diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
index 2fe459df3c85..18ba0c2328fb 100644
--- a/security/selinux/ss/mls.c
+++ b/security/selinux/ss/mls.c
@@ -436,16 +436,17 @@ int mls_setup_user_range(struct policydb *p,
 
 /*
  * Convert the MLS fields in the security context
- * structure `c' from the values specified in the
- * policy `oldp' to the values specified in the policy `newp'.
+ * structure `oldc' from the values specified in the
+ * policy `oldp' to the values specified in the policy `newp',
+ * storing the resulting context in `newc'.
  */
 int mls_convert_context(struct policydb *oldp,
 			struct policydb *newp,
-			struct context *c)
+			struct context *oldc,
+			struct context *newc)
 {
 	struct level_datum *levdatum;
 	struct cat_datum *catdatum;
-	struct ebitmap bitmap;
 	struct ebitmap_node *node;
 	int l, i;
 
@@ -455,28 +456,25 @@ int mls_convert_context(struct policydb *oldp,
 	for (l = 0; l < 2; l++) {
 		levdatum = hashtab_search(newp->p_levels.table,
 					  sym_name(oldp, SYM_LEVELS,
-						   c->range.level[l].sens - 1));
+						   oldc->range.level[l].sens - 1));
 
 		if (!levdatum)
 			return -EINVAL;
-		c->range.level[l].sens = levdatum->level->sens;
+		newc->range.level[l].sens = levdatum->level->sens;
 
-		ebitmap_init(&bitmap);
-		ebitmap_for_each_positive_bit(&c->range.level[l].cat, node, i) {
+		ebitmap_for_each_positive_bit(&oldc->range.level[l].cat,
+					      node, i) {
 			int rc;
 
 			catdatum = hashtab_search(newp->p_cats.table,
 						  sym_name(oldp, SYM_CATS, i));
 			if (!catdatum)
 				return -EINVAL;
-			rc = ebitmap_set_bit(&bitmap, catdatum->value - 1, 1);
+			rc = ebitmap_set_bit(&newc->range.level[l].cat,
+					     catdatum->value - 1, 1);
 			if (rc)
 				return rc;
-
-			cond_resched();
 		}
-		ebitmap_destroy(&c->range.level[l].cat);
-		c->range.level[l].cat = bitmap;
 	}
 
 	return 0;
diff --git a/security/selinux/ss/mls.h b/security/selinux/ss/mls.h
index 67093647576d..7954b1e60b64 100644
--- a/security/selinux/ss/mls.h
+++ b/security/selinux/ss/mls.h
@@ -46,7 +46,8 @@ int mls_range_set(struct context *context, struct mls_range *range);
 
 int mls_convert_context(struct policydb *oldp,
 			struct policydb *newp,
-			struct context *context);
+			struct context *oldc,
+			struct context *newc);
 
 int mls_compute_sid(struct policydb *p,
 		    struct context *scontext,
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 4ff4b0edbf6b..dd44126c8d14 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -1907,19 +1907,16 @@ struct convert_context_args {
 
 /*
  * Convert the values in the security context
- * structure `c' from the values specified
+ * structure `oldc' from the values specified
  * in the policy `p->oldp' to the values specified
- * in the policy `p->newp'.  Verify that the
- * context is valid under the new policy.
+ * in the policy `p->newp', storing the new context
+ * in `newc'.  Verify that the context is valid
+ * under the new policy.
  */
-static int convert_context(u32 key,
-			   struct context *c,
-			   void *p)
+static int convert_context(struct context *oldc, struct context *newc, void *p)
 {
 	struct convert_context_args *args;
-	struct context oldc;
 	struct ocontext *oc;
-	struct mls_range *range;
 	struct role_datum *role;
 	struct type_datum *typdatum;
 	struct user_datum *usrdatum;
@@ -1929,76 +1926,65 @@ static int convert_context(u32 key,
 
 	args = p;
 
-	if (c->str) {
-		struct context ctx;
-
-		rc = -ENOMEM;
-		s = kstrdup(c->str, GFP_KERNEL);
+	if (oldc->str) {
+		s = kstrdup(oldc->str, GFP_KERNEL);
 		if (!s)
-			goto out;
+			return -ENOMEM;
 
 		rc = string_to_context_struct(args->newp, NULL, s,
-					      &ctx, SECSID_NULL);
-		kfree(s);
-		if (!rc) {
-			pr_info("SELinux:  Context %s became valid (mapped).\n",
-			       c->str);
-			/* Replace string with mapped representation. */
-			kfree(c->str);
-			memcpy(c, &ctx, sizeof(*c));
-			goto out;
-		} else if (rc == -EINVAL) {
+					      newc, SECSID_NULL);
+		if (rc == -EINVAL) {
 			/* Retain string representation for later mapping. */
-			rc = 0;
-			goto out;
-		} else {
+			context_init(newc);
+			newc->str = s;
+			newc->len = oldc->len;
+			return 0;
+		}
+		kfree(s);
+		if (rc) {
 			/* Other error condition, e.g. ENOMEM. */
 			pr_err("SELinux:   Unable to map context %s, rc = %d.\n",
-			       c->str, -rc);
-			goto out;
+			       oldc->str, -rc);
+			return rc;
 		}
+		pr_info("SELinux:  Context %s became valid (mapped).\n",
+			oldc->str);
+		return 0;
 	}
 
