VFIO_DMA_UNMAP_FLAG_VADDR.  To
  * maintain memory consistency within the user application, the updated vaddr
  * must address the same memory object as originally mapped.  Failure to do so
@@ -1267,9 +1270,9 @@ struct vfio_bitmap {
  * must be 0.  This cannot be combined with the get-dirty-bitmap flag.
  *
  * If flags & VFIO_DMA_UNMAP_FLAG_VADDR, do not unmap, but invalidate host
- * virtual addresses in the iova range.  Tasks that attempt to translate an
- * iova's vaddr will block.  DMA to already-mapped pages continues.  This
- * cannot be combined with the get-dirty-bitmap flag.
+ * virtual addresses in the iova range.  DMA to already-mapped pages continues.
+ * Groups may not be added to the container while any addresses are invalid.
+ * This cannot be combined with the get-dirty-bitmap flag.
  */
 struct vfio_iommu_type1_dma_unmap {
 	__u32	argsz;
-- 
1.8.3.1

Re: [PATCH V3 1/5] vfio/type1: exclude mdevs from VFIO_UPDATE_VADDR

[Alex Williamson]

On Wed, 14 Dec 2022 11:22:47 -0800
Steve Sistare <steven.sistare@oracle.com> wrote:

> Disable the VFIO_UPDATE_VADDR capability if mediated devices are present.
> Their kernel threads could be blocked indefinitely by a misbehaving
> userland while trying to pin/unpin pages while vaddrs are being updated.
> 
> Do not allow groups to be added to the container while vaddr's are invalid,
> so we never need to block user threads from pinning, and can delete the
> vaddr-waiting code in a subsequent patch.
> 
> Fixes: c3cbab24db38 ("vfio/type1: implement interfaces to update vaddr")
> 
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 41 +++++++++++++++++++++++++++++++++++++++--
>  include/uapi/linux/vfio.h       | 15 +++++++++------
>  2 files changed, 48 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 23c24fe..b04f485 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -861,6 +861,12 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>  
>  	mutex_lock(&iommu->lock);
>  
> +	if (iommu->vaddr_invalid_count) {
> +		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
> +		ret = -EIO;
> +		goto pin_done;
> +	}
> +

This simplifies to:

	if (WARN_ONCE(iommu->vaddr_invalid_count,
		      "mdev not allowed	with VFIO_UPDATE_VADDR\n")) {
		ret = -EIO;
		goto pin_done;
	}

I was sort of figuring this would be a -EPERM or -EBUSY, maybe even
-EAGAIN, though perhaps it's academic which errno to return if we
should never get here.

>  	/*
>  	 * Wait for all necessary vaddr's to be valid so they can be used in
>  	 * the main loop without dropping the lock, to avoid racing vs unmap.
> @@ -1343,6 +1349,12 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>  
>  	mutex_lock(&iommu->lock);
>  
> +	/* Cannot update vaddr if mdev is present. */
> +	if (invalidate_vaddr && !list_empty(&iommu->emulated_iommu_groups)) {
> +		ret = -EIO;
> +		goto unlock;
> +	}
> +

On the other hand, this errno is reachable by the user, and I'm not
sure -EIO is the best choice for a condition that's blocked due to use
configuration.

>  	pgshift = __ffs(iommu->pgsize_bitmap);
>  	pgsize = (size_t)1 << pgshift;
>  
> @@ -2185,11 +2197,16 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>  	struct iommu_domain_geometry *geo;
>  	LIST_HEAD(iova_copy);
>  	LIST_HEAD(group_resv_regions);
> -	int ret = -EINVAL;
> +	int ret = -EIO;
>  
>  	mutex_lock(&iommu->lock);
>  
> +	/* Attach could require pinning, so disallow while vaddr is invalid. */
> +	if (iommu->vaddr_invalid_count)
> +		goto out_unlock;
> +

Also user reachable, so should track if we pick another errno.

>  	/* Check for duplicates */
> +	ret = -EINVAL;
>  	if (vfio_iommu_find_iommu_group(iommu, iommu_group))
>  		goto out_unlock;
>  
> @@ -2660,6 +2677,16 @@ static int vfio_domains_have_enforce_cache_coherency(struct vfio_iommu *iommu)
>  	return ret;
>  }
>  
> +static int vfio_iommu_has_emulated(struct vfio_iommu *iommu)
> +{
> +	int ret;
> +
> +	mutex_lock(&iommu->lock);
> +	ret = !list_empty(&iommu->emulated_iommu_groups);
> +	mutex_unlock(&iommu->lock);
> +	return ret;
> +}

Nit, this could return bool.  I suppose it doesn't because the below
returns int, but it seems we're already in the realm of creating a
boolean value there.

> +
>  static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
>  					    unsigned long arg)
>  {
> @@ -2668,8 +2695,13 @@ static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
>  	case VFIO_TYPE1v2_IOMMU:
>  	case VFIO_TYPE1_NESTING_IOMMU:
>  	case VFIO_UNMAP_ALL:
> -	case VFIO_UPDATE_VADDR:
>  		return 1;
> +	case VFIO_UPDATE_VADDR:
> +		/*
> +		 * Disable this feature if mdevs are present.  They cannot
> +		 * safely pin/unpin while vaddrs are being updated.
> +		 */
> +		return iommu && !vfio_iommu_has_emulated(iommu);
>  	case VFIO_DMA_CC_IOMMU:
>  		if (!iommu)
>  			return 0;
> @@ -3080,6 +3112,11 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
>  	size_t offset;
>  	int ret;
>  
> +	if (iommu->vaddr_invalid_count) {
> +		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
> +		return -EIO;
> +	}

Same optimization above, but why are we letting the code iterate this
multiple times in the _chunk function rather than testing once in the
caller?  Thanks,

