diff mbox series

[v1,5/8] iommufd: Add replace support in iommufd_access_set_ioas()

Message ID bfe5aed6d354ef547979f0b256c8a3f9bd5b223b.1675320212.git.nicolinc@nvidia.com
State New
Headers
Series Add IO page table replacement support |

Commit Message

Nicolin Chen Feb. 2, 2023, 7:05 a.m. UTC 
  Support an access->ioas replacement in iommufd_access_set_ioas(), which
sets the access->ioas to NULL provisionally so that any further incoming
iommufd_access_pin_pages() callback can be blocked.

Then, call access->ops->unmap() to clean up the entire iopt. To allow an
iommufd_access_unpin_pages() callback to happen via this unmap() call,
add an ioas_unpin pointer so the unpin routine won't be affected by the
"access->ioas = NULL" trick above.

Also, a vdev without an ops->dma_unmap implementation cannot replace its
access->ioas pointer. So add an iommufd_access_ioas_is_attached() helper
to sanity that.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 drivers/iommu/iommufd/device.c          | 28 +++++++++++++++++++++++--
 drivers/iommu/iommufd/iommufd_private.h |  1 +
 drivers/vfio/iommufd.c                  |  4 ++++
 include/linux/iommufd.h                 |  1 +
 4 files changed, 32 insertions(+), 2 deletions(-)

Comments

Tian, Kevin Feb. 3, 2023, 10:10 a.m. UTC | #1 
> From: Nicolin Chen <nicolinc@nvidia.com>
> Sent: Thursday, February 2, 2023 3:05 PM
> 
> Support an access->ioas replacement in iommufd_access_set_ioas(), which
> sets the access->ioas to NULL provisionally so that any further incoming
> iommufd_access_pin_pages() callback can be blocked.
> 
> Then, call access->ops->unmap() to clean up the entire iopt. To allow an
> iommufd_access_unpin_pages() callback to happen via this unmap() call,
> add an ioas_unpin pointer so the unpin routine won't be affected by the
> "access->ioas = NULL" trick above.
> 
> Also, a vdev without an ops->dma_unmap implementation cannot replace its
> access->ioas pointer. So add an iommufd_access_ioas_is_attached() helper
> to sanity that.
> 

Presumably a driver which doesn't implement ops->dma_unmap shouldn't
be allowed to do pin/unpin. But it could use vfio_dma_rw() to access an
iova range. In the latter case I don't see why replace cannot work.

Probably what's required here is to deny !ops->dma_unmap in
vfio_pin/unpin_pages then making here replace always allowed?
Jason Gunthorpe Feb. 3, 2023, 12:31 p.m. UTC | #2 
On Fri, Feb 03, 2023 at 10:10:45AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: Thursday, February 2, 2023 3:05 PM
> > 
> > Support an access->ioas replacement in iommufd_access_set_ioas(), which
> > sets the access->ioas to NULL provisionally so that any further incoming
> > iommufd_access_pin_pages() callback can be blocked.
> > 
> > Then, call access->ops->unmap() to clean up the entire iopt. To allow an
> > iommufd_access_unpin_pages() callback to happen via this unmap() call,
> > add an ioas_unpin pointer so the unpin routine won't be affected by the
> > "access->ioas = NULL" trick above.
> > 
> > Also, a vdev without an ops->dma_unmap implementation cannot replace its
> > access->ioas pointer. So add an iommufd_access_ioas_is_attached() helper
> > to sanity that.
> > 
> 
> Presumably a driver which doesn't implement ops->dma_unmap shouldn't
> be allowed to do pin/unpin. But it could use vfio_dma_rw() to access an
> iova range. In the latter case I don't see why replace cannot work.
> 
> Probably what's required here is to deny !ops->dma_unmap in
> vfio_pin/unpin_pages then making here replace always allowed?

That makes sense

Jason
Nicolin Chen Feb. 3, 2023, 10:25 p.m. UTC | #3 
On Fri, Feb 03, 2023 at 08:31:52AM -0400, Jason Gunthorpe wrote:
> On Fri, Feb 03, 2023 at 10:10:45AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > Sent: Thursday, February 2, 2023 3:05 PM
> > > 
> > > Support an access->ioas replacement in iommufd_access_set_ioas(), which
> > > sets the access->ioas to NULL provisionally so that any further incoming
> > > iommufd_access_pin_pages() callback can be blocked.
> > > 
> > > Then, call access->ops->unmap() to clean up the entire iopt. To allow an
> > > iommufd_access_unpin_pages() callback to happen via this unmap() call,
> > > add an ioas_unpin pointer so the unpin routine won't be affected by the
> > > "access->ioas = NULL" trick above.
> > > 
> > > Also, a vdev without an ops->dma_unmap implementation cannot replace its
> > > access->ioas pointer. So add an iommufd_access_ioas_is_attached() helper
> > > to sanity that.
> > > 
> > 
> > Presumably a driver which doesn't implement ops->dma_unmap shouldn't
> > be allowed to do pin/unpin. But it could use vfio_dma_rw() to access an
> > iova range. In the latter case I don't see why replace cannot work.
> > 
> > Probably what's required here is to deny !ops->dma_unmap in
> > vfio_pin/unpin_pages then making here replace always allowed?
> 
> That makes sense

Will change that in v2.

