mac80211: implement multi-vif in-place reservations

Multi-vif in-place reservations happen when
it is impossible to allocate more channel contexts
as indicated by interface combinations.

Such reservations are not finalized until all
assigned interfaces are ready.

This still doesn't handle all possible cases
(i.e. degradation of number of channels) properly.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

3 files changed, 715 insertions, 85 deletions

diff --git a/net/mac80211/chan.c b/net/mac80211/chan.c
index a310e33972de..0e4302bb5b34 100644
--- a/net/mac80211/chan.c
+++ b/net/mac80211/chan.c
@@ -63,6 +63,20 @@ static bool ieee80211_can_create_new_chanctx(struct ieee80211_local *local)
 	return ieee80211_num_chanctx(local) < ieee80211_max_num_channels(local);
 }
 
+static struct ieee80211_chanctx *
+ieee80211_vif_get_chanctx(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_local *local = sdata->local;
+	struct ieee80211_chanctx_conf *conf;
+
+	conf = rcu_dereference_protected(sdata->vif.chanctx_conf,
+					 lockdep_is_held(&local->chanctx_mtx));
+	if (!conf)
+		return NULL;
+
+	return container_of(conf, struct ieee80211_chanctx, conf);
+}
+
 static const struct cfg80211_chan_def *
 ieee80211_chanctx_reserved_chandef(struct ieee80211_local *local,
 				   struct ieee80211_chanctx *ctx,
@@ -160,6 +174,9 @@ ieee80211_find_reservation_chanctx(struct ieee80211_local *local,
 		return NULL;
 
 	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state == IEEE80211_CHANCTX_WILL_BE_REPLACED)
+			continue;
+
 		if (ctx->mode == IEEE80211_CHANCTX_EXCLUSIVE)
 			continue;
 
@@ -347,6 +364,9 @@ ieee80211_find_chanctx(struct ieee80211_local *local,
 	list_for_each_entry(ctx, &local->chanctx_list, list) {
 		const struct cfg80211_chan_def *compat;
 
+		if (ctx->replace_state != IEEE80211_CHANCTX_REPLACE_NONE)
+			continue;
+
 		if (ctx->mode == IEEE80211_CHANCTX_EXCLUSIVE)
 			continue;
 
@@ -622,6 +642,7 @@ static void __ieee80211_vif_release_channel(struct ieee80211_sub_if_data *sdata)
 	struct ieee80211_local *local = sdata->local;
 	struct ieee80211_chanctx_conf *conf;
 	struct ieee80211_chanctx *ctx;
+	bool use_reserved_switch = false;
 
 	lockdep_assert_held(&local->chanctx_mtx);
 
@@ -632,12 +653,23 @@ static void __ieee80211_vif_release_channel(struct ieee80211_sub_if_data *sdata)
 
 	ctx = container_of(conf, struct ieee80211_chanctx, conf);
 
-	if (sdata->reserved_chanctx)
+	if (sdata->reserved_chanctx) {
+		if (sdata->reserved_chanctx->replace_state ==
+		    IEEE80211_CHANCTX_REPLACES_OTHER &&
+		    ieee80211_chanctx_num_reserved(local,
+						   sdata->reserved_chanctx) > 1)
+			use_reserved_switch = true;
+
 		ieee80211_vif_unreserve_chanctx(sdata);
+	}
 
 	ieee80211_assign_vif_chanctx(sdata, NULL);
 	if (ieee80211_chanctx_refcount(local, ctx) == 0)
 		ieee80211_free_chanctx(local, ctx);
+
+	/* Unreserving may ready an in-place reservation. */
+	if (use_reserved_switch)
+		ieee80211_vif_use_reserved_switch(local);
 }
 
 void ieee80211_recalc_smps_chanctx(struct ieee80211_local *local,
@@ -905,8 +937,25 @@ int ieee80211_vif_unreserve_chanctx(struct ieee80211_sub_if_data *sdata)
 	list_del(&sdata->reserved_chanctx_list);
 	sdata->reserved_chanctx = NULL;
 
-	if (ieee80211_chanctx_refcount(sdata->local, ctx) == 0)
-		ieee80211_free_chanctx(sdata->local, ctx);
+	if (ieee80211_chanctx_refcount(sdata->local, ctx) == 0) {
+		if (ctx->replace_state == IEEE80211_CHANCTX_REPLACES_OTHER) {
+			if (WARN_ON(!ctx->replace_ctx))
+				return -EINVAL;
+
+			WARN_ON(ctx->replace_ctx->replace_state !=
+			        IEEE80211_CHANCTX_WILL_BE_REPLACED);
+			WARN_ON(ctx->replace_ctx->replace_ctx != ctx);
+
+			ctx->replace_ctx->replace_ctx = NULL;
+			ctx->replace_ctx->replace_state =
+					IEEE80211_CHANCTX_REPLACE_NONE;
+
+			list_del_rcu(&ctx->list);
+			kfree_rcu(ctx, rcu_head);
+		} else {
+			ieee80211_free_chanctx(sdata->local, ctx);
+		}
+	}
 