Alex

> +
>  	*copied = 0;
>  
>  	ret = vfio_find_dma_valid(iommu, user_iova, 1, &dma);
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index d7d8e09..4e8d344 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -49,7 +49,11 @@
>  /* Supports VFIO_DMA_UNMAP_FLAG_ALL */
>  #define VFIO_UNMAP_ALL			9
>  
> -/* Supports the vaddr flag for DMA map and unmap */
> +/*
> + * Supports the vaddr flag for DMA map and unmap.  Not supported for mediated
> + * devices, so this capability is subject to change as groups are added or
> + * removed.
> + */
>  #define VFIO_UPDATE_VADDR		10
>  
>  /*
> @@ -1215,8 +1219,7 @@ struct vfio_iommu_type1_info_dma_avail {
>   * Map process virtual addresses to IO virtual addresses using the
>   * provided struct vfio_dma_map. Caller sets argsz. READ &/ WRITE required.
>   *
> - * If flags & VFIO_DMA_MAP_FLAG_VADDR, update the base vaddr for iova, and
> - * unblock translation of host virtual addresses in the iova range.  The vaddr
> + * If flags & VFIO_DMA_MAP_FLAG_VADDR, update the base vaddr for iova. The vaddr
>   * must have previously been invalidated with VFIO_DMA_UNMAP_FLAG_VADDR.  To
>   * maintain memory consistency within the user application, the updated vaddr
>   * must address the same memory object as originally mapped.  Failure to do so
> @@ -1267,9 +1270,9 @@ struct vfio_bitmap {
>   * must be 0.  This cannot be combined with the get-dirty-bitmap flag.
>   *
>   * If flags & VFIO_DMA_UNMAP_FLAG_VADDR, do not unmap, but invalidate host
> - * virtual addresses in the iova range.  Tasks that attempt to translate an
> - * iova's vaddr will block.  DMA to already-mapped pages continues.  This
> - * cannot be combined with the get-dirty-bitmap flag.
> + * virtual addresses in the iova range.  DMA to already-mapped pages continues.
> + * Groups may not be added to the container while any addresses are invalid.
> + * This cannot be combined with the get-dirty-bitmap flag.
>   */
>  struct vfio_iommu_type1_dma_unmap {
>  	__u32	argsz;

Re: [PATCH V3 1/5] vfio/type1: exclude mdevs from VFIO_UPDATE_VADDR

[Steven Sistare]

On 12/14/2022 2:40 PM, Alex Williamson wrote:
> On Wed, 14 Dec 2022 11:22:47 -0800
> Steve Sistare <steven.sistare@oracle.com> wrote:
> 
>> Disable the VFIO_UPDATE_VADDR capability if mediated devices are present.
>> Their kernel threads could be blocked indefinitely by a misbehaving
>> userland while trying to pin/unpin pages while vaddrs are being updated.
>>
>> Do not allow groups to be added to the container while vaddr's are invalid,
>> so we never need to block user threads from pinning, and can delete the
>> vaddr-waiting code in a subsequent patch.
>>
>> Fixes: c3cbab24db38 ("vfio/type1: implement interfaces to update vaddr")
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 41 +++++++++++++++++++++++++++++++++++++++--
>>  include/uapi/linux/vfio.h       | 15 +++++++++------
>>  2 files changed, 48 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 23c24fe..b04f485 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -861,6 +861,12 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>>  
>>  	mutex_lock(&iommu->lock);
>>  
>> +	if (iommu->vaddr_invalid_count) {
>> +		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
>> +		ret = -EIO;
>> +		goto pin_done;
>> +	}
>> +
> 
> This simplifies to:
> 
> 	if (WARN_ONCE(iommu->vaddr_invalid_count,
> 		      "mdev not allowed	with VFIO_UPDATE_VADDR\n")) {
> 		ret = -EIO;
> 		goto pin_done;
> 	}

Will do, thanks.  It's a new idiom for me.

> I was sort of figuring this would be a -EPERM or -EBUSY, maybe even
> -EAGAIN, though perhaps it's academic which errno to return if we
> should never get here.

Not EAGAIN.  That implies they should retry, but we don't want them to keep
retrying until userland (never) remaps the vaddr.

EPERM is returned for other reasons, particularly in vfio_iommu_type1_dma_rw_chunk,
where we would like to return something unique for this condition. 

EBUSY sounds good, here and in the other locations.
 
>>  	/*
>>  	 * Wait for all necessary vaddr's to be valid so they can be used in
>>  	 * the main loop without dropping the lock, to avoid racing vs unmap.
>> @@ -1343,6 +1349,12 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>  
>>  	mutex_lock(&iommu->lock);
>>  
>> +	/* Cannot update vaddr if mdev is present. */
>> +	if (invalidate_vaddr && !list_empty(&iommu->emulated_iommu_groups)) {
>> +		ret = -EIO;
>> +		goto unlock;
>> +	}
>> +
> 
> On the other hand, this errno is reachable by the user, and I'm not
> sure -EIO is the best choice for a condition that's blocked due to use
> configuration.
>>  	pgshift = __ffs(iommu->pgsize_bitmap);
>>  	pgsize = (size_t)1 << pgshift;
>>  
>> @@ -2185,11 +2197,16 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>>  	struct iommu_domain_geometry *geo;
>>  	LIST_HEAD(iova_copy);
>>  	LIST_HEAD(group_resv_regions);
>> -	int ret = -EINVAL;
>> +	int ret = -EIO;
>>  
>>  	mutex_lock(&iommu->lock);
>>  
>> +	/* Attach could require pinning, so disallow while vaddr is invalid. */
>> +	if (iommu->vaddr_invalid_count)
>> +		goto out_unlock;
>> +
> 
> Also user reachable, so should track if we pick another errno.
> 
>>  	/* Check for duplicates */
>> +	ret = -EINVAL;
>>  	if (vfio_iommu_find_iommu_group(iommu, iommu_group))
>>  		goto out_unlock;
>>  
>> @@ -2660,6 +2677,16 @@ static int vfio_domains_have_enforce_cache_coherency(struct vfio_iommu *iommu)
>>  	return ret;
>>  }
>>  
>> +static int vfio_iommu_has_emulated(struct vfio_iommu *iommu)
>> +{
>> +	int ret;
>> +
>> +	mutex_lock(&iommu->lock);
>> +	ret = !list_empty(&iommu->emulated_iommu_groups);
>> +	mutex_unlock(&iommu->lock);
>> +	return ret;
>> +}
> 
> Nit, this could return bool.  

OK.

> I suppose it doesn't because the below
> returns int, but it seems we're already in the realm of creating a
> boolean value there.
> 
>> +
>>  static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
>>  					    unsigned long arg)
>>  {
>> @@ -2668,8 +2695,13 @@ static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
>>  	case VFIO_TYPE1v2_IOMMU:
>>  	case VFIO_TYPE1_NESTING_IOMMU:
>>  	case VFIO_UNMAP_ALL:
>> -	case VFIO_UPDATE_VADDR:
>>  		return 1;
>> +	case VFIO_UPDATE_VADDR:
>> +		/*
>> +		 * Disable this feature if mdevs are present.  They cannot
>> +		 * safely pin/unpin while vaddrs are being updated.
>> +		 */
>> +		return iommu && !vfio_iommu_has_emulated(iommu);
>>  	case VFIO_DMA_CC_IOMMU:
>>  		if (!iommu)
>>  			return 0;
>> @@ -3080,6 +3112,11 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
>>  	size_t offset;
>>  	int ret;
>>  
>> +	if (iommu->vaddr_invalid_count) {
>> +		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
>> +		return -EIO;
>> +	}
> 
> Same optimization above, but why are we letting the code iterate this
> multiple times in the _chunk function rather than testing once in the
> caller?  Thanks,

An oversight, I'll hoist it.