Thanks
Nic
diff mbox series

Patch

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index f4bd6f532a90..8118d5262800 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -509,11 +509,23 @@  int iommufd_access_set_ioas(struct iommufd_access *access, u32 ioas_id)
 		iommufd_ref_to_users(obj);
 	}
 
+	/*
+	 * Set ioas to NULL to block any further iommufd_access_pin_pages().
+	 * iommufd_access_unpin_pages() can continue using access->ioas_unpin.
+	 */
+	access->ioas = NULL;
+
 	if (cur_ioas) {
+		if (new_ioas) {
+			mutex_unlock(&access->ioas_lock);
+			access->ops->unmap(access->data, 0, ULONG_MAX);
+			mutex_lock(&access->ioas_lock);
+		}
 		iopt_remove_access(&cur_ioas->iopt, access);
 		refcount_dec(&cur_ioas->obj.users);
 	}
 
+	access->ioas_unpin = new_ioas;
 	access->ioas = new_ioas;
 	mutex_unlock(&access->ioas_lock);
 
@@ -527,6 +539,18 @@  int iommufd_access_set_ioas(struct iommufd_access *access, u32 ioas_id)
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_access_set_ioas, IOMMUFD);
 
+bool iommufd_access_ioas_is_attached(struct iommufd_access *access)
+{
+	bool attached;
+
+	mutex_lock(&access->ioas_lock);
+	attached = !!access->ioas;
+	mutex_unlock(&access->ioas_lock);
+
+	return attached;
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_access_ioas_is_attached, IOMMUFD);
+
 /**
  * iommufd_access_notify_unmap - Notify users of an iopt to stop using it
  * @iopt: iopt to work on
@@ -587,11 +611,11 @@  void iommufd_access_unpin_pages(struct iommufd_access *access,
 		return;
 
 	mutex_lock(&access->ioas_lock);
-	if (!access->ioas) {
+	if (!access->ioas_unpin) {
 		mutex_unlock(&access->ioas_lock);
 		return;
 	}
-	iopt = &access->ioas->iopt;
+	iopt = &access->ioas_unpin->iopt;
 
 	down_read(&iopt->iova_rwsem);
 	iopt_for_each_contig_area(&iter, area, iopt, iova, last_iova)
diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 2f4bb106bac6..593138bb37b8 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -261,6 +261,7 @@  struct iommufd_access {
 	struct iommufd_object obj;
 	struct iommufd_ctx *ictx;
 	struct iommufd_ioas *ioas;
+	struct iommufd_ioas *ioas_unpin;
 	struct mutex ioas_lock;
 	const struct iommufd_access_ops *ops;
 	void *data;
diff --git a/drivers/vfio/iommufd.c b/drivers/vfio/iommufd.c
index 78a8e4641cbf..7e09defbcffe 100644
--- a/drivers/vfio/iommufd.c
+++ b/drivers/vfio/iommufd.c
@@ -187,6 +187,10 @@  int vfio_iommufd_emulated_attach_ioas(struct vfio_device *vdev, u32 *pt_id)
 	if (!vdev->iommufd_access)
 		return -ENOENT;
 
+	if (!vdev->ops->dma_unmap && pt_id &&
+	    iommufd_access_ioas_is_attached(vdev->iommufd_access))
+		return -EBUSY;
+
 	iommufd_access_set_ioas(vdev->iommufd_access, *pt_id);
 	return 0;
 }
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 0e30f2ce27cd..e8d764b2c14c 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -44,6 +44,7 @@  iommufd_access_create(struct iommufd_ctx *ictx,
 		      const struct iommufd_access_ops *ops, void *data);
 void iommufd_access_destroy(struct iommufd_access *access);
 int iommufd_access_set_ioas(struct iommufd_access *access, u32 ioas_id);
+bool iommufd_access_ioas_is_attached(struct iommufd_access *access);
 
 void iommufd_ctx_get(struct iommufd_ctx *ictx);