 	return 0;
 }
@@ -917,40 +966,84 @@ int ieee80211_vif_reserve_chanctx(struct ieee80211_sub_if_data *sdata,
 				  bool radar_required)
 {
 	struct ieee80211_local *local = sdata->local;
-	struct ieee80211_chanctx_conf *conf;
-	struct ieee80211_chanctx *new_ctx, *curr_ctx;
-	int ret = 0;
+	struct ieee80211_chanctx *new_ctx, *curr_ctx, *ctx;
 
-	mutex_lock(&local->chanctx_mtx);
-
-	conf = rcu_dereference_protected(sdata->vif.chanctx_conf,
-					 lockdep_is_held(&local->chanctx_mtx));
-	if (!conf) {
-		ret = -EINVAL;
-		goto out;
-	}
+	lockdep_assert_held(&local->chanctx_mtx);
 
-	curr_ctx = container_of(conf, struct ieee80211_chanctx, conf);
+	curr_ctx = ieee80211_vif_get_chanctx(sdata);
+	if (curr_ctx && local->use_chanctx && !local->ops->switch_vif_chanctx)
+		return -ENOTSUPP;
 
 	new_ctx = ieee80211_find_reservation_chanctx(local, chandef, mode);
 	if (!new_ctx) {
-		if (ieee80211_chanctx_refcount(local, curr_ctx) == 1 &&
-		    (local->hw.flags & IEEE80211_HW_CHANGE_RUNNING_CHANCTX)) {
-			/* if we're the only users of the chanctx and
-			 * the driver supports changing a running
-			 * context, reserve our current context
-			 */
-			new_ctx = curr_ctx;
-		} else if (ieee80211_can_create_new_chanctx(local)) {
-			/* create a new context and reserve it */
+		if (ieee80211_can_create_new_chanctx(local)) {
 			new_ctx = ieee80211_new_chanctx(local, chandef, mode);
-			if (IS_ERR(new_ctx)) {
-				ret = PTR_ERR(new_ctx);
-				goto out;
-			}
+			if (IS_ERR(new_ctx))
+				return PTR_ERR(new_ctx);
 		} else {
-			ret = -EBUSY;
-			goto out;
+			if (!curr_ctx ||
+			    (curr_ctx->replace_state ==
+			     IEEE80211_CHANCTX_WILL_BE_REPLACED) ||
+			    !list_empty(&curr_ctx->reserved_vifs)) {
+				/*
+				 * Another vif already requested this context
+				 * for a reservation. Find another one hoping
+				 * all vifs assigned to it will also switch
+				 * soon enough.
+				 *
+				 * TODO: This needs a little more work as some
+				 * cases (more than 2 chanctx capable devices)
+				 * may fail which could otherwise succeed
+				 * provided some channel context juggling was
+				 * performed.
+				 *
+				 * Consider ctx1..3, vif1..6, each ctx has 2
+				 * vifs. vif1 and vif2 from ctx1 request new
+				 * different chandefs starting 2 in-place
+				 * reserations with ctx4 and ctx5 replacing
+				 * ctx1 and ctx2 respectively. Next vif5 and
+				 * vif6 from ctx3 reserve ctx4. If vif3 and
+				 * vif4 remain on ctx2 as they are then this
+				 * fails unless `replace_ctx` from ctx5 is
+				 * replaced with ctx3.
+				 */
+				list_for_each_entry(ctx, &local->chanctx_list,
+						    list) {
+					if (ctx->replace_state !=
+					    IEEE80211_CHANCTX_REPLACE_NONE)
+						continue;
+
+					if (!list_empty(&ctx->reserved_vifs))
+						continue;
+
+					curr_ctx = ctx;
+					break;
+				}
+			}
+
+			/*
+			 * If that's true then all available contexts already
+			 * have reservations and cannot be used.
+			 */
+			if (!curr_ctx ||
+			    (curr_ctx->replace_state ==
+			     IEEE80211_CHANCTX_WILL_BE_REPLACED) ||
+			    !list_empty(&curr_ctx->reserved_vifs))
+				return -EBUSY;
+
+			new_ctx = ieee80211_alloc_chanctx(local, chandef, mode);
+			if (!new_ctx)
+				return -ENOMEM;
+
+			new_ctx->replace_ctx = curr_ctx;
+			new_ctx->replace_state =
+					IEEE80211_CHANCTX_REPLACES_OTHER;
+
+			curr_ctx->replace_ctx = new_ctx;
+			curr_ctx->replace_state =
+					IEEE80211_CHANCTX_WILL_BE_REPLACED;
+
+			list_add_rcu(&new_ctx->list, &local->chanctx_list);
 		}
 	}
 