- Steve

>> +
>>  	*copied = 0;
>>  
>>  	ret = vfio_find_dma_valid(iommu, user_iova, 1, &dma);
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index d7d8e09..4e8d344 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -49,7 +49,11 @@
>>  /* Supports VFIO_DMA_UNMAP_FLAG_ALL */
>>  #define VFIO_UNMAP_ALL			9
>>  
>> -/* Supports the vaddr flag for DMA map and unmap */
>> +/*
>> + * Supports the vaddr flag for DMA map and unmap.  Not supported for mediated
>> + * devices, so this capability is subject to change as groups are added or
>> + * removed.
>> + */
>>  #define VFIO_UPDATE_VADDR		10
>>  
>>  /*
>> @@ -1215,8 +1219,7 @@ struct vfio_iommu_type1_info_dma_avail {
>>   * Map process virtual addresses to IO virtual addresses using the
>>   * provided struct vfio_dma_map. Caller sets argsz. READ &/ WRITE required.
>>   *
>> - * If flags & VFIO_DMA_MAP_FLAG_VADDR, update the base vaddr for iova, and
>> - * unblock translation of host virtual addresses in the iova range.  The vaddr
>> + * If flags & VFIO_DMA_MAP_FLAG_VADDR, update the base vaddr for iova. The vaddr
>>   * must have previously been invalidated with VFIO_DMA_UNMAP_FLAG_VADDR.  To
>>   * maintain memory consistency within the user application, the updated vaddr
>>   * must address the same memory object as originally mapped.  Failure to do so
>> @@ -1267,9 +1270,9 @@ struct vfio_bitmap {
>>   * must be 0.  This cannot be combined with the get-dirty-bitmap flag.
>>   *
>>   * If flags & VFIO_DMA_UNMAP_FLAG_VADDR, do not unmap, but invalidate host
>> - * virtual addresses in the iova range.  Tasks that attempt to translate an
>> - * iova's vaddr will block.  DMA to already-mapped pages continues.  This
>> - * cannot be combined with the get-dirty-bitmap flag.
>> + * virtual addresses in the iova range.  DMA to already-mapped pages continues.
>> + * Groups may not be added to the container while any addresses are invalid.
>> + * This cannot be combined with the get-dirty-bitmap flag.
>>   */
>>  struct vfio_iommu_type1_dma_unmap {
>>  	__u32	argsz;
> 

Re: [PATCH V3 1/5] vfio/type1: exclude mdevs from VFIO_UPDATE_VADDR

[Steven Sistare]

On 12/14/2022 3:03 PM, Steven Sistare wrote:
> On 12/14/2022 2:40 PM, Alex Williamson wrote:
>> On Wed, 14 Dec 2022 11:22:47 -0800
>> Steve Sistare <steven.sistare@oracle.com> wrote:
>>
>>> Disable the VFIO_UPDATE_VADDR capability if mediated devices are present.
>>> Their kernel threads could be blocked indefinitely by a misbehaving
>>> userland while trying to pin/unpin pages while vaddrs are being updated.
>>>
>>> Do not allow groups to be added to the container while vaddr's are invalid,
>>> so we never need to block user threads from pinning, and can delete the
>>> vaddr-waiting code in a subsequent patch.
>>>
>>> Fixes: c3cbab24db38 ("vfio/type1: implement interfaces to update vaddr")
>>>
>>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>>> ---
>>>  drivers/vfio/vfio_iommu_type1.c | 41 +++++++++++++++++++++++++++++++++++++++--
>>>  include/uapi/linux/vfio.h       | 15 +++++++++------
>>>  2 files changed, 48 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>>> index 23c24fe..b04f485 100644
>>> --- a/drivers/vfio/vfio_iommu_type1.c
>>> +++ b/drivers/vfio/vfio_iommu_type1.c
>>> @@ -861,6 +861,12 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>>>  
>>>  	mutex_lock(&iommu->lock);
>>>  
>>> +	if (iommu->vaddr_invalid_count) {
>>> +		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
>>> +		ret = -EIO;
>>> +		goto pin_done;
>>> +	}
>>> +
>>
>> This simplifies to:
>>
>> 	if (WARN_ONCE(iommu->vaddr_invalid_count,
>> 		      "mdev not allowed	with VFIO_UPDATE_VADDR\n")) {
>> 		ret = -EIO;
>> 		goto pin_done;
>> 	}
> 
> Will do, thanks.  It's a new idiom for me.
> 
>> I was sort of figuring this would be a -EPERM or -EBUSY, maybe even
>> -EAGAIN, though perhaps it's academic which errno to return if we
>> should never get here.
> 
> Not EAGAIN.  That implies they should retry, but we don't want them to keep
> retrying until userland (never) remaps the vaddr.
> 
> EPERM is returned for other reasons, particularly in vfio_iommu_type1_dma_rw_chunk,
> where we would like to return something unique for this condition. 
> 
> EBUSY sounds good, here and in the other locations.
>  
>>>  	/*
>>>  	 * Wait for all necessary vaddr's to be valid so they can be used in
>>>  	 * the main loop without dropping the lock, to avoid racing vs unmap.
>>> @@ -1343,6 +1349,12 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>>  
>>>  	mutex_lock(&iommu->lock);
>>>  
>>> +	/* Cannot update vaddr if mdev is present. */
>>> +	if (invalidate_vaddr && !list_empty(&iommu->emulated_iommu_groups)) {
>>> +		ret = -EIO;
>>> +		goto unlock;
>>> +	}
>>> +
>>
>> On the other hand, this errno is reachable by the user, and I'm not
>> sure -EIO is the best choice for a condition that's blocked due to use
>> configuration.
>>>  	pgshift = __ffs(iommu->pgsize_bitmap);
>>>  	pgsize = (size_t)1 << pgshift;
>>>  
>>> @@ -2185,11 +2197,16 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>>>  	struct iommu_domain_geometry *geo;
>>>  	LIST_HEAD(iova_copy);
>>>  	LIST_HEAD(group_resv_regions);
>>> -	int ret = -EINVAL;
>>> +	int ret = -EIO;
>>>  
>>>  	mutex_lock(&iommu->lock);
>>>  
>>> +	/* Attach could require pinning, so disallow while vaddr is invalid. */
>>> +	if (iommu->vaddr_invalid_count)
>>> +		goto out_unlock;
>>> +
>>
>> Also user reachable, so should track if we pick another errno.
>>
>>>  	/* Check for duplicates */
>>> +	ret = -EINVAL;
>>>  	if (vfio_iommu_find_iommu_group(iommu, iommu_group))
>>>  		goto out_unlock;
>>>  
>>> @@ -2660,6 +2677,16 @@ static int vfio_domains_have_enforce_cache_coherency(struct vfio_iommu *iommu)
>>>  	return ret;
>>>  }
>>>  
>>> +static int vfio_iommu_has_emulated(struct vfio_iommu *iommu)
>>> +{
>>> +	int ret;
>>> +
>>> +	mutex_lock(&iommu->lock);
>>> +	ret = !list_empty(&iommu->emulated_iommu_groups);
>>> +	mutex_unlock(&iommu->lock);
>>> +	return ret;
>>> +}
>>
>> Nit, this could return bool.  
> 
> OK.
> 
>> I suppose it doesn't because the below
>> returns int, but it seems we're already in the realm of creating a
>> boolean value there.
>>
>>> +
>>>  static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
>>>  					    unsigned long arg)
>>>  {
>>> @@ -2668,8 +2695,13 @@ static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
>>>  	case VFIO_TYPE1v2_IOMMU:
>>>  	case VFIO_TYPE1_NESTING_IOMMU:
>>>  	case VFIO_UNMAP_ALL:
>>> -	case VFIO_UPDATE_VADDR:
>>>  		return 1;
>>> +	case VFIO_UPDATE_VADDR:
>>> +		/*
>>> +		 * Disable this feature if mdevs are present.  They cannot
>>> +		 * safely pin/unpin while vaddrs are being updated.
>>> +		 */
>>> +		return iommu && !vfio_iommu_has_emulated(iommu);
>>>  	case VFIO_DMA_CC_IOMMU:
>>>  		if (!iommu)
>>>  			return 0;
>>> @@ -3080,6 +3112,11 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
>>>  	size_t offset;
>>>  	int ret;
>>>  
>>> +	if (iommu->vaddr_invalid_count) {
>>> +		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
>>> +		return -EIO;
>>> +	}
>>
>> Same optimization above, but why are we letting the code iterate this
>> multiple times in the _chunk function rather than testing once in the
>> caller?  Thanks,
> 
> An oversight, I'll hoist it.