-	rc = context_cpy(&oldc, c);
-	if (rc)
-		goto out;
+	context_init(newc);
 
 	/* Convert the user. */
 	rc = -EINVAL;
 	usrdatum = hashtab_search(args->newp->p_users.table,
-				  sym_name(args->oldp, SYM_USERS, c->user - 1));
+				  sym_name(args->oldp,
+					   SYM_USERS, oldc->user - 1));
 	if (!usrdatum)
 		goto bad;
-	c->user = usrdatum->value;
+	newc->user = usrdatum->value;
 
 	/* Convert the role. */
 	rc = -EINVAL;
 	role = hashtab_search(args->newp->p_roles.table,
-			      sym_name(args->oldp, SYM_ROLES, c->role - 1));
+			      sym_name(args->oldp, SYM_ROLES, oldc->role - 1));
 	if (!role)
 		goto bad;
-	c->role = role->value;
+	newc->role = role->value;
 
 	/* Convert the type. */
 	rc = -EINVAL;
 	typdatum = hashtab_search(args->newp->p_types.table,
-				  sym_name(args->oldp, SYM_TYPES, c->type - 1));
+				  sym_name(args->oldp,
+					   SYM_TYPES, oldc->type - 1));
 	if (!typdatum)
 		goto bad;
-	c->type = typdatum->value;
+	newc->type = typdatum->value;
 
 	/* Convert the MLS fields if dealing with MLS policies */
 	if (args->oldp->mls_enabled && args->newp->mls_enabled) {
-		rc = mls_convert_context(args->oldp, args->newp, c);
+		rc = mls_convert_context(args->oldp, args->newp, oldc, newc);
 		if (rc)
 			goto bad;
-	} else if (args->oldp->mls_enabled && !args->newp->mls_enabled) {
-		/*
-		 * Switching between MLS and non-MLS policy:
-		 * free any storage used by the MLS fields in the
-		 * context for all existing entries in the sidtab.
-		 */
-		mls_context_destroy(c);
 	} else if (!args->oldp->mls_enabled && args->newp->mls_enabled) {
 		/*
 		 * Switching between non-MLS and MLS policy:
@@ -2016,38 +2002,30 @@ static int convert_context(u32 key,
 				" the initial SIDs list\n");
 			goto bad;
 		}
-		range = &oc->context[0].range;
-		rc = mls_range_set(c, range);
+		rc = mls_range_set(newc, &oc->context[0].range);
 		if (rc)
 			goto bad;
 	}
 
 	/* Check the validity of the new context. */
-	if (!policydb_context_isvalid(args->newp, c)) {
-		rc = convert_context_handle_invalid_context(args->state,
-							    &oldc);
+	if (!policydb_context_isvalid(args->newp, newc)) {
+		rc = convert_context_handle_invalid_context(args->state, oldc);
 		if (rc)
 			goto bad;
 	}
 
-	context_destroy(&oldc);
-
-	rc = 0;
-out:
-	return rc;
+	return 0;
 bad:
 	/* Map old representation to string and save it. */
-	rc = context_struct_to_string(args->oldp, &oldc, &s, &len);
+	rc = context_struct_to_string(args->oldp, oldc, &s, &len);
 	if (rc)
 		return rc;
-	context_destroy(&oldc);
-	context_destroy(c);
-	c->str = s;
-	c->len = len;
+	context_destroy(newc);
+	newc->str = s;
+	newc->len = len;
 	pr_info("SELinux:  Context %s became invalid (unmapped).\n",
-	       c->str);
-	rc = 0;
-	goto out;
+		newc->str);
+	return 0;
 }
 
 static void security_load_policycaps(struct selinux_state *state)
@@ -2091,6 +2069,7 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len)
 	struct policydb *oldpolicydb, *newpolicydb;
 	struct selinux_mapping *oldmapping;
 	struct selinux_map newmap;
+	struct sidtab_convert_params convert_params;
 	struct convert_context_args args;
 	u32 seqno;
 	int rc = 0;
@@ -2147,12 +2126,6 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len)
 		goto out;
 	}
 