@@ -958,82 +1051,567 @@ int ieee80211_vif_reserve_chanctx(struct ieee80211_sub_if_data *sdata,
 	sdata->reserved_chanctx = new_ctx;
 	sdata->reserved_chandef = *chandef;
 	sdata->reserved_radar_required = radar_required;
-out:
-	mutex_unlock(&local->chanctx_mtx);
-	return ret;
+	sdata->reserved_ready = false;
+
+	return 0;
 }
 
-int ieee80211_vif_use_reserved_context(struct ieee80211_sub_if_data *sdata,
-				       u32 *changed)
+static int
+ieee80211_vif_use_reserved_reassign(struct ieee80211_sub_if_data *sdata)
 {
 	struct ieee80211_local *local = sdata->local;
-	struct ieee80211_chanctx *ctx;
-	struct ieee80211_chanctx *old_ctx;
-	struct ieee80211_chanctx_conf *conf;
-	int ret;
-	u32 tmp_changed = *changed;
-
-	/* TODO: need to recheck if the chandef is usable etc.? */
+	struct ieee80211_vif_chanctx_switch vif_chsw[1] = {};
+	struct ieee80211_chanctx *old_ctx, *new_ctx;
+	const struct cfg80211_chan_def *chandef;
+	u32 changed = 0;
+	int err;
 
 	lockdep_assert_held(&local->mtx);
+	lockdep_assert_held(&local->chanctx_mtx);
 
-	mutex_lock(&local->chanctx_mtx);
+	new_ctx = sdata->reserved_chanctx;
+	old_ctx = ieee80211_vif_get_chanctx(sdata);
 
-	ctx = sdata->reserved_chanctx;
-	if (WARN_ON(!ctx)) {
-		ret = -EINVAL;
-		goto out;
-	}
+	if (WARN_ON(!sdata->reserved_ready))
+		return -EBUSY;
 
-	conf = rcu_dereference_protected(sdata->vif.chanctx_conf,
-					 lockdep_is_held(&local->chanctx_mtx));
-	if (!conf) {
-		ret = -EINVAL;
-		goto out;
+	if (WARN_ON(!new_ctx))
+		return -EINVAL;
+
+	if (WARN_ON(!old_ctx))
+		return -EINVAL;
+
+	if (WARN_ON(new_ctx->replace_state ==
+		    IEEE80211_CHANCTX_REPLACES_OTHER))
+		return -EINVAL;
+
+	chandef = ieee80211_chanctx_non_reserved_chandef(local, new_ctx,
+				&sdata->reserved_chandef);
+	if (WARN_ON(!chandef))
+		return -EINVAL;
+
+	vif_chsw[0].vif = &sdata->vif;
+	vif_chsw[0].old_ctx = &old_ctx->conf;
+	vif_chsw[0].new_ctx = &new_ctx->conf;
+
+	list_del(&sdata->reserved_chanctx_list);
+	sdata->reserved_chanctx = NULL;
+
+	err = drv_switch_vif_chanctx(local, vif_chsw, 1,
+				     CHANCTX_SWMODE_REASSIGN_VIF);
+	if (err) {
+		if (ieee80211_chanctx_refcount(local, new_ctx) == 0)
+			ieee80211_free_chanctx(local, new_ctx);
+
+		return err;
 	}
 
-	old_ctx = container_of(conf, struct ieee80211_chanctx, conf);
+	list_move(&sdata->assigned_chanctx_list, &new_ctx->assigned_vifs);
+	rcu_assign_pointer(sdata->vif.chanctx_conf, &new_ctx->conf);
+
+	if (sdata->vif.type == NL80211_IFTYPE_AP)
+		__ieee80211_vif_copy_chanctx_to_vlans(sdata, false);
+
+	if (ieee80211_chanctx_refcount(local, old_ctx) == 0)
+		ieee80211_free_chanctx(local, old_ctx);
 
 	if (sdata->vif.bss_conf.chandef.width != sdata->reserved_chandef.width)
-		tmp_changed |= BSS_CHANGED_BANDWIDTH;
+		changed = BSS_CHANGED_BANDWIDTH;
 
 	sdata->vif.bss_conf.chandef = sdata->reserved_chandef;
 
