On 8/12/25 06:59, Nicolin Chen wrote:
There is a need to attach a PCI device that's under a reset to temporally
the blocked domain (i.e. detach it from its previously attached domain),
and then to reattach it back to its previous domain (i.e. detach it from
the blocked domain) after reset.
During the reset stage, there can be races from other attach/detachment.
To solve this, a per-gdev reset flag will be introduced so that all the
attach functions will bypass the driver-level attach_dev callbacks, but
only update the group->domain pointer. The reset recovery procedure will
attach directly to the cached pointer so things will be back to normal.
On the other hand, the iommu_get_domain_for_dev() API always returns the
group->domain pointer, and several IOMMMU drivers call this API in their
attach_dev callback functions to get the currently attached domain for a
device, which will be broken for the recovery case mentioned above:
1. core asks the driver to attach dev from blocked to group->domain
2. driver attaches dev from group->domain to group->domain
So, iommu_get_domain_for_dev() should check the gdev flag and return the
blocked domain if the flag is set. But the caller of this API could hold
the group->mutex already or not, making it difficult to add the lock.
Introduce a new iommu_get_domain_for_dev_locked() helper to be used by
those drivers in a context that is already under the protection of the
group->mutex, e.g. those attach_dev callback functions. And roll out the
new helper to all the existing IOMMU drivers.
Given that iommu_group->mutex is transparent to the iommu driver, how
about
/*
* Called only by iommu drivers in the callback context where
* group->mutex has already been held by the core.
*/
struct iommu_domain *iommu_get_domain_for_dev_internal(struct device *dev)
{
...
lockdep_assert_held(&group->mutex);
...
}
?
Add a lockdep_assert_not_held to the existing iommu_get_domain_for_dev()
to note that it would be only used outside the group->mutex.
Signed-off-by: Nicolin Chen<nicolinc@xxxxxxxxxx>
Thanks,
baolu