It's actually a little nicer to leave the test here.  The first call to
here returns failure, and the caller exits the loop.  

Hoisting it requires jumping to an out label that releases the iommu lock.

Which do you prefer?

- Steve
>>> +
>>>  	*copied = 0;
>>>  
>>>  	ret = vfio_find_dma_valid(iommu, user_iova, 1, &dma);
>>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>>> index d7d8e09..4e8d344 100644
>>> --- a/include/uapi/linux/vfio.h
>>> +++ b/include/uapi/linux/vfio.h
>>> @@ -49,7 +49,11 @@
>>>  /* Supports VFIO_DMA_UNMAP_FLAG_ALL */
>>>  #define VFIO_UNMAP_ALL			9
>>>  
>>> -/* Supports the vaddr flag for DMA map and unmap */
>>> +/*
>>> + * Supports the vaddr flag for DMA map and unmap.  Not supported for mediated
>>> + * devices, so this capability is subject to change as groups are added or
>>> + * removed.
>>> + */
>>>  #define VFIO_UPDATE_VADDR		10
>>>  
>>>  /*
>>> @@ -1215,8 +1219,7 @@ struct vfio_iommu_type1_info_dma_avail {
>>>   * Map process virtual addresses to IO virtual addresses using the
>>>   * provided struct vfio_dma_map. Caller sets argsz. READ &/ WRITE required.
>>>   *
>>> - * If flags & VFIO_DMA_MAP_FLAG_VADDR, update the base vaddr for iova, and
>>> - * unblock translation of host virtual addresses in the iova range.  The vaddr
>>> + * If flags & VFIO_DMA_MAP_FLAG_VADDR, update the base vaddr for iova. The vaddr
>>>   * must have previously been invalidated with VFIO_DMA_UNMAP_FLAG_VADDR.  To
>>>   * maintain memory consistency within the user application, the updated vaddr
>>>   * must address the same memory object as originally mapped.  Failure to do so
>>> @@ -1267,9 +1270,9 @@ struct vfio_bitmap {
>>>   * must be 0.  This cannot be combined with the get-dirty-bitmap flag.
>>>   *
>>>   * If flags & VFIO_DMA_UNMAP_FLAG_VADDR, do not unmap, but invalidate host
>>> - * virtual addresses in the iova range.  Tasks that attempt to translate an
>>> - * iova's vaddr will block.  DMA to already-mapped pages continues.  This
>>> - * cannot be combined with the get-dirty-bitmap flag.
>>> + * virtual addresses in the iova range.  DMA to already-mapped pages continues.
>>> + * Groups may not be added to the container while any addresses are invalid.
>>> + * This cannot be combined with the get-dirty-bitmap flag.
>>>   */
>>>  struct vfio_iommu_type1_dma_unmap {
>>>  	__u32	argsz;
>>

Re: [PATCH V3 1/5] vfio/type1: exclude mdevs from VFIO_UPDATE_VADDR

[Alex Williamson]

On Wed, 14 Dec 2022 15:20:44 -0500
Steven Sistare <steven.sistare@oracle.com> wrote:

> On 12/14/2022 3:03 PM, Steven Sistare wrote:
> > On 12/14/2022 2:40 PM, Alex Williamson wrote:  
> >> On Wed, 14 Dec 2022 11:22:47 -0800
> >> Steve Sistare <steven.sistare@oracle.com> wrote:
> >>> @@ -3080,6 +3112,11 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
> >>>  	size_t offset;
> >>>  	int ret;
> >>>  
> >>> +	if (iommu->vaddr_invalid_count) {
> >>> +		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
> >>> +		return -EIO;
> >>> +	}  
> >>
> >> Same optimization above, but why are we letting the code iterate this
> >> multiple times in the _chunk function rather than testing once in the
> >> caller?  Thanks,  
> > 
> > An oversight, I'll hoist it.  
> 
> It's actually a little nicer to leave the test here.  The first call to
> here returns failure, and the caller exits the loop.  
> 
> Hoisting it requires jumping to an out label that releases the iommu lock.
> 
> Which do you prefer?