-	/* unref our reservation */
-	sdata->reserved_chanctx = NULL;
-	sdata->radar_required = sdata->reserved_radar_required;
+	if (changed)
+		ieee80211_bss_info_change_notify(sdata, changed);
+
+	return err;
+}
+
+static int
+ieee80211_vif_use_reserved_assign(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_local *local = sdata->local;
+	struct ieee80211_chanctx *old_ctx, *new_ctx;
+	const struct cfg80211_chan_def *chandef;
+	int err;
+
+	old_ctx = ieee80211_vif_get_chanctx(sdata);
+	new_ctx = sdata->reserved_chanctx;
+
+	if (WARN_ON(!sdata->reserved_ready))
+		return -EINVAL;
+
+	if (WARN_ON(old_ctx))
+		return -EINVAL;
+
+	if (WARN_ON(!new_ctx))
+		return -EINVAL;
+
+	if (WARN_ON(new_ctx->replace_state ==
+		    IEEE80211_CHANCTX_REPLACES_OTHER))
+		return -EINVAL;
+
+	chandef = ieee80211_chanctx_non_reserved_chandef(local, new_ctx,
+				&sdata->reserved_chandef);
+	if (WARN_ON(!chandef))
+		return -EINVAL;
+
 	list_del(&sdata->reserved_chanctx_list);
+	sdata->reserved_chanctx = NULL;
 
-	if (old_ctx == ctx) {
-		/* This is our own context, just change it */
-		ret = __ieee80211_vif_change_channel(sdata, old_ctx,
-						     &tmp_changed);
-		if (ret)
-			goto out;
-	} else {
-		ret = ieee80211_assign_vif_chanctx(sdata, ctx);
-		if (ieee80211_chanctx_refcount(local, old_ctx) == 0)
-			ieee80211_free_chanctx(local, old_ctx);
-		if (ret) {
-			/* if assign fails refcount stays the same */
-			if (ieee80211_chanctx_refcount(local, ctx) == 0)
-				ieee80211_free_chanctx(local, ctx);
+	err = ieee80211_assign_vif_chanctx(sdata, new_ctx);
+	if (err) {
+		if (ieee80211_chanctx_refcount(local, new_ctx) == 0)
+			ieee80211_free_chanctx(local, new_ctx);
+
+		goto out;
+	}
+
+out:
+	return err;
+}
+
+static bool
+ieee80211_vif_has_in_place_reservation(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_chanctx *old_ctx, *new_ctx;
+
+	lockdep_assert_held(&sdata->local->chanctx_mtx);
+
+	new_ctx = sdata->reserved_chanctx;
+	old_ctx = ieee80211_vif_get_chanctx(sdata);
+
+	if (!old_ctx)
+		return false;
+
+	if (WARN_ON(!new_ctx))
+		return false;
+
+	if (old_ctx->replace_state != IEEE80211_CHANCTX_WILL_BE_REPLACED)
+		return false;
+
+	if (new_ctx->replace_state != IEEE80211_CHANCTX_REPLACES_OTHER)
+		return false;
+
+	return true;
+}
+
+static int ieee80211_chsw_switch_hwconf(struct ieee80211_local *local,
+					struct ieee80211_chanctx *new_ctx)
+{
+	const struct cfg80211_chan_def *chandef;
+
+	lockdep_assert_held(&local->mtx);
+	lockdep_assert_held(&local->chanctx_mtx);
+
+	chandef = ieee80211_chanctx_reserved_chandef(local, new_ctx, NULL);
+	if (WARN_ON(!chandef))
+		return -EINVAL;
+
+	local->hw.conf.radar_enabled = new_ctx->conf.radar_enabled;
+	local->_oper_chandef = *chandef;
+	ieee80211_hw_config(local, 0);
+
+	return 0;
+}
+
+static int ieee80211_chsw_switch_vifs(struct ieee80211_local *local,
+				      int n_vifs)
+{
+	struct ieee80211_vif_chanctx_switch *vif_chsw;
+	struct ieee80211_sub_if_data *sdata;
+	struct ieee80211_chanctx *ctx, *old_ctx;
+	int i, err;
+
+	lockdep_assert_held(&local->mtx);
+	lockdep_assert_held(&local->chanctx_mtx);
+
+	vif_chsw = kzalloc(sizeof(vif_chsw[0]) * n_vifs, GFP_KERNEL);
+	if (!vif_chsw)
+		return -ENOMEM;
+
+	i = 0;
+	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state != IEEE80211_CHANCTX_REPLACES_OTHER)
+			continue;
+
+		if (WARN_ON(!ctx->replace_ctx)) {
+			err = -EINVAL;
 			goto out;
 		}
 
-		if (sdata->vif.type == NL80211_IFTYPE_AP)
-			__ieee80211_vif_copy_chanctx_to_vlans(sdata, false);
+		list_for_each_entry(sdata, &ctx->reserved_vifs,
+				    reserved_chanctx_list) {
+			if (!ieee80211_vif_has_in_place_reservation(
+					sdata))
+				continue;
+
+			old_ctx = ieee80211_vif_get_chanctx(sdata);
+			vif_chsw[i].vif = &sdata->vif;
+			vif_chsw[i].old_ctx = &old_ctx->conf;
+			vif_chsw[i].new_ctx = &ctx->conf;
+
+			i++;
+		}
 	}
 
