diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 364067f811f7..c00eaf2889fb 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1978,6 +1978,10 @@ struct drm_i915_private {
 		struct i915_gt_timelines {
 			struct mutex mutex; /* protects list, tainted by GPU */
 			struct list_head list;
+
+			/* Pack multiple timelines' seqnos into the same page */
+			spinlock_t hwsp_lock;
+			struct list_head hwsp_free_list;
 		} timelines;
 
 		struct list_head active_rings;
diff --git a/drivers/gpu/drm/i915/i915_timeline.c b/drivers/gpu/drm/i915/i915_timeline.c
index 8d5792311a8f..69ee33dfa340 100644
--- a/drivers/gpu/drm/i915/i915_timeline.c
+++ b/drivers/gpu/drm/i915/i915_timeline.c
@@ -9,6 +9,12 @@
 #include "i915_timeline.h"
 #include "i915_syncmap.h"
 
+struct i915_timeline_hwsp {
+	struct i915_vma *vma;
+	struct list_head free_link;
+	u64 free_bitmap;
+};
+
 static struct i915_vma *__hwsp_alloc(struct drm_i915_private *i915)
 {
 	struct drm_i915_gem_object *obj;
@@ -27,28 +33,92 @@ static struct i915_vma *__hwsp_alloc(struct drm_i915_private *i915)
 	return vma;
 }
 
-static int hwsp_alloc(struct i915_timeline *timeline)
+static struct i915_vma *
+hwsp_alloc(struct i915_timeline *timeline, int *offset)
 {
-	struct i915_vma *vma;
+	struct drm_i915_private *i915 = timeline->i915;
+	struct i915_gt_timelines *gt = &i915->gt.timelines;
+	struct i915_timeline_hwsp *hwsp;
+	int cacheline;
 
-	vma = __hwsp_alloc(timeline->i915);
-	if (IS_ERR(vma))
-		return PTR_ERR(vma);
+	BUILD_BUG_ON(BITS_PER_TYPE(u64) * CACHELINE_BYTES > PAGE_SIZE);
 
-	timeline->hwsp_ggtt = vma;
-	timeline->hwsp_offset = 0;
+	spin_lock(&gt->hwsp_lock);
 
-	return 0;
+	/* hwsp_free_list only contains HWSP that have available cachelines */
+	hwsp = list_first_entry_or_null(&gt->hwsp_free_list,
+					typeof(*hwsp), free_link);
+	if (!hwsp) {
+		struct i915_vma *vma;
+
+		spin_unlock(&gt->hwsp_lock);
+
+		hwsp = kmalloc(sizeof(*hwsp), GFP_KERNEL);
+		if (!hwsp)
+			return ERR_PTR(-ENOMEM);
+
+		vma = __hwsp_alloc(i915);
+		if (IS_ERR(vma)) {
+			kfree(hwsp);
+			return vma;
+		}
+
+		vma->private = hwsp;
+		hwsp->vma = vma;
+		hwsp->free_bitmap = ~0ull;
+
+		spin_lock(&gt->hwsp_lock);
+		list_add(&hwsp->free_link, &gt->hwsp_free_list);
+	}
+
+	GEM_BUG_ON(!hwsp->free_bitmap);
+	cacheline = __ffs64(hwsp->free_bitmap);
+	hwsp->free_bitmap &= ~BIT_ULL(cacheline);
+	if (!hwsp->free_bitmap)
+		list_del(&hwsp->free_link);
+
+	spin_unlock(&gt->hwsp_lock);
+
+	GEM_BUG_ON(hwsp->vma->private != hwsp);
+
+	*offset = cacheline * CACHELINE_BYTES;
+	return hwsp->vma;
+}
+
+static void hwsp_free(struct i915_timeline *timeline)
+{
+	struct i915_gt_timelines *gt = &timeline->i915->gt.timelines;
+	struct i915_timeline_hwsp *hwsp;
+
+	hwsp = i915_timeline_hwsp(timeline);
+	if (!hwsp) /* leave global HWSP alone! */
+		return;
+
+	spin_lock(&gt->hwsp_lock);
+
+	/* As a cacheline becomes available, publish the HWSP on the freelist */
+	if (!hwsp->free_bitmap)
+		list_add_tail(&hwsp->free_link, &gt->hwsp_free_list);
+
+	hwsp->free_bitmap |= BIT_ULL(timeline->hwsp_offset / CACHELINE_BYTES);
+
+	/* And if no one is left using it, give the page back to the system */
+	if (hwsp->free_bitmap == ~0ull) {
+		i915_vma_put(hwsp->vma);
+		list_del(&hwsp->free_link);
+		kfree(hwsp);
+	}
+
+	spin_unlock(&gt->hwsp_lock);
 }
 