The failure might exit on the first chunk, but non-failure incurs
overhead per chunk.  I suspect we're not often iterating multiple
chunks, but I don't mind the goto in order to avoid that possibility.
Thanks,

Alex

[PATCH V3 2/5] vfio/type1: prevent locked_vm underflow

[Steve Sistare]

When a vfio container is preserved across exec using the VFIO_UPDATE_VADDR
interfaces, locked_vm of the new mm becomes 0.  If the user later unmaps a
dma mapping, locked_vm underflows to a large unsigned value, and a
subsequent dma map request fails with ENOMEM in __account_locked_vm.

To avoid underflow, do not decrement locked_vm during unmap if the
dma's mm has changed.  To restore the correct locked_vm count, when
VFIO_DMA_MAP_FLAG_VADDR is used and the dma's mm has changed, add
the mapping's pinned page count to the new mm->locked_vm, subject
to the rlimit.  Now that mediated devices are excluded when using
VFIO_UPDATE_VADDR, the amount of pinned memory equals the size of
the mapping.

Fixes: c3cbab24db38 ("vfio/type1: implement interfaces to update vaddr")

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 drivers/vfio/vfio_iommu_type1.c | 49 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index b04f485..e719c13 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -100,6 +100,7 @@ struct vfio_dma {
 	struct task_struct	*task;
 	struct rb_root		pfn_list;	/* Ex-user pinned pfn list */
 	unsigned long		*bitmap;
+	struct mm_struct	*mm;
 };
 
 struct vfio_batch {
@@ -424,6 +425,12 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
 	if (!mm)
 		return -ESRCH; /* process exited */
 
+	/* Avoid locked_vm underflow */
+	if (dma->mm != mm && npage < 0) {
+		mmput(mm);
+		return 0;
+	}
+
 	ret = mmap_write_lock_killable(mm);
 	if (!ret) {
 		ret = __account_locked_vm(mm, abs(npage), npage > 0, dma->task,
@@ -1180,6 +1187,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
 	vfio_unmap_unpin(iommu, dma, true);
 	vfio_unlink_dma(iommu, dma);
 	put_task_struct(dma->task);
+	mmdrop(dma->mm);
 	vfio_dma_bitmap_free(dma);
 	if (dma->vaddr_invalid) {
 		iommu->vaddr_invalid_count--;
@@ -1578,6 +1586,42 @@ static bool vfio_iommu_iova_dma_valid(struct vfio_iommu *iommu,
 	return list_empty(iova);
 }
 
+static int vfio_change_dma_owner(struct vfio_dma *dma)
+{
+	int ret = 0;
+	struct mm_struct *mm = get_task_mm(dma->task);
+
+	if (dma->mm != mm) {
+		long npage = dma->size >> PAGE_SHIFT;
+		bool new_lock_cap = capable(CAP_IPC_LOCK);
+		struct task_struct *new_task = current->group_leader;
+
+		ret = mmap_write_lock_killable(new_task->mm);
+		if (ret)
+			goto out;
+
+		ret = __account_locked_vm(new_task->mm, npage, true,
+					  new_task, new_lock_cap);
+		mmap_write_unlock(new_task->mm);
+		if (ret)
+			goto out;
+
+		if (dma->task != new_task) {
+			vfio_lock_acct(dma, -npage, 0);
+			put_task_struct(dma->task);
+			dma->task = get_task_struct(new_task);
+		}
+		mmdrop(dma->mm);
+		dma->mm = new_task->mm;
+		mmgrab(dma->mm);
+		dma->lock_cap = new_lock_cap;
+	}
+out:
+	if (mm)
+		mmput(mm);
+	return ret;
+}
+
 static int vfio_dma_do_map(struct vfio_iommu *iommu,
 			   struct vfio_iommu_type1_dma_map *map)
 {
@@ -1627,6 +1671,9 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
 			   dma->size != size) {
 			ret = -EINVAL;
 		} else {
+			ret = vfio_change_dma_owner(dma);
+			if (ret)
+				goto out_unlock;
 			dma->vaddr = vaddr;
 			dma->vaddr_invalid = false;
 			iommu->vaddr_invalid_count--;
@@ -1687,6 +1734,8 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
 	get_task_struct(current->group_leader);
 	dma->task = current->group_leader;
 	dma->lock_cap = capable(CAP_IPC_LOCK);
+	dma->mm = dma->task->mm;
+	mmgrab(dma->mm);
 
 	dma->pfn_list = RB_ROOT;
 
-- 
1.8.3.1

Re: [PATCH V3 2/5] vfio/type1: prevent locked_vm underflow

[Alex Williamson]

On Wed, 14 Dec 2022 11:22:48 -0800
Steve Sistare <steven.sistare@oracle.com> wrote:

> When a vfio container is preserved across exec using the VFIO_UPDATE_VADDR
> interfaces, locked_vm of the new mm becomes 0.  If the user later unmaps a
> dma mapping, locked_vm underflows to a large unsigned value, and a
> subsequent dma map request fails with ENOMEM in __account_locked_vm.
> 
> To avoid underflow, do not decrement locked_vm during unmap if the
> dma's mm has changed.  To restore the correct locked_vm count, when
> VFIO_DMA_MAP_FLAG_VADDR is used and the dma's mm has changed, add
> the mapping's pinned page count to the new mm->locked_vm, subject
> to the rlimit.  Now that mediated devices are excluded when using
> VFIO_UPDATE_VADDR, the amount of pinned memory equals the size of
> the mapping.
> 
> Fixes: c3cbab24db38 ("vfio/type1: implement interfaces to update vaddr")
> 
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 49 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index b04f485..e719c13 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -100,6 +100,7 @@ struct vfio_dma {
>  	struct task_struct	*task;
>  	struct rb_root		pfn_list;	/* Ex-user pinned pfn list */
>  	unsigned long		*bitmap;
> +	struct mm_struct	*mm;
>  };
>  
>  struct vfio_batch {
> @@ -424,6 +425,12 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
>  	if (!mm)
>  		return -ESRCH; /* process exited */
>  
> +	/* Avoid locked_vm underflow */
> +	if (dma->mm != mm && npage < 0) {
> +		mmput(mm);
> +		return 0;
> +	}

How about initialize ret = 0 and jump to the existing mmput() with a
goto, so there's no assumptions about whether we need the mmput() or
not.