-	*changed = tmp_changed;
+	err = drv_switch_vif_chanctx(local, vif_chsw, n_vifs,
+				     CHANCTX_SWMODE_SWAP_CONTEXTS);
 
-	ieee80211_recalc_chanctx_chantype(local, ctx);
-	ieee80211_recalc_smps_chanctx(local, ctx);
-	ieee80211_recalc_radar_chanctx(local, ctx);
-	ieee80211_recalc_chanctx_min_def(local, ctx);
 out:
-	mutex_unlock(&local->chanctx_mtx);
-	return ret;
+	kfree(vif_chsw);
+	return err;
+}
+
+static int ieee80211_chsw_switch_ctxs(struct ieee80211_local *local)
+{
+	struct ieee80211_chanctx *ctx;
+	int err;
+
+	lockdep_assert_held(&local->mtx);
+	lockdep_assert_held(&local->chanctx_mtx);
+
+	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state != IEEE80211_CHANCTX_REPLACES_OTHER)
+			continue;
+
+		if (!list_empty(&ctx->replace_ctx->assigned_vifs))
+			continue;
+
+		ieee80211_del_chanctx(local, ctx->replace_ctx);
+		err = ieee80211_add_chanctx(local, ctx);
+		if (err)
+			goto err;
+	}
+
+	return 0;
+
+err:
+	WARN_ON(ieee80211_add_chanctx(local, ctx));
+	list_for_each_entry_continue_reverse(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state != IEEE80211_CHANCTX_REPLACES_OTHER)
+			continue;
+
+		if (!list_empty(&ctx->replace_ctx->assigned_vifs))
+			continue;
+
+		ieee80211_del_chanctx(local, ctx);
+		WARN_ON(ieee80211_add_chanctx(local, ctx->replace_ctx));
+	}
+
+	return err;
+}
+
+int
+ieee80211_vif_use_reserved_switch(struct ieee80211_local *local)
+{
+	struct ieee80211_sub_if_data *sdata, *sdata_tmp;
+	struct ieee80211_chanctx *ctx, *ctx_tmp, *old_ctx;
+	struct ieee80211_chanctx *new_ctx = NULL;
+	int i, err, n_assigned, n_reserved, n_ready;
+	int n_ctx = 0, n_vifs_switch = 0, n_vifs_assign = 0, n_vifs_ctxless = 0;
+
+	lockdep_assert_held(&local->mtx);
+	lockdep_assert_held(&local->chanctx_mtx);
+
+	/*
+	 * If there are 2 independent pairs of channel contexts performing
+	 * cross-switch of their vifs this code will still wait until both are
+	 * ready even though it could be possible to switch one before the
+	 * other is ready.
+	 *
+	 * For practical reasons and code simplicity just do a single huge
+	 * switch.
+	 */
+
+	/*
+	 * Verify if the reservation is still feasible.
+	 *  - if it's not then disconnect
+	 *  - if it is but not all vifs necessary are ready then defer
+	 */
+
+	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state != IEEE80211_CHANCTX_REPLACES_OTHER)
+			continue;
+
+		if (WARN_ON(!ctx->replace_ctx)) {
+			err = -EINVAL;
+			goto err;
+		}
+
+		if (!local->use_chanctx)
+			new_ctx = ctx;
+
+		n_ctx++;
+
+		n_assigned = 0;
+		n_reserved = 0;
+		n_ready = 0;
+
+		list_for_each_entry(sdata, &ctx->replace_ctx->assigned_vifs,
+				    assigned_chanctx_list) {
+			n_assigned++;
+			if (sdata->reserved_chanctx) {
+				n_reserved++;
+				if (sdata->reserved_ready)
+					n_ready++;
+			}
+		}
+
+		if (n_assigned != n_reserved) {
+			if (n_ready == n_reserved) {
+				wiphy_info(local->hw.wiphy,
+					   "channel context reservation cannot be finalized because some interfaces aren't switching\n");
+				err = -EBUSY;
+				goto err;
+			}
+
+			return -EAGAIN;
+		}
+
+		ctx->conf.radar_enabled = false;
+		list_for_each_entry(sdata, &ctx->reserved_vifs,
+				    reserved_chanctx_list) {