-	oldsidtab = state->ss->sidtab;
-
-#if 0
-	sidtab_hash_eval(oldsidtab, "sids");
-#endif
-
 	rc = policydb_read(newpolicydb, fp);
 	if (rc) {
 		kfree(newsidtab);
@@ -2184,6 +2157,8 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len)
 		goto err;
 	}
 
+	oldsidtab = state->ss->sidtab;
+
 	/*
 	 * Convert the internal representations of contexts
 	 * in the new SID table.
@@ -2191,7 +2166,12 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len)
 	args.state = state;
 	args.oldp = policydb;
 	args.newp = newpolicydb;
-	rc = sidtab_convert(oldsidtab, newsidtab, convert_context, &args);
+
+	convert_params.func = convert_context;
+	convert_params.args = &args;
+	convert_params.target = newsidtab;
+
+	rc = sidtab_convert(oldsidtab, &convert_params);
 	if (rc) {
 		pr_err("SELinux:  unable to convert the internal"
 			" representation of contexts in the new SID"
diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
index e44e7cec630c..e63a90ff2728 100644
--- a/security/selinux/ss/sidtab.c
+++ b/security/selinux/ss/sidtab.c
@@ -2,88 +2,41 @@
 /*
  * Implementation of the SID table type.
  *
- * Author : Stephen Smalley, <sds@tycho.nsa.gov>
+ * Original author: Stephen Smalley, <sds@tycho.nsa.gov>
+ * Author: Ondrej Mosnacek, <omosnacek@gmail.com>
+ *
+ * Copyright (C) 2018 Red Hat, Inc.
  */
+#include <linux/errno.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
+#include <linux/sched.h>
 #include <linux/spinlock.h>
-#include <linux/errno.h>
+#include <linux/atomic.h>
 #include "flask.h"
 #include "security.h"
 #include "sidtab.h"
 
-#define SIDTAB_HASH(sid) \
-(sid & SIDTAB_HASH_MASK)
-
 int sidtab_init(struct sidtab *s)
 {
-	int i;
+	u32 i;
 
-	s->htable = kmalloc_array(SIDTAB_SIZE, sizeof(*s->htable), GFP_ATOMIC);
-	if (!s->htable)
-		return -ENOMEM;
+	memset(s->roots, 0, sizeof(s->roots));
+
+	for (i = 0; i < SIDTAB_RCACHE_SIZE; i++)
+		atomic_set(&s->rcache[i], -1);
 
 	for (i = 0; i < SECINITSID_NUM; i++)
 		s->isids[i].set = 0;
 
-	for (i = 0; i < SIDTAB_SIZE; i++)
-		s->htable[i] = NULL;
+	atomic_set(&s->count, 0);
 
-	for (i = 0; i < SIDTAB_CACHE_LEN; i++)
-		s->cache[i] = NULL;
+	s->convert = NULL;
 
-	s->nel = 0;
-	s->next_sid = 0;
-	s->shutdown = 0;
 	spin_lock_init(&s->lock);
 	return 0;
 }
 
-static int sidtab_insert(struct sidtab *s, u32 sid, struct context *context)
-{
-	int hvalue;
-	struct sidtab_node *prev, *cur, *newnode;
-
-	if (!s)
-		return -ENOMEM;
-
-	hvalue = SIDTAB_HASH(sid);
-	prev = NULL;
-	cur = s->htable[hvalue];
-	while (cur && sid > cur->sid) {
-		prev = cur;
-		cur = cur->next;
-	}
-
-	if (cur && sid == cur->sid)
-		return -EEXIST;
-
-	newnode = kmalloc(sizeof(*newnode), GFP_ATOMIC);
-	if (!newnode)
-		return -ENOMEM;
-
-	newnode->sid = sid;
-	if (context_cpy(&newnode->context, context)) {
-		kfree(newnode);
-		return -ENOMEM;
-	}
-
-	if (prev) {
-		newnode->next = prev->next;
-		wmb();
-		prev->next = newnode;
-	} else {
-		newnode->next = s->htable[hvalue];
-		wmb();
-		s->htable[hvalue] = newnode;
-	}
-
-	s->nel++;
-	if (sid >= s->next_sid)
-		s->next_sid = sid + 1;
-	return 0;
-}
-
 int sidtab_set_initial(struct sidtab *s, u32 sid, struct context *context)
 {
 	struct sidtab_isid_entry *entry;
@@ -102,20 +55,90 @@ int sidtab_set_initial(struct sidtab *s, u32 sid, struct context *context)
 	return 0;
 }
 
-static struct context *sidtab_lookup(struct sidtab *s, u32 sid)
+static u32 sidtab_level_from_count(u32 count)
 {
-	int hvalue;
-	struct sidtab_node *cur;
+	u32 capacity = SIDTAB_LEAF_ENTRIES;
+	u32 level = 0;
 