> +
>  	ret = mmap_write_lock_killable(mm);
>  	if (!ret) {
>  		ret = __account_locked_vm(mm, abs(npage), npage > 0, dma->task,
> @@ -1180,6 +1187,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
>  	vfio_unmap_unpin(iommu, dma, true);
>  	vfio_unlink_dma(iommu, dma);
>  	put_task_struct(dma->task);
> +	mmdrop(dma->mm);
>  	vfio_dma_bitmap_free(dma);
>  	if (dma->vaddr_invalid) {
>  		iommu->vaddr_invalid_count--;
> @@ -1578,6 +1586,42 @@ static bool vfio_iommu_iova_dma_valid(struct vfio_iommu *iommu,
>  	return list_empty(iova);
>  }
>  
> +static int vfio_change_dma_owner(struct vfio_dma *dma)
> +{
> +	int ret = 0;
> +	struct mm_struct *mm = get_task_mm(dma->task);
> +
> +	if (dma->mm != mm) {
> +		long npage = dma->size >> PAGE_SHIFT;
> +		bool new_lock_cap = capable(CAP_IPC_LOCK);
> +		struct task_struct *new_task = current->group_leader;
> +
> +		ret = mmap_write_lock_killable(new_task->mm);
> +		if (ret)
> +			goto out;
> +
> +		ret = __account_locked_vm(new_task->mm, npage, true,
> +					  new_task, new_lock_cap);
> +		mmap_write_unlock(new_task->mm);
> +		if (ret)
> +			goto out;
> +
> +		if (dma->task != new_task) {
> +			vfio_lock_acct(dma, -npage, 0);
> +			put_task_struct(dma->task);
> +			dma->task = get_task_struct(new_task);
> +		}

IIUC, we're essentially open coding vfio_lock_acct() in the previous
section so that we can be sure we've accounted the new task before we
credit the previous task.  However, I was under the impression the task
remained the same, but the mm changes, which is how we end up with the
underflow described in the commit log.  What circumstances cause a task
change?  Thanks,

Alex


> +		mmdrop(dma->mm);
> +		dma->mm = new_task->mm;
> +		mmgrab(dma->mm);
> +		dma->lock_cap = new_lock_cap;
> +	}
> +out:
> +	if (mm)
> +		mmput(mm);
> +	return ret;
> +}
> +
>  static int vfio_dma_do_map(struct vfio_iommu *iommu,
>  			   struct vfio_iommu_type1_dma_map *map)
>  {
> @@ -1627,6 +1671,9 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>  			   dma->size != size) {
>  			ret = -EINVAL;
>  		} else {
> +			ret = vfio_change_dma_owner(dma);
> +			if (ret)
> +				goto out_unlock;
>  			dma->vaddr = vaddr;
>  			dma->vaddr_invalid = false;
>  			iommu->vaddr_invalid_count--;
> @@ -1687,6 +1734,8 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>  	get_task_struct(current->group_leader);
>  	dma->task = current->group_leader;
>  	dma->lock_cap = capable(CAP_IPC_LOCK);
> +	dma->mm = dma->task->mm;
> +	mmgrab(dma->mm);
>  
>  	dma->pfn_list = RB_ROOT;
>  

Re: [PATCH V3 2/5] vfio/type1: prevent locked_vm underflow

[Steven Sistare]

On 12/14/2022 3:03 PM, Alex Williamson wrote:
> On Wed, 14 Dec 2022 11:22:48 -0800
> Steve Sistare <steven.sistare@oracle.com> wrote:
> 
>> When a vfio container is preserved across exec using the VFIO_UPDATE_VADDR
>> interfaces, locked_vm of the new mm becomes 0.  If the user later unmaps a
>> dma mapping, locked_vm underflows to a large unsigned value, and a
>> subsequent dma map request fails with ENOMEM in __account_locked_vm.
>>
>> To avoid underflow, do not decrement locked_vm during unmap if the
>> dma's mm has changed.  To restore the correct locked_vm count, when
>> VFIO_DMA_MAP_FLAG_VADDR is used and the dma's mm has changed, add
>> the mapping's pinned page count to the new mm->locked_vm, subject
>> to the rlimit.  Now that mediated devices are excluded when using
>> VFIO_UPDATE_VADDR, the amount of pinned memory equals the size of
>> the mapping.
>>
>> Fixes: c3cbab24db38 ("vfio/type1: implement interfaces to update vaddr")
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 49 +++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 49 insertions(+)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index b04f485..e719c13 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -100,6 +100,7 @@ struct vfio_dma {
>>  	struct task_struct	*task;
>>  	struct rb_root		pfn_list;	/* Ex-user pinned pfn list */
>>  	unsigned long		*bitmap;
>> +	struct mm_struct	*mm;
>>  };
>>  
>>  struct vfio_batch {
>> @@ -424,6 +425,12 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
>>  	if (!mm)
>>  		return -ESRCH; /* process exited */
>>  
>> +	/* Avoid locked_vm underflow */
>> +	if (dma->mm != mm && npage < 0) {
>> +		mmput(mm);
>> +		return 0;
>> +	}
> 
> How about initialize ret = 0 and jump to the existing mmput() with a
> goto, so there's no assumptions about whether we need the mmput() or
> not.

OK.

>> +
>>  	ret = mmap_write_lock_killable(mm);
>>  	if (!ret) {
>>  		ret = __account_locked_vm(mm, abs(npage), npage > 0, dma->task,
>> @@ -1180,6 +1187,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
>>  	vfio_unmap_unpin(iommu, dma, true);
>>  	vfio_unlink_dma(iommu, dma);
>>  	put_task_struct(dma->task);
>> +	mmdrop(dma->mm);
>>  	vfio_dma_bitmap_free(dma);
>>  	if (dma->vaddr_invalid) {
>>  		iommu->vaddr_invalid_count--;
>> @@ -1578,6 +1586,42 @@ static bool vfio_iommu_iova_dma_valid(struct vfio_iommu *iommu,
>>  	return list_empty(iova);
>>  }
>>  
>> +static int vfio_change_dma_owner(struct vfio_dma *dma)
>> +{
>> +	int ret = 0;
>> +	struct mm_struct *mm = get_task_mm(dma->task);
>> +
>> +	if (dma->mm != mm) {
>> +		long npage = dma->size >> PAGE_SHIFT;
>> +		bool new_lock_cap = capable(CAP_IPC_LOCK);
>> +		struct task_struct *new_task = current->group_leader;
>> +
>> +		ret = mmap_write_lock_killable(new_task->mm);
>> +		if (ret)
>> +			goto out;
>> +
>> +		ret = __account_locked_vm(new_task->mm, npage, true,
>> +					  new_task, new_lock_cap);
>> +		mmap_write_unlock(new_task->mm);
>> +		if (ret)
>> +			goto out;
>> +
>> +		if (dma->task != new_task) {
>> +			vfio_lock_acct(dma, -npage, 0);
>> +			put_task_struct(dma->task);
>> +			dma->task = get_task_struct(new_task);
>> +		}
> 
> IIUC, we're essentially open coding vfio_lock_acct() in the previous
> section so that we can be sure we've accounted the new task before we
> credit the previous task.  