+			if (ieee80211_vif_has_in_place_reservation(sdata) &&
+			    !sdata->reserved_ready)
+				return -EAGAIN;
+
+			old_ctx = ieee80211_vif_get_chanctx(sdata);
+			if (old_ctx) {
+				if (old_ctx->replace_state ==
+				    IEEE80211_CHANCTX_WILL_BE_REPLACED)
+					n_vifs_switch++;
+				else
+					n_vifs_assign++;
+			} else {
+				n_vifs_ctxless++;
+			}
+
+			if (sdata->reserved_radar_required)
+				ctx->conf.radar_enabled = true;
+		}
+	}
+
+	if (WARN_ON(n_ctx == 0) ||
+	    WARN_ON(n_vifs_switch == 0 &&
+		    n_vifs_assign == 0 &&
+		    n_vifs_ctxless == 0) ||
+	    WARN_ON(n_ctx > 1 && !local->use_chanctx) ||
+	    WARN_ON(!new_ctx && !local->use_chanctx)) {
+		err = -EINVAL;
+		goto err;
+	}
+
+	/*
+	 * All necessary vifs are ready. Perform the switch now depending on
+	 * reservations and driver capabilities.
+	 */
+
+	if (local->use_chanctx) {
+		if (n_vifs_switch > 0) {
+			err = ieee80211_chsw_switch_vifs(local, n_vifs_switch);
+			if (err)
+				goto err;
+		}
+
+		if (n_vifs_assign > 0 || n_vifs_ctxless > 0) {
+			err = ieee80211_chsw_switch_ctxs(local);
+			if (err)
+				goto err;
+		}
+	} else {
+		err = ieee80211_chsw_switch_hwconf(local, new_ctx);
+		if (err)
+			goto err;
+	}
+
+	/*
+	 * Update all structures, values and pointers to point to new channel
+	 * context(s).
+	 */
+
+	i = 0;
+	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state != IEEE80211_CHANCTX_REPLACES_OTHER)
+			continue;
+
+		if (WARN_ON(!ctx->replace_ctx)) {
+			err = -EINVAL;
+			goto err;
+		}
+
+		list_for_each_entry(sdata, &ctx->reserved_vifs,
+				    reserved_chanctx_list) {
+			u32 changed = 0;
+
+			if (!ieee80211_vif_has_in_place_reservation(sdata))
+				continue;
+
+			rcu_assign_pointer(sdata->vif.chanctx_conf, &ctx->conf);
+
+			if (sdata->vif.type == NL80211_IFTYPE_AP)
+				__ieee80211_vif_copy_chanctx_to_vlans(sdata,
+								      false);
+
+			sdata->radar_required = sdata->reserved_radar_required;
+
+			if (sdata->vif.bss_conf.chandef.width !=
+			    sdata->reserved_chandef.width)
+				changed = BSS_CHANGED_BANDWIDTH;
+
+			sdata->vif.bss_conf.chandef = sdata->reserved_chandef;
+			if (changed)
+				ieee80211_bss_info_change_notify(sdata,
+								 changed);
+
+			ieee80211_recalc_txpower(sdata);
+		}
+
+		ieee80211_recalc_chanctx_chantype(local, ctx);
+		ieee80211_recalc_smps_chanctx(local, ctx);
+		ieee80211_recalc_radar_chanctx(local, ctx);
+		ieee80211_recalc_chanctx_min_def(local, ctx);
+
+		list_for_each_entry_safe(sdata, sdata_tmp, &ctx->reserved_vifs,
+					 reserved_chanctx_list) {
+			if (ieee80211_vif_get_chanctx(sdata) != ctx)
+				continue;
+
+			list_del(&sdata->reserved_chanctx_list);
+			list_move(&sdata->assigned_chanctx_list,
+				  &new_ctx->assigned_vifs);
+			sdata->reserved_chanctx = NULL;
+		}
+
+		/*
+		 * This context might have been a dependency for an already
+		 * ready re-assign reservation interface that was deferred. Do
+		 * not propagate error to the caller though. The in-place
+		 * reservation for originally requested interface has already
+		 * succeeded at this point.
+		 */
+		list_for_each_entry_safe(sdata, sdata_tmp, &ctx->reserved_vifs,
+					 reserved_chanctx_list) {
