On 6/5/24 4:15 PM, Tian, Kevin wrote:
From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
Sent: Monday, May 27, 2024 12:05 PM
@@ -69,11 +68,16 @@ static struct iommu_mm_data
*iommu_alloc_mm_data(struct mm_struct *mm, struct de
*/
struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct
mm_struct *mm)
{
+ struct iommu_group *group = dev->iommu_group;
+ struct iommu_attach_handle *attach_handle;
struct iommu_mm_data *iommu_mm;
struct iommu_domain *domain;
struct iommu_sva *handle;
it's confusing to have both 'handle' and 'attach_handle' in one function.
Clearer to rename 'handle' as 'sva'.
Yes. Could be cleaned up in a separated patch. All sva handle in
iommu-sva.c should be converted if we decide to do that.
int ret;
+ if (!group)
+ return ERR_PTR(-ENODEV);
+
mutex_lock(&iommu_sva_lock);
/* Allocate mm->pasid if necessary. */
@@ -83,12 +87,13 @@ struct iommu_sva *iommu_sva_bind_device(struct
device *dev, struct mm_struct *mm
goto out_unlock;
}
- list_for_each_entry(handle, &mm->iommu_mm->sva_handles,
handle_item) {
- if (handle->dev == dev) {
- refcount_inc(&handle->users);
- mutex_unlock(&iommu_sva_lock);
- return handle;
- }
+ /* A bond already exists, just take a reference`. */
+ attach_handle = iommu_attach_handle_get(group, iommu_mm-
pasid, IOMMU_DOMAIN_SVA);
+ if (!IS_ERR(attach_handle)) {
+ handle = container_of(attach_handle, struct iommu_sva,
handle);
+ refcount_inc(&handle->users);
+ mutex_unlock(&iommu_sva_lock);
+ return handle;
}
It's counter-intuitive to move forward when an error is returned.
e.g. if it's -EBUSY indicating the pasid already used for another type then
following attempts shouldn't been tried.
probably we should have iommu_attach_handle_get() return NULL
instead of -ENOENT when the entry is free? then:
attach_handle = iommu_attach_handle_get();
if (IS_ERR(attach_handle)) {
ret = PTR_ERR(attach_handle);
goto out_unlock;
} else if (attach_handle) {
/* matched and increase handle->users */
}
/* free entry falls through */
But then there is one potential issue with the design that 'handle'
can be optional in iommu_attach_device_pasid(). In that case
xa_load returns NULL then we cannot differentiate a real unused
PASID vs. one which has been attached w/o an handle.
The PASID should be allocated exclusively. This means that once a PASID
is assigned to A, it shouldn't be assigned to B at the same time. If a
single PASID is used for multiple purposes, it's likely a bug in the
system.
So the logic of iommu_attach_handle_get() here is: has an SVA domain
already been installed for this PASID? If so, just reuse it. Otherwise,
try to install a new SVA domain.
Does it suggest that having the caller to always provide a handle
makes more sense?
I'm neutral on this since only sva bind and iopf path delivery currently
require an attach handle.
Best regards,
baolu