[PATCH v3 4/8] KVM: Introduce memslots hva tree

["Maciej S. Szmigiero" <mail@maciej.szmigiero.name>]

From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>

The current memslots implementation only allows quick binary search by gfn,
quick lookup by hva is not possible - the implementation has to do a linear
scan of the whole memslots array, even though the operation being performed
might apply just to a single memslot.

This significantly hurts performance of per-hva operations with higher
memslot counts.

Since hva ranges can overlap between memslots an interval tree is needed
for tracking them.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
---
 arch/arm64/kvm/Kconfig   |  1 +
 arch/mips/kvm/Kconfig    |  1 +
 arch/powerpc/kvm/Kconfig |  1 +
 arch/s390/kvm/Kconfig    |  1 +
 arch/x86/kvm/Kconfig     |  1 +
 include/linux/kvm_host.h |  8 ++++++++
 virt/kvm/kvm_main.c      | 43 +++++++++++++++++++++++++++++++++-------
 7 files changed, 49 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 3964acf5451e..f075e9939a2a 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -40,6 +40,7 @@ menuconfig KVM
 	select HAVE_KVM_VCPU_RUN_PID_CHANGE
 	select TASKSTATS
 	select TASK_DELAY_ACCT
+	select INTERVAL_TREE
 	help
 	  Support hosting virtualized guest machines.
 
diff --git a/arch/mips/kvm/Kconfig b/arch/mips/kvm/Kconfig
index a77297480f56..91d197bee9c0 100644
--- a/arch/mips/kvm/Kconfig
+++ b/arch/mips/kvm/Kconfig
@@ -27,6 +27,7 @@ config KVM
 	select KVM_MMIO
 	select MMU_NOTIFIER
 	select SRCU
+	select INTERVAL_TREE
 	help
 	  Support for hosting Guest kernels.
 
diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
index e45644657d49..519d6d3642a5 100644
--- a/arch/powerpc/kvm/Kconfig
+++ b/arch/powerpc/kvm/Kconfig
@@ -26,6 +26,7 @@ config KVM
 	select KVM_VFIO
 	select IRQ_BYPASS_MANAGER
 	select HAVE_KVM_IRQ_BYPASS
+	select INTERVAL_TREE
 
 config KVM_BOOK3S_HANDLER
 	bool
diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index 67a8e770e369..2e84d3922f7c 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -33,6 +33,7 @@ config KVM
 	select HAVE_KVM_NO_POLL
 	select SRCU
 	select KVM_VFIO
+	select INTERVAL_TREE
 	help
 	  Support hosting paravirtualized guest machines using the SIE
 	  virtualization capability on the mainframe. This should work
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index f6b93a35ce14..ee15f7e113c8 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -46,6 +46,7 @@ config KVM
 	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
 	select KVM_VFIO
 	select SRCU
+	select INTERVAL_TREE
 	help
 	  Support hosting fully virtualized guest machines using hardware
 	  virtualization extensions.  You will need a fairly recent
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d3a35646dfd8..f59847b6e9b3 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -27,6 +27,7 @@
 #include <linux/rcuwait.h>
 #include <linux/refcount.h>
 #include <linux/nospec.h>
+#include <linux/interval_tree.h>
 #include <linux/hashtable.h>
 #include <asm/signal.h>
 
@@ -358,6 +359,7 @@ static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
 
 struct kvm_memory_slot {
 	struct hlist_node id_node;
+	struct interval_tree_node hva_node;
 	gfn_t base_gfn;
 	unsigned long npages;
 	unsigned long *dirty_bitmap;
@@ -459,6 +461,7 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
  */
 struct kvm_memslots {
 	u64 generation;
+	struct rb_root_cached hva_tree;
 	/* The mapping table from slot id to the index in memslots[]. */
 	DECLARE_HASHTABLE(id_hash, 7);
 	atomic_t lru_slot;
@@ -679,6 +682,11 @@ static inline struct kvm_memslots *kvm_vcpu_memslots(struct kvm_vcpu *vcpu)
 	return __kvm_memslots(vcpu->kvm, as_id);
 }
 
+#define kvm_for_each_hva_range_memslot(node, slots, start, last)	     \
+	for (node = interval_tree_iter_first(&slots->hva_tree, start, last); \
+	     node;							     \
+	     node = interval_tree_iter_next(node, start, last))	     \
+
 static inline
 struct kvm_memory_slot *id_to_memslot(struct kvm_memslots *slots, int id)
 {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 50f9bc9bb1e0..a55309432c9a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -488,6 +488,9 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 	struct kvm_memslots *slots;
 	int i, idx;
 
+	if (range->end == range->start || WARN_ON(range->end < range->start))
+		return 0;
+
 	/* A null handler is allowed if and only if on_lock() is provided. */
 	if (WARN_ON_ONCE(IS_KVM_NULL_FN(range->on_lock) &&
 			 IS_KVM_NULL_FN(range->handler)))
@@ -507,15 +510,18 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
 	}
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+		struct interval_tree_node *node;
+
 		slots = __kvm_memslots(kvm, i);
-		kvm_for_each_memslot(slot, slots) {
+		kvm_for_each_hva_range_memslot(node, slots,
+					       range->start, range->end - 1) {
 			unsigned long hva_start, hva_end;
 