+			if (WARN_ON(ieee80211_vif_has_in_place_reservation(
+					sdata)))
+				continue;
+
+			if (WARN_ON(sdata->reserved_chanctx != ctx))
+				continue;
+
+			if (!sdata->reserved_ready)
+				continue;
+
+			if (ieee80211_vif_get_chanctx(sdata))
+				err = ieee80211_vif_use_reserved_reassign(
+						sdata);
+			else
+				err = ieee80211_vif_use_reserved_assign(sdata);
+
+			if (err) {
+				sdata_info(sdata,
+					   "failed to finalize (re-)assign reservation (err=%d)\n",
+					   err);
+				ieee80211_vif_unreserve_chanctx(sdata);
+				cfg80211_stop_iface(local->hw.wiphy,
+						    &sdata->wdev,
+						    GFP_KERNEL);
+			}
+		}
+	}
+
+	/*
+	 * Finally free old contexts
+	 */
+
+	list_for_each_entry_safe(ctx, ctx_tmp, &local->chanctx_list, list) {
+		if (ctx->replace_state != IEEE80211_CHANCTX_WILL_BE_REPLACED)
+			continue;
+
+		ctx->replace_ctx->replace_ctx = NULL;
+		ctx->replace_ctx->replace_state =
+				IEEE80211_CHANCTX_REPLACE_NONE;
+
+		list_del_rcu(&ctx->list);
+		kfree_rcu(ctx, rcu_head);
+	}
+
+	return 0;
+
+err:
+	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state != IEEE80211_CHANCTX_REPLACES_OTHER)
+			continue;
+
+		list_for_each_entry_safe(sdata, sdata_tmp, &ctx->reserved_vifs,
+					 reserved_chanctx_list)
+			ieee80211_vif_unreserve_chanctx(sdata);
+	}
+
+	return err;
+}
+
+int ieee80211_vif_use_reserved_context(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_local *local = sdata->local;
+	struct ieee80211_chanctx *new_ctx;
+	struct ieee80211_chanctx *old_ctx;
+	int err;
+
+	lockdep_assert_held(&local->mtx);
+	lockdep_assert_held(&local->chanctx_mtx);
+
+	new_ctx = sdata->reserved_chanctx;
+	old_ctx = ieee80211_vif_get_chanctx(sdata);
+
+	if (WARN_ON(!new_ctx))
+		return -EINVAL;
+
+	if (WARN_ON(new_ctx->replace_state ==
+		    IEEE80211_CHANCTX_WILL_BE_REPLACED))
+		return -EINVAL;
+
+	if (WARN_ON(sdata->reserved_ready))
+		return -EINVAL;
+
+	sdata->reserved_ready = true;
+
+	if (new_ctx->replace_state == IEEE80211_CHANCTX_REPLACE_NONE) {
+		if (old_ctx)
+			err = ieee80211_vif_use_reserved_reassign(sdata);
+		else
+			err = ieee80211_vif_use_reserved_assign(sdata);
+
+		if (err)
+			return err;
+	}
+
+	/*
+	 * In-place reservation may need to be finalized now either if:
+	 *  a) sdata is taking part in the swapping itself and is the last one
+	 *  b) sdata has switched with a re-assign reservation to an existing
+	 *     context readying in-place switching of old_ctx
+	 *
+	 * In case of (b) do not propagate the error up because the requested
+	 * sdata already switched successfully. Just spill an extra warning.
+	 * The ieee80211_vif_use_reserved_switch() already stops all necessary
+	 * interfaces upon failure.
+	 */
+	if ((old_ctx &&
+	     old_ctx->replace_state == IEEE80211_CHANCTX_WILL_BE_REPLACED) ||
+	    new_ctx->replace_state == IEEE80211_CHANCTX_REPLACES_OTHER) {
+		err = ieee80211_vif_use_reserved_switch(local);
+		if (err && err != -EAGAIN) {
+			if (new_ctx->replace_state ==
+			    IEEE80211_CHANCTX_REPLACES_OTHER)
+				return err;
+
+			wiphy_info(local->hw.wiphy,
+				   "depending in-place reservation failed (err=%d)\n",
+				   err);
+		}
+	}
+
+	return 0;
 }
 
