[PATCH v5 5/6] iommu/iova: Add rbtree anchor node

Add a permanent dummy IOVA reservation to the rbtree, such that we can always access the top of the address space instantly. The immediate benefit is that we remove the overhead of the rb_last() traversal when not using the cached node, but it also paves the way for further simplifications.

[PATCH v5 5/6] iommu/iova: Add rbtree anchor node

Add a permanent dummy IOVA reservation to the rbtree, such that we can always access the top of the address space instantly. The immediate benefit is that we remove the overhead of the rb_last() traversal when not using the cached node, but it also paves the way for further simplifications.