 int i915_timeline_init(struct drm_i915_private *i915,
 		       struct i915_timeline *timeline,
 		       const char *name,
-		       struct i915_vma *global_hwsp)
+		       struct i915_vma *hwsp)
 {
 	struct i915_gt_timelines *gt = &i915->gt.timelines;
 	void *vaddr;
-	int err;
 
 	/*
 	 * Ideally we want a set of engines on a single leaf as we expect
@@ -64,18 +134,18 @@ int i915_timeline_init(struct drm_i915_private *i915,
 	timeline->name = name;
 	timeline->pin_count = 0;
 
-	if (global_hwsp) {
-		timeline->hwsp_ggtt = i915_vma_get(global_hwsp);
-		timeline->hwsp_offset = I915_GEM_HWS_SEQNO_ADDR;
-	} else {
-		err = hwsp_alloc(timeline);
-		if (err)
-			return err;
+	timeline->hwsp_offset = I915_GEM_HWS_SEQNO_ADDR;
+	if (!hwsp) {
+		hwsp = hwsp_alloc(timeline, &timeline->hwsp_offset);
+		if (IS_ERR(hwsp))
+			return PTR_ERR(hwsp);
 	}
+	timeline->hwsp_ggtt = i915_vma_get(hwsp);
 
-	vaddr = i915_gem_object_pin_map(timeline->hwsp_ggtt->obj, I915_MAP_WB);
+	vaddr = i915_gem_object_pin_map(hwsp->obj, I915_MAP_WB);
 	if (IS_ERR(vaddr)) {
-		i915_vma_put(timeline->hwsp_ggtt);
+		hwsp_free(timeline);
+		i915_vma_put(hwsp);
 		return PTR_ERR(vaddr);
 	}
 
@@ -105,6 +175,9 @@ void i915_timelines_init(struct drm_i915_private *i915)
 	mutex_init(&gt->mutex);
 	INIT_LIST_HEAD(&gt->list);
 
+	spin_lock_init(&gt->hwsp_lock);
+	INIT_LIST_HEAD(&gt->hwsp_free_list);
+
 	/* via i915_gem_wait_for_idle() */
 	i915_gem_shrinker_taints_mutex(i915, &gt->mutex);
 }
@@ -144,12 +217,13 @@ void i915_timeline_fini(struct i915_timeline *timeline)
 	GEM_BUG_ON(timeline->pin_count);
 	GEM_BUG_ON(!list_empty(&timeline->requests));
 
-	i915_syncmap_free(&timeline->sync);
-
 	mutex_lock(&gt->mutex);
 	list_del(&timeline->link);
 	mutex_unlock(&gt->mutex);
 
+	i915_syncmap_free(&timeline->sync);
+	hwsp_free(timeline);
+
 	i915_gem_object_unpin_map(timeline->hwsp_ggtt->obj);
 	i915_vma_put(timeline->hwsp_ggtt);
 }
@@ -226,6 +300,7 @@ void i915_timelines_fini(struct drm_i915_private *i915)
 	struct i915_gt_timelines *gt = &i915->gt.timelines;
 
 	GEM_BUG_ON(!list_empty(&gt->list));
+	GEM_BUG_ON(!list_empty(&gt->hwsp_free_list));
 
 	mutex_destroy(&gt->mutex);
 }
diff --git a/drivers/gpu/drm/i915/i915_timeline.h b/drivers/gpu/drm/i915/i915_timeline.h
index 0c3739d53d79..ab736e2e5707 100644
--- a/drivers/gpu/drm/i915/i915_timeline.h
+++ b/drivers/gpu/drm/i915/i915_timeline.h
@@ -33,6 +33,7 @@
 #include "i915_utils.h"
 
 struct i915_vma;
+struct i915_timeline_hwsp;
 
 struct i915_timeline {
 	u64 fence_context;
diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h
index 5793abe509a2..46eb818ed309 100644
--- a/drivers/gpu/drm/i915/i915_vma.h
+++ b/drivers/gpu/drm/i915/i915_vma.h
@@ -226,6 +226,18 @@ static inline u32 i915_ggtt_pin_bias(struct i915_vma *vma)
 	return i915_vm_to_ggtt(vma->vm)->pin_bias;
 }
 