Correct.

> However, I was under the impression the task
> remained the same, but the mm changes, which is how we end up with the
> underflow described in the commit log.  What circumstances cause a task
> change?  Thanks,
The task changes if one does fork/exec live update.  I tested exec and fork/exec
with my changes.

- Steve

>> +		mmdrop(dma->mm);
>> +		dma->mm = new_task->mm;
>> +		mmgrab(dma->mm);
>> +		dma->lock_cap = new_lock_cap;
>> +	}
>> +out:
>> +	if (mm)
>> +		mmput(mm);
>> +	return ret;
>> +}
>> +
>>  static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>  			   struct vfio_iommu_type1_dma_map *map)
>>  {
>> @@ -1627,6 +1671,9 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>  			   dma->size != size) {
>>  			ret = -EINVAL;
>>  		} else {
>> +			ret = vfio_change_dma_owner(dma);
>> +			if (ret)
>> +				goto out_unlock;
>>  			dma->vaddr = vaddr;
>>  			dma->vaddr_invalid = false;
>>  			iommu->vaddr_invalid_count--;
>> @@ -1687,6 +1734,8 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>>  	get_task_struct(current->group_leader);
>>  	dma->task = current->group_leader;
>>  	dma->lock_cap = capable(CAP_IPC_LOCK);
>> +	dma->mm = dma->task->mm;
>> +	mmgrab(dma->mm);
>>  
>>  	dma->pfn_list = RB_ROOT;
>>  
> 

[PATCH V3 3/5] vfio/type1: revert "block on invalid vaddr"

[Steve Sistare]

Revert this dead code:
  commit 898b9eaeb3fe ("vfio/type1: block on invalid vaddr")

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 drivers/vfio/vfio_iommu_type1.c | 94 +++--------------------------------------
 1 file changed, 5 insertions(+), 89 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index e719c13..6523b7d 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -72,7 +72,6 @@ struct vfio_iommu {
 	unsigned int		vaddr_invalid_count;
 	uint64_t		pgsize_bitmap;
 	uint64_t		num_non_pinned_groups;
-	wait_queue_head_t	vaddr_wait;
 	bool			v2;
 	bool			nesting;
 	bool			dirty_page_tracking;
@@ -153,8 +152,6 @@ struct vfio_regions {
 #define DIRTY_BITMAP_PAGES_MAX	 ((u64)INT_MAX)
 #define DIRTY_BITMAP_SIZE_MAX	 DIRTY_BITMAP_BYTES(DIRTY_BITMAP_PAGES_MAX)
 
-#define WAITED 1
-
 static int put_pfn(unsigned long pfn, int prot);
 
 static struct vfio_iommu_group*
@@ -602,61 +599,6 @@ static int vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
 	return ret;
 }
 
-static int vfio_wait(struct vfio_iommu *iommu)
-{
-	DEFINE_WAIT(wait);
-
-	prepare_to_wait(&iommu->vaddr_wait, &wait, TASK_KILLABLE);
-	mutex_unlock(&iommu->lock);
-	schedule();
-	mutex_lock(&iommu->lock);
-	finish_wait(&iommu->vaddr_wait, &wait);
-	if (kthread_should_stop() || !iommu->container_open ||
-	    fatal_signal_pending(current)) {
-		return -EFAULT;
-	}
-	return WAITED;
-}
-
-/*
- * Find dma struct and wait for its vaddr to be valid.  iommu lock is dropped
- * if the task waits, but is re-locked on return.  Return result in *dma_p.
- * Return 0 on success with no waiting, WAITED on success if waited, and -errno
- * on error.
- */
-static int vfio_find_dma_valid(struct vfio_iommu *iommu, dma_addr_t start,
-			       size_t size, struct vfio_dma **dma_p)
-{
-	int ret = 0;
-
-	do {
-		*dma_p = vfio_find_dma(iommu, start, size);
-		if (!*dma_p)
-			return -EINVAL;
-		else if (!(*dma_p)->vaddr_invalid)
-			return ret;
-		else
-			ret = vfio_wait(iommu);
-	} while (ret == WAITED);
-
-	return ret;
-}
-
-/*
- * Wait for all vaddr in the dma_list to become valid.  iommu lock is dropped
- * if the task waits, but is re-locked on return.  Return 0 on success with no
- * waiting, WAITED on success if waited, and -errno on error.
- */
-static int vfio_wait_all_valid(struct vfio_iommu *iommu)
-{
-	int ret = 0;
-
-	while (iommu->vaddr_invalid_count && ret >= 0)
-		ret = vfio_wait(iommu);
-
-	return ret;
-}
-
 /*
  * Attempt to pin pages.  We really don't want to track all the pfns and
  * the iommu can only map chunks of consecutive pfns anyway, so get the
@@ -857,7 +799,6 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
 	unsigned long remote_vaddr;
 	struct vfio_dma *dma;
 	bool do_accounting;
-	dma_addr_t iova;
 
 	if (!iommu || !pages)
 		return -EINVAL;
@@ -874,22 +815,6 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
 		goto pin_done;
 	}
 
-	/*
-	 * Wait for all necessary vaddr's to be valid so they can be used in
-	 * the main loop without dropping the lock, to avoid racing vs unmap.
-	 */
-again:
-	if (iommu->vaddr_invalid_count) {
-		for (i = 0; i < npage; i++) {
-			iova = user_iova + PAGE_SIZE * i;
-			ret = vfio_find_dma_valid(iommu, iova, PAGE_SIZE, &dma);
-			if (ret < 0)
-				goto pin_done;
-			if (ret == WAITED)
-				goto again;
-		}
-	}
-
 	/* Fail if no dma_umap notifier is registered */
 	if (list_empty(&iommu->device_list)) {
 		ret = -EINVAL;
@@ -905,6 +830,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
 
 	for (i = 0; i < npage; i++) {
 		unsigned long phys_pfn;
+		dma_addr_t iova;
 		struct vfio_pfn *vpfn;
 
 		iova = user_iova + PAGE_SIZE * i;
@@ -1189,10 +1115,8 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
 	put_task_struct(dma->task);
 	mmdrop(dma->mm);
 	vfio_dma_bitmap_free(dma);
-	if (dma->vaddr_invalid) {
+	if (dma->vaddr_invalid)
 		iommu->vaddr_invalid_count--;
-		wake_up_all(&iommu->vaddr_wait);
-	}
 	kfree(dma);
 	iommu->dma_avail++;
 }
@@ -1677,7 +1601,6 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
 			dma->vaddr = vaddr;
 			dma->vaddr_invalid = false;
 			iommu->vaddr_invalid_count--;
-			wake_up_all(&iommu->vaddr_wait);
 		}
 		goto out_unlock;
 	} else if (dma) {
@@ -1768,10 +1691,6 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
 	unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
 	int ret;
 