-	hvalue = SIDTAB_HASH(sid);
-	cur = s->htable[hvalue];
-	while (cur && sid > cur->sid)
-		cur = cur->next;
+	while (count > capacity) {
+		capacity <<= SIDTAB_INNER_SHIFT;
+		++level;
+	}
+	return level;
+}
 
-	if (!cur || sid != cur->sid)
+static int sidtab_alloc_roots(struct sidtab *s, u32 level)
+{
+	u32 l;
+
+	if (!s->roots[0].ptr_leaf) {
+		s->roots[0].ptr_leaf = kzalloc(SIDTAB_NODE_ALLOC_SIZE,
+					       GFP_ATOMIC);
+		if (!s->roots[0].ptr_leaf)
+			return -ENOMEM;
+	}
+	for (l = 1; l <= level; ++l)
+		if (!s->roots[l].ptr_inner) {
+			s->roots[l].ptr_inner = kzalloc(SIDTAB_NODE_ALLOC_SIZE,
+							GFP_ATOMIC);
+			if (!s->roots[l].ptr_inner)
+				return -ENOMEM;
+			s->roots[l].ptr_inner->entries[0] = s->roots[l - 1];
+		}
+	return 0;
+}
+
+static struct context *sidtab_do_lookup(struct sidtab *s, u32 index, int alloc)
+{
+	union sidtab_entry_inner *entry;
+	u32 level, capacity_shift, leaf_index = index / SIDTAB_LEAF_ENTRIES;
+
+	/* find the level of the subtree we need */
+	level = sidtab_level_from_count(index + 1);
+	capacity_shift = level * SIDTAB_INNER_SHIFT;
+
+	/* allocate roots if needed */
+	if (alloc && sidtab_alloc_roots(s, level) != 0)
 		return NULL;
 
-	return &cur->context;
+	/* lookup inside the subtree */
+	entry = &s->roots[level];
+	while (level != 0) {
+		capacity_shift -= SIDTAB_INNER_SHIFT;
+		--level;
+
+		entry = &entry->ptr_inner->entries[leaf_index >> capacity_shift];
+		leaf_index &= ((u32)1 << capacity_shift) - 1;
+
+		if (!entry->ptr_inner) {
+			if (alloc)
+				entry->ptr_inner = kzalloc(SIDTAB_NODE_ALLOC_SIZE,
+							   GFP_ATOMIC);
+			if (!entry->ptr_inner)
+				return NULL;
+		}
+	}
+	if (!entry->ptr_leaf) {
+		if (alloc)
+			entry->ptr_leaf = kzalloc(SIDTAB_NODE_ALLOC_SIZE,
+						  GFP_ATOMIC);
+		if (!entry->ptr_leaf)
+			return NULL;
+	}
+	return &entry->ptr_leaf->entries[index % SIDTAB_LEAF_ENTRIES].context;
+}
+
+static struct context *sidtab_lookup(struct sidtab *s, u32 index)
+{
+	u32 count = (u32)atomic_read(&s->count);
+
+	if (index >= count)
+		return NULL;
+
+	/* read entries after reading count */
+	smp_rmb();
+
+	return sidtab_do_lookup(s, index, 0);
 }
 
 static struct context *sidtab_lookup_initial(struct sidtab *s, u32 sid)
@@ -127,9 +150,6 @@ static struct context *sidtab_search_core(struct sidtab *s, u32 sid, int force)
 {
 	struct context *context;
 
-	if (!s)
-		return NULL;
-
 	if (sid != 0) {
 		if (sid > SECINITSID_NUM)
 			context = sidtab_lookup(s, sid - (SECINITSID_NUM + 1));
@@ -152,102 +172,69 @@ struct context *sidtab_search_force(struct sidtab *s, u32 sid)
 	return sidtab_search_core(s, sid, 1);
 }
 
-static int sidtab_map(struct sidtab *s,
-		      int (*apply)(u32 sid,
-				   struct context *context,
-				   void *args),
-		      void *args)
+static int sidtab_find_context(union sidtab_entry_inner entry,
+			       u32 *pos, u32 count, u32 level,
+			       struct context *context, u32 *index)
 {
-	int i, rc = 0;
-	struct sidtab_node *cur;
-
-	if (!s)
-		goto out;
-
-	for (i = 0; i < SIDTAB_SIZE; i++) {
-		cur = s->htable[i];
-		while (cur) {
-			rc = apply(cur->sid, &cur->context, args);
-			if (rc)
-				goto out;
-			cur = cur->next;
-		}
-	}
-out:
-	return rc;
-}
-
-/* Clone the SID into the new SID table. */
-static int clone_sid(u32 sid, struct context *context, void *arg)
-{
-	struct sidtab *s = arg;
-	return sidtab_insert(s, sid, context);
-}
-
-int sidtab_convert(struct sidtab *s, struct sidtab *news,
-		   int (*convert)(u32 sid,
-				  struct context *context,
-				  void *args),
-		   void *args)
-{
-	unsigned long flags;
 	int rc;
+	u32 i;
 