+			slot = container_of(node, struct kvm_memory_slot,
+					    hva_node);
 			hva_start = max(range->start, slot->userspace_addr);
 			hva_end = min(range->end, slot->userspace_addr +
 						  (slot->npages << PAGE_SHIFT));
-			if (hva_start >= hva_end)
-				continue;
 
 			/*
 			 * To optimize for the likely case where the address
@@ -787,6 +793,7 @@ static struct kvm_memslots *kvm_alloc_memslots(void)
 	if (!slots)
 		return NULL;
 
+	slots->hva_tree = RB_ROOT_CACHED;
 	hash_init(slots->id_hash);
 
 	return slots;
@@ -1113,10 +1120,14 @@ static inline void kvm_memslot_delete(struct kvm_memslots *slots,
 		atomic_set(&slots->lru_slot, 0);
 
 	for (i = dmemslot - mslots; i < slots->used_slots; i++) {
+		interval_tree_remove(&mslots[i].hva_node, &slots->hva_tree);
 		hash_del(&mslots[i].id_node);
+
 		mslots[i] = mslots[i + 1];
+		interval_tree_insert(&mslots[i].hva_node, &slots->hva_tree);
 		hash_add(slots->id_hash, &mslots[i].id_node, mslots[i].id);
 	}
+	interval_tree_remove(&mslots[i].hva_node, &slots->hva_tree);
 	hash_del(&mslots[i].id_node);
 	mslots[i] = *memslot;
 }
@@ -1136,7 +1147,8 @@ static inline int kvm_memslot_insert_back(struct kvm_memslots *slots)
  * itself is not preserved in the array, i.e. not swapped at this time, only
  * its new index into the array is tracked.  Returns the changed memslot's
  * current index into the memslots array.
- * The memslot at the returned index will not be in @slots->id_hash by then.
+ * The memslot at the returned index will not be in @slots->hva_tree or
+ * @slots->id_hash by then.
  * @memslot is a detached struct with desired final data of the changed slot.
  */
 static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
@@ -1154,6 +1166,7 @@ static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
 	 * update_memslots() will unconditionally overwrite and re-add the
 	 * target memslot so it has to be removed here first
 	 */
+	interval_tree_remove(&mmemslot->hva_node, &slots->hva_tree);
 	hash_del(&mmemslot->id_node);
 
 	/*
@@ -1168,8 +1181,11 @@ static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
 		WARN_ON_ONCE(memslot->base_gfn == mslots[i + 1].base_gfn);
 
 		/* Shift the next memslot forward one and update its index. */
+		interval_tree_remove(&mslots[i + 1].hva_node, &slots->hva_tree);
 		hash_del(&mslots[i + 1].id_node);
+
 		mslots[i] = mslots[i + 1];
+		interval_tree_insert(&mslots[i].hva_node, &slots->hva_tree);
 		hash_add(slots->id_hash, &mslots[i].id_node, mslots[i].id);
 	}
 	return i;
@@ -1181,10 +1197,12 @@ static inline int kvm_memslot_move_backward(struct kvm_memslots *slots,
  * is not preserved in the array, i.e. not swapped at this time, only its new
  * index into the array is tracked.  Returns the changed memslot's final index
  * into the memslots array.
- * The memslot at the returned index will not be in @slots->id_hash by then.
+ * The memslot at the returned index will not be in @slots->hva_tree or
+ * @slots->id_hash by then.
  * @memslot is a detached struct with desired final data of the new or
  * changed slot.
- * Assumes that the memslot at @start index is not in @slots->id_hash.
+ * Assumes that the memslot at @start index is not in @slots->hva_tree or
+ * @slots->id_hash.
  */
 static inline int kvm_memslot_move_forward(struct kvm_memslots *slots,
 					   struct kvm_memory_slot *memslot,
@@ -1200,8 +1218,11 @@ static inline int kvm_memslot_move_forward(struct kvm_memslots *slots,
 		WARN_ON_ONCE(memslot->base_gfn == mslots[i - 1].base_gfn);
 
 		/* Shift the next memslot back one and update its index. */
+		interval_tree_remove(&mslots[i - 1].hva_node, &slots->hva_tree);
 		hash_del(&mslots[i - 1].id_node);
+
 		mslots[i] = mslots[i - 1];
+		interval_tree_insert(&mslots[i].hva_node, &slots->hva_tree);
 		hash_add(slots->id_hash, &mslots[i].id_node, mslots[i].id);
 	}
 	return i;
@@ -1274,6 +1295,11 @@ static void update_memslots(struct kvm_memslots *slots,
 		 * its index accordingly.
 		 */
 		slots->memslots[i] = *memslot;
+		slots->memslots[i].hva_node.start = memslot->userspace_addr;
+		slots->memslots[i].hva_node.last = memslot->userspace_addr +
+			(memslot->npages << PAGE_SHIFT) - 1;
+		interval_tree_insert(&slots->memslots[i].hva_node,
+				     &slots->hva_tree);
 		hash_add(slots->id_hash, &slots->memslots[i].id_node,
 			 memslot->id);
 	}
@@ -1355,9 +1381,12 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
 
 	memcpy(slots, old, old_size);
 
+	slots->hva_tree = RB_ROOT_CACHED;
 	hash_init(slots->id_hash);
-	kvm_for_each_memslot(memslot, slots)
+	kvm_for_each_memslot(memslot, slots) {
+		interval_tree_insert(&memslot->hva_node, &slots->hva_tree);
 		hash_add(slots->id_hash, &memslot->id_node, memslot->id);
+	}
 
 	return slots;
 }