Hi Christoph,
On 2021/11/15 21:27, Christoph Hellwig wrote:
On Mon, Nov 15, 2021 at 10:05:47AM +0800, Lu Baolu wrote:
The vfio needs to set DMA_OWNER_USER for the entire group when attaching
The vfio subsystem? driver?
"vfio subsystem"
it to a vfio container. So expose group variants of setting/releasing dma
ownership for this purpose.
This also exposes the helper iommu_group_dma_owner_unclaimed() for vfio
report to userspace if the group is viable to user assignment, for
.. for vfio to report .. ?
Yes.
void iommu_device_release_dma_owner(struct device *dev, enum iommu_dma_owner owner);
+int iommu_group_set_dma_owner(struct iommu_group *group, enum iommu_dma_owner owner,
+ struct file *user_file);
+void iommu_group_release_dma_owner(struct iommu_group *group, enum iommu_dma_owner owner);
Pleae avoid all these overly long lines.
Sure. Thanks!
+static inline int iommu_group_set_dma_owner(struct iommu_group *group,
+ enum iommu_dma_owner owner,
+ struct file *user_file)
+{
+ return -EINVAL;
+}
+
+static inline void iommu_group_release_dma_owner(struct iommu_group *group,
+ enum iommu_dma_owner owner)
+{
+}
+
+static inline bool iommu_group_dma_owner_unclaimed(struct iommu_group *group)
+{
+ return false;
+}
Why do we need these stubs? All potential callers should already
require CONFIG_IOMMU_API? Same for the helpers added in patch 1, btw.
You are right. This helper is only for vfio which requires IOMMU_API. I
will remove this.
The helpers in patch 1 seem not the same. The driver core (or bus
dma_configure() callback as suggested) will also call them.
+ mutex_lock(&group->mutex);
+ ret = __iommu_group_set_dma_owner(group, owner, user_file);
+ mutex_unlock(&group->mutex);
+ mutex_lock(&group->mutex);
+ __iommu_group_release_dma_owner(group, owner);
+ mutex_unlock(&group->mutex);
Unless I'm missing something (just skipping over the patches),
the existing callers also take the lock just around these calls,
so we don't really need the __-prefixed lowlevel helpers.
Move mutex_lock/unlock will make the helper implementation easier. :-)
It seems to be common code style in iommu core. For example,
__iommu_attach_group(), __iommu_group_for_each_dev(), etc.
+ mutex_lock(&group->mutex);
+ owner = group->dma_owner;
+ mutex_unlock(&group->mutex);
No need for a lock to read a single scalar.
Adding the lock will make kcasn happy. Jason G also told me that
[citing from his review comment]
"
It is always incorrect to read concurrent data without an annotation
of some kind.
For instance it can cause mis-execution of logic where the compiler is
unaware that a value it loads is allowed to change - ie no
READ_ONCE/WRITE_ONCE semantic.
"
+
+ return owner == DMA_OWNER_NONE;
+}
+EXPORT_SYMBOL_GPL(iommu_group_dma_owner_unclaimed);
Best regards,
baolu