 int ieee80211_vif_change_bandwidth(struct ieee80211_sub_if_data *sdata,
@@ -1043,6 +1621,7 @@ int ieee80211_vif_change_bandwidth(struct ieee80211_sub_if_data *sdata,
 	struct ieee80211_local *local = sdata->local;
 	struct ieee80211_chanctx_conf *conf;
 	struct ieee80211_chanctx *ctx;
+	const struct cfg80211_chan_def *compat;
 	int ret;
 
 	if (!cfg80211_chandef_usable(sdata->local->hw.wiphy, chandef,
@@ -1069,11 +1648,33 @@ int ieee80211_vif_change_bandwidth(struct ieee80211_sub_if_data *sdata,
 	}
 
 	ctx = container_of(conf, struct ieee80211_chanctx, conf);
-	if (!cfg80211_chandef_compatible(&conf->def, chandef)) {
+
+	compat = cfg80211_chandef_compatible(&conf->def, chandef);
+	if (!compat) {
 		ret = -EINVAL;
 		goto out;
 	}
 
+	switch (ctx->replace_state) {
+	case IEEE80211_CHANCTX_REPLACE_NONE:
+		if (!ieee80211_chanctx_reserved_chandef(local, ctx, compat)) {
+			ret = -EBUSY;
+			goto out;
+		}
+		break;
+	case IEEE80211_CHANCTX_WILL_BE_REPLACED:
+		/* TODO: Perhaps the bandwith change could be treated as a
+		 * reservation itself? */
+		ret = -EBUSY;
+		goto out;
+	case IEEE80211_CHANCTX_REPLACES_OTHER:
+		/* channel context that is going to replace another channel
+		 * context doesn't really exist and shouldn't be assigned
+		 * anywhere yet */
+		WARN_ON(1);
+		break;
+	}
+
 	sdata->vif.bss_conf.chandef = *chandef;
 
 	ieee80211_recalc_chanctx_chantype(local, ctx);
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index f88bd1659cde..c26955f6c14d 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -701,6 +701,24 @@ enum ieee80211_chanctx_mode {
 	IEEE80211_CHANCTX_EXCLUSIVE
 };
 
+/**
+ * enum ieee80211_chanctx_replace_state - channel context replacement state
+ *
+ * This is used for channel context in-place reservations that require channel
+ * context switch/swap.
+ *
+ * @IEEE80211_CHANCTX_REPLACE_NONE: no replacement is taking place
+ * @IEEE80211_CHANCTX_WILL_BE_REPLACED: this channel context will be replaced
+ *	by a (not yet registered) channel context pointed by %replace_ctx.
+ * @IEEE80211_CHANCTX_REPLACES_OTHER: this (not yet registered) channel context
+ *	replaces an existing channel context pointed to by %replace_ctx.
+ */
+enum ieee80211_chanctx_replace_state {
+	IEEE80211_CHANCTX_REPLACE_NONE,
+	IEEE80211_CHANCTX_WILL_BE_REPLACED,
+	IEEE80211_CHANCTX_REPLACES_OTHER,
+};
+
 struct ieee80211_chanctx {
 	struct list_head list;
 	struct rcu_head rcu_head;
@@ -708,6 +726,9 @@ struct ieee80211_chanctx {
 	struct list_head assigned_vifs;
 	struct list_head reserved_vifs;
 
+	enum ieee80211_chanctx_replace_state replace_state;
+	struct ieee80211_chanctx *replace_ctx;
+
 	enum ieee80211_chanctx_mode mode;
 	bool driver_present;
 
@@ -778,6 +799,7 @@ struct ieee80211_sub_if_data {
 	struct ieee80211_chanctx *reserved_chanctx;
 	struct cfg80211_chan_def reserved_chandef;
 	bool reserved_radar_required;
+	bool reserved_ready;
 
 	/* used to reconfigure hardware SM PS */
 	struct work_struct recalc_smps;
@@ -1820,9 +1842,9 @@ ieee80211_vif_reserve_chanctx(struct ieee80211_sub_if_data *sdata,
 			      enum ieee80211_chanctx_mode mode,
 			      bool radar_required);
 int __must_check
-ieee80211_vif_use_reserved_context(struct ieee80211_sub_if_data *sdata,
-				   u32 *changed);
+ieee80211_vif_use_reserved_context(struct ieee80211_sub_if_data *sdata);
 int ieee80211_vif_unreserve_chanctx(struct ieee80211_sub_if_data *sdata);
+int ieee80211_vif_use_reserved_switch(struct ieee80211_local *local);
 
 int __must_check
 ieee80211_vif_change_bandwidth(struct ieee80211_sub_if_data *sdata,
diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index e31458201278..1b42aa16ec03 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -1698,7 +1698,9 @@ int ieee80211_reconfig(struct ieee80211_local *local)
 	if (local->use_chanctx) {
 		mutex_lock(&local->chanctx_mtx);
 		list_for_each_entry(ctx, &local->chanctx_list, list)
-			WARN_ON(drv_add_chanctx(local, ctx));
+			if (ctx->replace_state !=
+			    IEEE80211_CHANCTX_REPLACES_OTHER)
+				WARN_ON(drv_add_chanctx(local, ctx));
 		mutex_unlock(&local->chanctx_mtx);
 
 		list_for_each_entry(sdata, &local->interfaces, list) {
@@ -2972,6 +2974,8 @@ int ieee80211_check_combinations(struct ieee80211_sub_if_data *sdata,
 		num[iftype] = 1;
 
 	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state == IEEE80211_CHANCTX_WILL_BE_REPLACED)
+			continue;
 		if (ctx->conf.radar_enabled)
 			radar_detect |= BIT(ctx->conf.def.width);
 		if (ctx->mode == IEEE80211_CHANCTX_EXCLUSIVE) {
@@ -3030,6 +3034,9 @@ int ieee80211_max_num_channels(struct ieee80211_local *local)
 	lockdep_assert_held(&local->chanctx_mtx);
 
 	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		if (ctx->replace_state == IEEE80211_CHANCTX_WILL_BE_REPLACED)
+			continue;
+
 		num_different_channels++;
 
 		if (ctx->conf.radar_enabled)