dmar: reserve memory windows of PCIe root port

PCI memory address space is shared between memory-mapped devices (MMIO)
and host memory (which may be remapped by an IOMMU). Device accesses to
an address within a memory aperture in a PCIe root port will be treated
as peer-to-peer and not forwarded to an IOMMU. To avoid this, reserve
the address space of the root port's memory apertures in the address
space used by the IOMMU for remapping.

Reviewed by:	kib, tychon
Discussed with:	Anton Rang <rang@acm.org>
Tested by:	tychon
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D27503

2 files changed, 69 insertions, 5 deletions

diff --git a/sys/dev/iommu/iommu.h b/sys/dev/iommu/iommu.h
index 388a8cb3b2ce..ba592ea08ff1 100644
--- a/sys/dev/iommu/iommu.h
+++ b/sys/dev/iommu/iommu.h
@@ -199,6 +199,8 @@ int iommu_gas_map_region(struct iommu_domain *domain,
     struct iommu_map_entry *entry, u_int eflags, u_int flags, vm_page_t *ma);
 int iommu_gas_reserve_region(struct iommu_domain *domain, iommu_gaddr_t start,
     iommu_gaddr_t end, struct iommu_map_entry **entry0);
+int iommu_gas_reserve_region_extend(struct iommu_domain *domain,
+    iommu_gaddr_t start, iommu_gaddr_t end);
 
 void iommu_set_buswide_ctx(struct iommu_unit *unit, u_int busno);
 bool iommu_is_buswide_ctx(struct iommu_unit *unit, u_int busno);
diff --git a/sys/dev/iommu/iommu_gas.c b/sys/dev/iommu/iommu_gas.c
index 841bb3c83da5..431c0c195c35 100644
--- a/sys/dev/iommu/iommu_gas.c
+++ b/sys/dev/iommu/iommu_gas.c
@@ -677,6 +677,22 @@ iommu_gas_map_region(struct iommu_domain *domain, struct iommu_map_entry *entry,
 	return (0);
 }
 
+static int
+iommu_gas_reserve_region_locked(struct iommu_domain *domain,
+    iommu_gaddr_t start, iommu_gaddr_t end, struct iommu_map_entry *entry)
+{
+	int error;
+
+	IOMMU_DOMAIN_ASSERT_LOCKED(domain);
+
+	entry->start = start;
+	entry->end = end;
+	error = iommu_gas_alloc_region(domain, entry, IOMMU_MF_CANWAIT);
+	if (error == 0)
+		entry->flags |= IOMMU_MAP_ENTRY_UNMAPPED;
+	return (error);
+}
+
 int
 iommu_gas_reserve_region(struct iommu_domain *domain, iommu_gaddr_t start,
     iommu_gaddr_t end, struct iommu_map_entry **entry0)
@@ -685,12 +701,8 @@ iommu_gas_reserve_region(struct iommu_domain *domain, iommu_gaddr_t start,
 	int error;
 
 	entry = iommu_gas_alloc_entry(domain, IOMMU_PGF_WAITOK);
-	entry->start = start;
-	entry->end = end;
 	IOMMU_DOMAIN_LOCK(domain);
-	error = iommu_gas_alloc_region(domain, entry, IOMMU_MF_CANWAIT);
-	if (error == 0)
-		entry->flags |= IOMMU_MAP_ENTRY_UNMAPPED;
+	error = iommu_gas_reserve_region_locked(domain, start, end, entry);
 	IOMMU_DOMAIN_UNLOCK(domain);
 	if (error != 0)
 		iommu_gas_free_entry(domain, entry);
@@ -699,6 +711,56 @@ iommu_gas_reserve_region(struct iommu_domain *domain, iommu_gaddr_t start,
 	return (error);
 }
 
+/*
+ * As in iommu_gas_reserve_region, reserve [start, end), but allow for existing
+ * entries.
+ */
+int
+iommu_gas_reserve_region_extend(struct iommu_domain *domain,
+    iommu_gaddr_t start, iommu_gaddr_t end)
+{
+	struct iommu_map_entry *entry, *next, *prev, key = {};
+	iommu_gaddr_t entry_start, entry_end;
+	int error;
+
+	error = 0;
+	entry = NULL;
+	end = ummin(end, domain->end);
+	while (start < end) {
+		/* Preallocate an entry. */
+		if (entry == NULL)
+			entry = iommu_gas_alloc_entry(domain,
+			    IOMMU_PGF_WAITOK);
+		/* Calculate the free region from here to the next entry. */
+		key.start = key.end = start;
+		IOMMU_DOMAIN_LOCK(domain);
+		next = RB_NFIND(iommu_gas_entries_tree, &domain->rb_root, &key);
+		KASSERT(next != NULL, ("domain %p with end %#jx has no entry "
+		    "after %#jx", domain, (uintmax_t)domain->end,
+		    (uintmax_t)start));
+		entry_end = ummin(end, next->start);
+		prev = RB_PREV(iommu_gas_entries_tree, &domain->rb_root, next);
+		if (prev != NULL)
+			entry_start = ummax(start, prev->end);
+		else
+			entry_start = start;
+		start = next->end;
+		/* Reserve the region if non-empty. */
+		if (entry_start != entry_end) {
+			error = iommu_gas_reserve_region_locked(domain,
+			    entry_start, entry_end, entry);
+			if (error != 0)
+				break;
+			entry = NULL;
+		}
+		IOMMU_DOMAIN_UNLOCK(domain);
+	}
+	/* Release a preallocated entry if it was not used. */
+	if (entry != NULL)
+		iommu_gas_free_entry(domain, entry);
+	return (error);
+}
+
 struct iommu_map_entry *
 iommu_map_alloc_entry(struct iommu_domain *domain, u_int flags)
 {