-	spin_lock_irqsave(&s->lock, flags);
-	s->shutdown = 1;
-	spin_unlock_irqrestore(&s->lock, flags);
+	if (level != 0) {
+		struct sidtab_node_inner *node = entry.ptr_inner;
 
-	rc = sidtab_map(s, clone_sid, news);
-	if (rc)
-		return rc;
+		i = 0;
+		while (i < SIDTAB_INNER_ENTRIES && *pos < count) {
+			rc = sidtab_find_context(node->entries[i],
+						 pos, count, level - 1,
+						 context, index);
+			if (rc == 0)
+				return 0;
+			i++;
+		}
+	} else {
+		struct sidtab_node_leaf *node = entry.ptr_leaf;
 
-	return sidtab_map(news, convert, args);
-}
-
-static void sidtab_update_cache(struct sidtab *s, struct sidtab_node *n, int loc)
-{
-	BUG_ON(loc >= SIDTAB_CACHE_LEN);
-
-	while (loc > 0) {
-		s->cache[loc] = s->cache[loc - 1];
-		loc--;
-	}
-	s->cache[0] = n;
-}
-
-static inline int sidtab_search_context(struct sidtab *s,
-					struct context *context, u32 *sid)
-{
-	int i;
-	struct sidtab_node *cur;
-
-	for (i = 0; i < SIDTAB_SIZE; i++) {
-		cur = s->htable[i];
-		while (cur) {
-			if (context_cmp(&cur->context, context)) {
-				sidtab_update_cache(s, cur, SIDTAB_CACHE_LEN - 1);
-				*sid = cur->sid;
+		i = 0;
+		while (i < SIDTAB_LEAF_ENTRIES && *pos < count) {
+			if (context_cmp(&node->entries[i].context, context)) {
+				*index = *pos;
 				return 0;
 			}
-			cur = cur->next;
+			(*pos)++;
+			i++;
 		}
 	}
 	return -ENOENT;
 }
 
-static inline int sidtab_search_cache(struct sidtab *s, struct context *context,
-				      u32 *sid)
+static void sidtab_rcache_update(struct sidtab *s, u32 index, u32 pos)
 {
-	int i;
-	struct sidtab_node *node;
+	while (pos > 0) {
+		atomic_set(&s->rcache[pos], atomic_read(&s->rcache[pos - 1]));
+		--pos;
+	}
+	atomic_set(&s->rcache[0], (int)index);
+}
 
-	for (i = 0; i < SIDTAB_CACHE_LEN; i++) {
-		node = s->cache[i];
-		if (unlikely(!node))
-			return -ENOENT;
-		if (context_cmp(&node->context, context)) {
-			sidtab_update_cache(s, node, i);
-			*sid = node->sid;
+static void sidtab_rcache_push(struct sidtab *s, u32 index)
+{
+	sidtab_rcache_update(s, index, SIDTAB_RCACHE_SIZE - 1);
+}
+
+static int sidtab_rcache_search(struct sidtab *s, struct context *context,
+				u32 *index)
+{
+	u32 i;
+
+	for (i = 0; i < SIDTAB_RCACHE_SIZE; i++) {
+		int v = atomic_read(&s->rcache[i]);
+
+		if (v < 0)
+			continue;
+
+		if (context_cmp(sidtab_do_lookup(s, (u32)v, 0), context)) {
+			sidtab_rcache_update(s, (u32)v, i);
+			*index = (u32)v;
 			return 0;
 		}
 	}
@@ -255,38 +242,98 @@ static inline int sidtab_search_cache(struct sidtab *s, struct context *context,
 }
 
 static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
-				 u32 *sid)
+				 u32 *index)
 {
-	int ret;
 	unsigned long flags;
+	u32 count = (u32)atomic_read(&s->count);
+	u32 count_locked, level, pos;
+	struct sidtab_convert_params *convert;
+	struct context *dst, *dst_convert;
+	int rc;
 