-	ret = vfio_wait_all_valid(iommu);
-	if (ret < 0)
-		return ret;
-
 	/* Arbitrarily pick the first domain in the list for lookups */
 	if (!list_empty(&iommu->domain_list))
 		d = list_first_entry(&iommu->domain_list,
@@ -2662,7 +2581,6 @@ static void *vfio_iommu_type1_open(unsigned long arg)
 	mutex_init(&iommu->lock);
 	mutex_init(&iommu->device_list_lock);
 	INIT_LIST_HEAD(&iommu->device_list);
-	init_waitqueue_head(&iommu->vaddr_wait);
 	iommu->pgsize_bitmap = PAGE_MASK;
 	INIT_LIST_HEAD(&iommu->emulated_iommu_groups);
 
@@ -3159,7 +3077,6 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
 	struct vfio_dma *dma;
 	bool kthread = current->mm == NULL;
 	size_t offset;
-	int ret;
 
 	if (iommu->vaddr_invalid_count) {
 		WARN_ONCE(1, "mdev not allowed with VFIO_UPDATE_VADDR\n");
@@ -3168,9 +3085,9 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
 
 	*copied = 0;
 
-	ret = vfio_find_dma_valid(iommu, user_iova, 1, &dma);
-	if (ret < 0)
-		return ret;
+	dma = vfio_find_dma(iommu, user_iova, 1);
+	if (!dma)
+		return -EINVAL;
 
 	if ((write && !(dma->prot & IOMMU_WRITE)) ||
 			!(dma->prot & IOMMU_READ))
@@ -3272,7 +3189,6 @@ static void vfio_iommu_type1_notify(void *iommu_data,
 	mutex_lock(&iommu->lock);
 	iommu->container_open = false;
 	mutex_unlock(&iommu->lock);
-	wake_up_all(&iommu->vaddr_wait);
 }
 
 static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
-- 
1.8.3.1

[PATCH V3 4/5] vfio/type1: revert "implement notify callback"

[Steve Sistare]

This is dead code.  Revert it.
  commit 487ace134053 ("vfio/type1: implement notify callback")

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 drivers/vfio/vfio_iommu_type1.c | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 6523b7d..2d602be 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -75,7 +75,6 @@ struct vfio_iommu {
 	bool			v2;
 	bool			nesting;
 	bool			dirty_page_tracking;
-	bool			container_open;
 	struct list_head	emulated_iommu_groups;
 };
 
@@ -2577,7 +2576,6 @@ static void *vfio_iommu_type1_open(unsigned long arg)
 	INIT_LIST_HEAD(&iommu->iova_list);
 	iommu->dma_list = RB_ROOT;
 	iommu->dma_avail = dma_entry_limit;
-	iommu->container_open = true;
 	mutex_init(&iommu->lock);
 	mutex_init(&iommu->device_list_lock);
 	INIT_LIST_HEAD(&iommu->device_list);
@@ -3179,18 +3177,6 @@ static int vfio_iommu_type1_dma_rw(void *iommu_data, dma_addr_t user_iova,
 	return domain;
 }
 
-static void vfio_iommu_type1_notify(void *iommu_data,
-				    enum vfio_iommu_notify_type event)
-{
-	struct vfio_iommu *iommu = iommu_data;
-
-	if (event != VFIO_IOMMU_CONTAINER_CLOSE)
-		return;
-	mutex_lock(&iommu->lock);
-	iommu->container_open = false;
-	mutex_unlock(&iommu->lock);
-}
-
 static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
 	.name			= "vfio-iommu-type1",
 	.owner			= THIS_MODULE,
@@ -3205,7 +3191,6 @@ static void vfio_iommu_type1_notify(void *iommu_data,
 	.unregister_device	= vfio_iommu_type1_unregister_device,
 	.dma_rw			= vfio_iommu_type1_dma_rw,
 	.group_iommu_domain	= vfio_iommu_type1_group_iommu_domain,
-	.notify			= vfio_iommu_type1_notify,
 };
 
 static int __init vfio_iommu_type1_init(void)
-- 
1.8.3.1

[PATCH V3 5/5] vfio: revert "iommu driver notify callback"

[Steve Sistare]

Revert this dead code:
  commit ec5e32940cc9 ("vfio: iommu driver notify callback")

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 drivers/vfio/container.c | 5 -----
 drivers/vfio/vfio.h      | 7 -------
 2 files changed, 12 deletions(-)

diff --git a/drivers/vfio/container.c b/drivers/vfio/container.c
index d74164a..5bfd10d 100644
--- a/drivers/vfio/container.c
+++ b/drivers/vfio/container.c
@@ -382,11 +382,6 @@ static int vfio_fops_open(struct inode *inode, struct file *filep)
 static int vfio_fops_release(struct inode *inode, struct file *filep)
 {
 	struct vfio_container *container = filep->private_data;
-	struct vfio_iommu_driver *driver = container->iommu_driver;
-
-	if (driver && driver->ops->notify)
-		driver->ops->notify(container->iommu_data,
-				    VFIO_IOMMU_CONTAINER_CLOSE);
 
 	filep->private_data = NULL;
 
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
index bcad54b..8a439c6 100644
--- a/drivers/vfio/vfio.h
+++ b/drivers/vfio/vfio.h
@@ -62,11 +62,6 @@ struct vfio_group {
 	struct blocking_notifier_head	notifier;
 };
 
-/* events for the backend driver notify callback */
-enum vfio_iommu_notify_type {
-	VFIO_IOMMU_CONTAINER_CLOSE = 0,
-};
-
 /**
  * struct vfio_iommu_driver_ops - VFIO IOMMU driver callbacks
  */
@@ -97,8 +92,6 @@ struct vfio_iommu_driver_ops {
 				  void *data, size_t count, bool write);
 	struct iommu_domain *(*group_iommu_domain)(void *iommu_data,
 						   struct iommu_group *group);
-	void		(*notify)(void *iommu_data,
-				  enum vfio_iommu_notify_type event);
 };
 
 struct vfio_iommu_driver {
-- 
1.8.3.1