+/* XXX inline spaghetti */
+static inline struct i915_timeline_hwsp *
+i915_timeline_hwsp(const struct i915_timeline *tl)
+{
+	return tl->hwsp_ggtt->private;
+}
+
+static inline bool i915_timeline_is_global(const struct i915_timeline *tl)
+{
+	return !i915_timeline_hwsp(tl);
+}
+
 static inline struct i915_vma *i915_vma_get(struct i915_vma *vma)
 {
 	i915_gem_object_get(vma->obj);
diff --git a/drivers/gpu/drm/i915/selftests/i915_random.c b/drivers/gpu/drm/i915/selftests/i915_random.c
index 1f415ce47018..716a3f19f030 100644
--- a/drivers/gpu/drm/i915/selftests/i915_random.c
+++ b/drivers/gpu/drm/i915/selftests/i915_random.c
@@ -41,18 +41,37 @@ u64 i915_prandom_u64_state(struct rnd_state *rnd)
 	return x;
 }
 
-void i915_random_reorder(unsigned int *order, unsigned int count,
-			 struct rnd_state *state)
+void i915_prandom_shuffle(void *arr, size_t elsz, size_t count,
+			  struct rnd_state *state)
 {
-	unsigned int i, j;
+	char stack[128];
+
+	if (WARN_ON(elsz > sizeof(stack) || count > U32_MAX))
+		return;
+
+	if (!elsz || !count)
+		return;
+
+	/* Fisher-Yates shuffle courtesy of Knuth */
+	while (--count) {
+		size_t swp;
+
+		swp = i915_prandom_u32_max_state(count + 1, state);
+		if (swp == count)
+			continue;
 
-	for (i = 0; i < count; i++) {
-		BUILD_BUG_ON(sizeof(unsigned int) > sizeof(u32));
-		j = i915_prandom_u32_max_state(count, state);
-		swap(order[i], order[j]);
+		memcpy(stack, arr + count * elsz, elsz);
+		memcpy(arr + count * elsz, arr + swp * elsz, elsz);
+		memcpy(arr + swp * elsz, stack, elsz);
 	}
 }
 
+void i915_random_reorder(unsigned int *order, unsigned int count,
+			 struct rnd_state *state)
+{
+	i915_prandom_shuffle(order, sizeof(*order), count, state);
+}
+
 unsigned int *i915_random_order(unsigned int count, struct rnd_state *state)
 {
 	unsigned int *order, i;
diff --git a/drivers/gpu/drm/i915/selftests/i915_random.h b/drivers/gpu/drm/i915/selftests/i915_random.h
index 7dffedc501ca..8e1ff9c105b6 100644
--- a/drivers/gpu/drm/i915/selftests/i915_random.h
+++ b/drivers/gpu/drm/i915/selftests/i915_random.h
@@ -54,4 +54,7 @@ void i915_random_reorder(unsigned int *order,
 			 unsigned int count,
 			 struct rnd_state *state);
 
+void i915_prandom_shuffle(void *arr, size_t elsz, size_t count,
+			  struct rnd_state *state);
+
 #endif /* !__I915_SELFTESTS_RANDOM_H__ */
diff --git a/drivers/gpu/drm/i915/selftests/i915_timeline.c b/drivers/gpu/drm/i915/selftests/i915_timeline.c
index 1585b614510d..1cecc71fba74 100644
--- a/drivers/gpu/drm/i915/selftests/i915_timeline.c
+++ b/drivers/gpu/drm/i915/selftests/i915_timeline.c
@@ -4,6 +4,8 @@
  * Copyright © 2017-2018 Intel Corporation
  */
 
+#include <linux/prime_numbers.h>
+
 #include "../i915_selftest.h"
 #include "i915_random.h"
 
@@ -11,6 +13,143 @@
 #include "mock_gem_device.h"
 #include "mock_timeline.h"
 
