From: Robin Murphy <robin.murphy@arm.com>
Date: Thu, 21 Sep 2017 16:52:46 +0100
Subject: iommu/iova: Add rbtree anchor node
Git-commit: bb68b2fbfbd643d4407541f9c7a16a2c9b3a57c7
Patch-mainline: v4.15-rc1
References: fate#326252

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.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
---
 drivers/iommu/iova.c |   15 +++++++++++++--
 include/linux/iova.h |    1 +
 2 files changed, 14 insertions(+), 2 deletions(-)

--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -23,6 +23,9 @@
 #include <linux/smp.h>
 #include <linux/bitops.h>
 
+/* The anchor node sits above the top of the usable address space */
+#define IOVA_ANCHOR	~0UL
+
 static bool iova_rcache_insert(struct iova_domain *iovad,
 			       unsigned long pfn,
 			       unsigned long size);
@@ -54,6 +57,9 @@ init_iova_domain(struct iova_domain *iov
 	iovad->dma_32bit_pfn = 1UL << (32 - iova_shift(iovad));
 	iovad->flush_cb = NULL;
 	iovad->fq = NULL;
+	iovad->anchor.pfn_lo = iovad->anchor.pfn_hi = IOVA_ANCHOR;
+	rb_link_node(&iovad->anchor.node, NULL, &iovad->rbroot.rb_node);
+	rb_insert_color(&iovad->anchor.node, &iovad->rbroot);
 	init_iova_rcaches(iovad);
 }
 EXPORT_SYMBOL_GPL(init_iova_domain);
@@ -118,7 +124,7 @@ __get_cached_rbnode(struct iova_domain *
 	if (!cached_node)
 		cached_node = iovad->cached_node;
 	if (!cached_node)
-		return rb_last(&iovad->rbroot);
+		return rb_prev(&iovad->anchor.node);
 
 	curr_iova = rb_entry(cached_node, struct iova, node);
 	*limit_pfn = min(*limit_pfn, curr_iova->pfn_lo);
@@ -241,7 +247,8 @@ EXPORT_SYMBOL(alloc_iova_mem);
 
 void free_iova_mem(struct iova *iova)
 {
-	kmem_cache_free(iova_cache, iova);
+	if (iova->pfn_lo != IOVA_ANCHOR)
+		kmem_cache_free(iova_cache, iova);
 }
 EXPORT_SYMBOL(free_iova_mem);
 
@@ -677,6 +684,10 @@ reserve_iova(struct iova_domain *iovad,
 	struct iova *iova;
 	unsigned int overlap = 0;
 
+	/* Don't allow nonsensical pfns */
+	if (WARN_ON((pfn_hi | pfn_lo) > (ULLONG_MAX >> iova_shift(iovad))))
+		return NULL;
+
 	spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);
 	for (node = rb_first(&iovad->rbroot); node; node = rb_next(node)) {
 		if (__is_range_overlap(node, pfn_lo, pfn_hi)) {
--- a/include/linux/iova.h
+++ b/include/linux/iova.h
@@ -75,6 +75,7 @@ struct iova_domain {
 	unsigned long	granule;	/* pfn granularity for this domain */
 	unsigned long	start_pfn;	/* Lower limit for this domain */
 	unsigned long	dma_32bit_pfn;
+	struct iova	anchor;		/* rbtree lookup anchor */
 	struct iova_rcache rcaches[IOVA_RANGE_CACHE_MAX_SIZE];	/* IOVA range caches */
 
 	iova_flush_cb	flush_cb;	/* Call-Back function to flush IOMMU