-	ret = sidtab_search_cache(s, context, sid);
-	if (ret)
-		ret = sidtab_search_context(s, context, sid);
-	if (ret) {
-		spin_lock_irqsave(&s->lock, flags);
-		/* Rescan now that we hold the lock. */
-		ret = sidtab_search_context(s, context, sid);
-		if (!ret)
-			goto unlock_out;
-		/* No SID exists for the context.  Allocate a new one. */
-		if (s->next_sid == (UINT_MAX - SECINITSID_NUM - 1) ||
-		    s->shutdown) {
-			ret = -ENOMEM;
-			goto unlock_out;
-		}
-		*sid = s->next_sid++;
-		if (context->len)
-			pr_info("SELinux:  Context %s is not valid (left unmapped).\n",
-			       context->str);
-		ret = sidtab_insert(s, *sid, context);
-		if (ret)
-			s->next_sid--;
-unlock_out:
-		spin_unlock_irqrestore(&s->lock, flags);
+	rc = sidtab_rcache_search(s, context, index);
+	if (rc == 0)
+		return 0;
+
+	level = sidtab_level_from_count(count);
+
+	/* read entries after reading count */
+	smp_rmb();
+
+	pos = 0;
+	rc = sidtab_find_context(s->roots[level], &pos, count, level,
+				 context, index);
+	if (rc == 0) {
+		sidtab_rcache_push(s, *index);
+		return 0;
 	}
 
-	return ret;
+	/* lock-free search failed: lock, re-search, and insert if not found */
+	spin_lock_irqsave(&s->lock, flags);
+
+	convert = s->convert;
+	count_locked = (u32)atomic_read(&s->count);
+	level = sidtab_level_from_count(count_locked);
+
+	/* if count has changed before we acquired the lock, then catch up */
+	while (count < count_locked) {
+		if (context_cmp(sidtab_do_lookup(s, count, 0), context)) {
+			sidtab_rcache_push(s, count);
+			*index = count;
+			rc = 0;
+			goto out_unlock;
+		}
+		++count;
+	}
+
+	/* insert context into new entry */
+	rc = -ENOMEM;
+	dst = sidtab_do_lookup(s, count, 1);
+	if (!dst)
+		goto out_unlock;
+
+	rc = context_cpy(dst, context);
+	if (rc)
+		goto out_unlock;
+
+	/*
+	 * if we are building a new sidtab, we need to convert the context
+	 * and insert it there as well
+	 */
+	if (convert) {
+		rc = -ENOMEM;
+		dst_convert = sidtab_do_lookup(convert->target, count, 1);
+		if (!dst_convert) {
+			context_destroy(dst);
+			goto out_unlock;
+		}
+
+		rc = convert->func(context, dst_convert, convert->args);
+		if (rc) {
+			context_destroy(dst);
+			goto out_unlock;
+		}
+
+		/* at this point we know the insert won't fail */
+		atomic_set(&convert->target->count, count + 1);
+	}
+
+	if (context->len)
+		pr_info("SELinux:  Context %s is not valid (left unmapped).\n",
+			context->str);
+
+	sidtab_rcache_push(s, count);
+	*index = count;
+
+	/* write entries before writing new count */
+	smp_wmb();
+
+	atomic_set(&s->count, count + 1);
+
+	rc = 0;
+out_unlock:
+	spin_unlock_irqrestore(&s->lock, flags);
+	return rc;
 }
 
 int sidtab_context_to_sid(struct sidtab *s, struct context *context, u32 *sid)
@@ -310,57 +357,139 @@ int sidtab_context_to_sid(struct sidtab *s, struct context *context, u32 *sid)
 	return 0;
 }
 
-void sidtab_hash_eval(struct sidtab *h, char *tag)
+static int sidtab_convert_tree(union sidtab_entry_inner *edst,
+			       union sidtab_entry_inner *esrc,
+			       u32 *pos, u32 count, u32 level,
+			       struct sidtab_convert_params *convert)
 {
-	int i, chain_len, slots_used, max_chain_len;
-	struct sidtab_node *cur;
+	int rc;
+	u32 i;
 
-	slots_used = 0;
-	max_chain_len = 0;
-	for (i = 0; i < SIDTAB_SIZE; i++) {
-		cur = h->htable[i];
-		if (cur) {
-			slots_used++;
-			chain_len = 0;
-			while (cur) {
-				chain_len++;
-				cur = cur->next;
-			}
-
-			if (chain_len > max_chain_len)
-				max_chain_len = chain_len;
+	if (level != 0) {
+		if (!edst->ptr_inner) {
+			edst->ptr_inner = kzalloc(SIDTAB_NODE_ALLOC_SIZE,
+						  GFP_KERNEL);
+			if (!edst->ptr_inner)
+				return -ENOMEM;
 		}
+		i = 0;
+		while (i < SIDTAB_INNER_ENTRIES && *pos < count) {
+			rc = sidtab_convert_tree(&edst->ptr_inner->entries[i],
+						 &esrc->ptr_inner->entries[i],
+						 pos, count, level - 1,
+						 convert);
+			if (rc)
+				return rc;
+			i++;
+		}
+	} else {
+		if (!edst->ptr_leaf) {
+			edst->ptr_leaf = kzalloc(SIDTAB_NODE_ALLOC_SIZE,
+						 GFP_KERNEL);
+			if (!edst->ptr_leaf)
+				return -ENOMEM;
+		}
+		i = 0;
+		while (i < SIDTAB_LEAF_ENTRIES && *pos < count) {
+			rc = convert->func(&esrc->ptr_leaf->entries[i].context,
+					   &edst->ptr_leaf->entries[i].context,
+					   convert->args);
+			if (rc)
+				return rc;
+			(*pos)++;
+			i++;
+		}
+		cond_resched();
+	}
+	return 0;
+}
+
+int sidtab_convert(struct sidtab *s, struct sidtab_convert_params *params)
+{
+	unsigned long flags;
+	u32 count, level, pos;
+	int rc;
+
+	spin_lock_irqsave(&s->lock, flags);
+
+	/* concurrent policy loads are not allowed */
+	if (s->convert) {
+		spin_unlock_irqrestore(&s->lock, flags);
+		return -EBUSY;
 	}
 