+static struct page *hwsp_page(struct i915_timeline *tl)
+{
+	struct drm_i915_gem_object *obj = tl->hwsp_ggtt->obj;
+
+	GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
+	return sg_page(obj->mm.pages->sgl);
+}
+
+static unsigned long hwsp_cacheline(struct i915_timeline *tl)
+{
+	unsigned long address = (unsigned long)page_address(hwsp_page(tl));
+
+	return (address + tl->hwsp_offset) / CACHELINE_BYTES;
+}
+
+#define CACHELINES_PER_PAGE (PAGE_SIZE / CACHELINE_BYTES)
+
+struct mock_hwsp_freelist {
+	struct drm_i915_private *i915;
+	struct radix_tree_root cachelines;
+	struct i915_timeline **history;
+	unsigned long count, max;
+	struct rnd_state prng;
+};
+
+enum {
+	SHUFFLE = BIT(0),
+};
+
+static void __mock_hwsp_record(struct mock_hwsp_freelist *state,
+			       unsigned int idx,
+			       struct i915_timeline *tl)
+{
+	tl = xchg(&state->history[idx], tl);
+	if (tl) {
+		radix_tree_delete(&state->cachelines, hwsp_cacheline(tl));
+		i915_timeline_put(tl);
+	}
+}
+
+static int __mock_hwsp_timeline(struct mock_hwsp_freelist *state,
+				unsigned int count,
+				unsigned int flags)
+{
+	struct i915_timeline *tl;
+	unsigned int idx;
+
+	while (count--) {
+		unsigned long cacheline;
+		int err;
+
+		tl = i915_timeline_create(state->i915, "mock", NULL);
+		if (IS_ERR(tl))
+			return PTR_ERR(tl);
+
+		cacheline = hwsp_cacheline(tl);
+		err = radix_tree_insert(&state->cachelines, cacheline, tl);
+		if (err) {
+			if (err == -EEXIST) {
+				pr_err("HWSP cacheline %lu already used; duplicate allocation!\n",
+				       cacheline);
+			}
+			i915_timeline_put(tl);
+			return err;
+		}
+
+		idx = state->count++ % state->max;
+		__mock_hwsp_record(state, idx, tl);
+	}
+
+	if (flags & SHUFFLE)
+		i915_prandom_shuffle(state->history,
+				     sizeof(*state->history),
+				     min(state->count, state->max),
+				     &state->prng);
+
+	count = i915_prandom_u32_max_state(min(state->count, state->max),
+					   &state->prng);
+	while (count--) {
+		idx = --state->count % state->max;
+		__mock_hwsp_record(state, idx, NULL);
+	}
+
+	return 0;
+}
+
+static int mock_hwsp_freelist(void *arg)
+{
+	struct mock_hwsp_freelist state;
+	const struct {
+		const char *name;
+		unsigned int flags;
+	} phases[] = {
+		{ "linear", 0 },
+		{ "shuffled", SHUFFLE },
+		{ },
+	}, *p;
+	unsigned int na;
+	int err = 0;
+
+	INIT_RADIX_TREE(&state.cachelines, GFP_KERNEL);
+	state.prng = I915_RND_STATE_INITIALIZER(i915_selftest.random_seed);
+
+	state.i915 = mock_gem_device();
+	if (!state.i915)
+		return -ENOMEM;
+
+	/*
+	 * Create a bunch of timelines and check that their HWSP do not overlap.
+	 * Free some, and try again.
+	 */
+
+	state.max = PAGE_SIZE / sizeof(*state.history);
+	state.count = 0;
+	state.history = kcalloc(state.max, sizeof(*state.history), GFP_KERNEL);
+	if (!state.history) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	for (p = phases; p->name; p++) {
+		pr_debug("%s(%s)\n", __func__, p->name);
+		for_each_prime_number_from(na, 1, 2 * CACHELINES_PER_PAGE) {
+			err = __mock_hwsp_timeline(&state, na, p->flags);
+			if (err)
+				goto out;
+		}
+	}
+
+out:
+	for (na = 0; na < state.max; na++)
+		__mock_hwsp_record(&state, na, NULL);
+	kfree(state.history);
+	drm_dev_put(&state.i915->drm);
+	return err;
+}
+
 struct __igt_sync {
 	const char *name;
 	u32 seqno;
@@ -260,6 +399,7 @@ static int bench_sync(void *arg)
 int i915_timeline_mock_selftests(void)
 {
 	static const struct i915_subtest tests[] = {
+		SUBTEST(mock_hwsp_freelist),
 		SUBTEST(igt_sync),
 		SUBTEST(bench_sync),
 	};