-	pr_debug("%s:  %d entries and %d/%d buckets used, longest "
-	       "chain length %d\n", tag, h->nel, slots_used, SIDTAB_SIZE,
-	       max_chain_len);
+	count = (u32)atomic_read(&s->count);
+	level = sidtab_level_from_count(count);
+
+	/* allocate last leaf in the new sidtab (to avoid race with
+	 * live convert)
+	 */
+	rc = sidtab_do_lookup(params->target, count - 1, 1) ? 0 : -ENOMEM;
+	if (rc) {
+		spin_unlock_irqrestore(&s->lock, flags);
+		return rc;
+	}
+
+	/* set count in case no new entries are added during conversion */
+	atomic_set(&params->target->count, count);
+
+	/* enable live convert of new entries */
+	s->convert = params;
+
+	/* we can safely do the rest of the conversion outside the lock */
+	spin_unlock_irqrestore(&s->lock, flags);
+
+	pr_info("SELinux:  Converting %u SID table entries...\n", count);
+
+	/* convert all entries not covered by live convert */
+	pos = 0;
+	rc = sidtab_convert_tree(&params->target->roots[level],
+				 &s->roots[level], &pos, count, level, params);
+	if (rc) {
+		/* we need to keep the old table - disable live convert */
+		spin_lock_irqsave(&s->lock, flags);
+		s->convert = NULL;
+		spin_unlock_irqrestore(&s->lock, flags);
+	}
+	return rc;
+}
+
+static void sidtab_destroy_tree(union sidtab_entry_inner entry, u32 level)
+{
+	u32 i;
+
+	if (level != 0) {
+		struct sidtab_node_inner *node = entry.ptr_inner;
+
+		if (!node)
+			return;
+
+		for (i = 0; i < SIDTAB_INNER_ENTRIES; i++)
+			sidtab_destroy_tree(node->entries[i], level - 1);
+		kfree(node);
+	} else {
+		struct sidtab_node_leaf *node = entry.ptr_leaf;
+
+		if (!node)
+			return;
+
+		for (i = 0; i < SIDTAB_LEAF_ENTRIES; i++)
+			context_destroy(&node->entries[i].context);
+		kfree(node);
+	}
 }
 
 void sidtab_destroy(struct sidtab *s)
 {
-	int i;
-	struct sidtab_node *cur, *temp;
-
-	if (!s)
-		return;
+	u32 i, level;
 
 	for (i = 0; i < SECINITSID_NUM; i++)
 		if (s->isids[i].set)
 			context_destroy(&s->isids[i].context);
 
-	for (i = 0; i < SIDTAB_SIZE; i++) {
-		cur = s->htable[i];
-		while (cur) {
-			temp = cur;
-			cur = cur->next;
-			context_destroy(&temp->context);
-			kfree(temp);
-		}
-		s->htable[i] = NULL;
-	}
-	kfree(s->htable);
-	s->htable = NULL;
-	s->nel = 0;
-	s->next_sid = 1;
+	level = SIDTAB_MAX_LEVEL;
+	while (level && !s->roots[level].ptr_inner)
+		--level;
+
+	sidtab_destroy_tree(s->roots[level], level);
 }
diff --git a/security/selinux/ss/sidtab.h b/security/selinux/ss/sidtab.h
index e657ae6bf996..bbd5c0d1f3bd 100644
--- a/security/selinux/ss/sidtab.h
+++ b/security/selinux/ss/sidtab.h
@@ -1,41 +1,82 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * A security identifier table (sidtab) is a hash table
+ * A security identifier table (sidtab) is a lookup table
  * of security context structures indexed by SID value.
  *
- * Author : Stephen Smalley, <sds@tycho.nsa.gov>
+ * Original author: Stephen Smalley, <sds@tycho.nsa.gov>
+ * Author: Ondrej Mosnacek, <omosnacek@gmail.com>
+ *
+ * Copyright (C) 2018 Red Hat, Inc.
  */
 #ifndef _SS_SIDTAB_H_
 #define _SS_SIDTAB_H_
 
+#include <linux/spinlock_types.h>
+#include <linux/log2.h>
+
 #include "context.h"
 
-struct sidtab_node {
-	u32 sid;		/* security identifier */
-	struct context context;	/* security context structure */
-	struct sidtab_node *next;
+struct sidtab_entry_leaf {
+	struct context context;
 };
 
-#define SIDTAB_HASH_BITS 7
-#define SIDTAB_HASH_BUCKETS (1 << SIDTAB_HASH_BITS)
-#define SIDTAB_HASH_MASK (SIDTAB_HASH_BUCKETS-1)
+struct sidtab_node_inner;
+struct sidtab_node_leaf;
 
-#define SIDTAB_SIZE SIDTAB_HASH_BUCKETS
+union sidtab_entry_inner {
+	struct sidtab_node_inner *ptr_inner;
+	struct sidtab_node_leaf  *ptr_leaf;
+};
+
+/* align node size to page boundary */
+#define SIDTAB_NODE_ALLOC_SHIFT PAGE_SHIFT
+#define SIDTAB_NODE_ALLOC_SIZE  PAGE_SIZE
+
+#define size_to_shift(size) ((size) == 1 ? 1 : (const_ilog2((size) - 1) + 1))
+
+#define SIDTAB_INNER_SHIFT \
+	(SIDTAB_NODE_ALLOC_SHIFT - size_to_shift(sizeof(union sidtab_entry_inner)))
+#define SIDTAB_INNER_ENTRIES ((size_t)1 << SIDTAB_INNER_SHIFT)
+#define SIDTAB_LEAF_ENTRIES \
+	(SIDTAB_NODE_ALLOC_SIZE / sizeof(struct sidtab_entry_leaf))
+
+#define SIDTAB_MAX_BITS 31 /* limited to INT_MAX due to atomic_t range */
+#define SIDTAB_MAX (((u32)1 << SIDTAB_MAX_BITS) - 1)
+/* ensure enough tree levels for SIDTAB_MAX entries */
+#define SIDTAB_MAX_LEVEL \
+	DIV_ROUND_UP(SIDTAB_MAX_BITS - size_to_shift(SIDTAB_LEAF_ENTRIES), \
+		     SIDTAB_INNER_SHIFT)
+
+struct sidtab_node_leaf {
+	struct sidtab_entry_leaf entries[SIDTAB_LEAF_ENTRIES];
+};
+
+struct sidtab_node_inner {
+	union sidtab_entry_inner entries[SIDTAB_INNER_ENTRIES];
+};
 
 struct sidtab_isid_entry {
 	int set;
 	struct context context;
 };
 
+struct sidtab_convert_params {
+	int (*func)(struct context *oldc, struct context *newc, void *args);
+	void *args;
+	struct sidtab *target;
+};
+
+#define SIDTAB_RCACHE_SIZE 3
+
 struct sidtab {
-	struct sidtab_node **htable;
-	unsigned int nel;	/* number of elements */
-	unsigned int next_sid;	/* next SID to allocate */
-	unsigned char shutdown;
-#define SIDTAB_CACHE_LEN	3
-	struct sidtab_node *cache[SIDTAB_CACHE_LEN];
+	union sidtab_entry_inner roots[SIDTAB_MAX_LEVEL + 1];
+	atomic_t count;
+	struct sidtab_convert_params *convert;
 	spinlock_t lock;
 
+	/* reverse lookup cache */
+	atomic_t rcache[SIDTAB_RCACHE_SIZE];
+
 	/* index == SID - 1 (no entry for SECSID_NULL) */
 	struct sidtab_isid_entry isids[SECINITSID_NUM];
 };
@@ -45,15 +86,10 @@ int sidtab_set_initial(struct sidtab *s, u32 sid, struct context *context);
 struct context *sidtab_search(struct sidtab *s, u32 sid);
 struct context *sidtab_search_force(struct sidtab *s, u32 sid);
 
-int sidtab_convert(struct sidtab *s, struct sidtab *news,
-		   int (*apply)(u32 sid,
-				struct context *context,
-				void *args),
-		   void *args);
+int sidtab_convert(struct sidtab *s, struct sidtab_convert_params *params);
 
 int sidtab_context_to_sid(struct sidtab *s, struct context *context, u32 *sid);
 
-void sidtab_hash_eval(struct sidtab *h, char *tag);
 void sidtab_destroy(struct sidtab *s);
 
 #endif	/* _SS_SIDTAB_H_ */