KVM: Keep memslots in tree-based structures instead of array-based ones

The current memslot code uses a (reverse gfn-ordered) memslot array for
keeping track of them.

Because the memslot array that is currently in use cannot be modified
every memslot management operation (create, delete, move, change flags)
has to make a copy of the whole array so it has a scratch copy to work on.

Strictly speaking, however, it is only necessary to make copy of the
memslot that is being modified, copying all the memslots currently present
is just a limitation of the array-based memslot implementation.

Two memslot sets, however, are still needed so the VM continues to run
on the currently active set while the requested operation is being
performed on the second, currently inactive one.

In order to have two memslot sets, but only one copy of actual memslots
it is necessary to split out the memslot data from the memslot sets.

The memslots themselves should be also kept independent of each other
so they can be individually added or deleted.

These two memslot sets should normally point to the same set of
memslots. They can, however, be desynchronized when performing a
memslot management operation by replacing the memslot to be modified
by its copy.  After the operation is complete, both memslot sets once
again point to the same, common set of memslot data.

This commit implements the aforementioned idea.

For tracking of gfns an ordinary rbtree is used since memslots cannot
overlap in the guest address space and so this data structure is
sufficient for ensuring that lookups are done quickly.

The "last used slot" mini-caches (both per-slot set one and per-vCPU one),
that keep track of the last found-by-gfn memslot, are still present in the
new code.

Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <17c0cf3663b760a0d3753d4ac08c0753e941b811.1638817641.git.maciej.szmigiero@oracle.com>

1 files changed, 11 insertions, 13 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 5044b2a2c0cc..b943a589ee41 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1037,13 +1037,13 @@ static int kvm_s390_vm_start_migration(struct kvm *kvm)
 	struct kvm_memory_slot *ms;
 	struct kvm_memslots *slots;
 	unsigned long ram_pages = 0;
-	int slotnr;
+	int bkt;
 
 	/* migration mode already enabled */
 	if (kvm->arch.migration_mode)
 		return 0;
 	slots = kvm_memslots(kvm);
-	if (!slots || !slots->used_slots)
+	if (!slots || kvm_memslots_empty(slots))
 		return -EINVAL;
 
 	if (!kvm->arch.use_cmma) {
@@ -1051,8 +1051,7 @@ static int kvm_s390_vm_start_migration(struct kvm *kvm)
 		return 0;
 	}
 	/* mark all the pages in active slots as dirty */
-	for (slotnr = 0; slotnr < slots->used_slots; slotnr++) {
-		ms = slots->memslots + slotnr;
+	kvm_for_each_memslot(ms, bkt, slots) {
 		if (!ms->dirty_bitmap)
 			return -EINVAL;
 		/*
@@ -1976,22 +1975,21 @@ static unsigned long kvm_s390_next_dirty_cmma(struct kvm_memslots *slots,
 					      unsigned long cur_gfn)
 {
 	struct kvm_memory_slot *ms = gfn_to_memslot_approx(slots, cur_gfn);
-	int slotidx = ms - slots->memslots;
 	unsigned long ofs = cur_gfn - ms->base_gfn;
+	struct rb_node *mnode = &ms->gfn_node[slots->node_idx];
 
 	if (ms->base_gfn + ms->npages <= cur_gfn) {
-		slotidx--;
+		mnode = rb_next(mnode);
 		/* If we are above the highest slot, wrap around */
-		if (slotidx < 0)
-			slotidx = slots->used_slots - 1;
+		if (!mnode)
+			mnode = rb_first(&slots->gfn_tree);
 
-		ms = slots->memslots + slotidx;
+		ms = container_of(mnode, struct kvm_memory_slot, gfn_node[slots->node_idx]);
 		ofs = 0;
 	}
 	ofs = find_next_bit(kvm_second_dirty_bitmap(ms), ms->npages, ofs);
-	while ((slotidx > 0) && (ofs >= ms->npages)) {
-		slotidx--;
-		ms = slots->memslots + slotidx;
+	while (ofs >= ms->npages && (mnode = rb_next(mnode))) {
+		ms = container_of(mnode, struct kvm_memory_slot, gfn_node[slots->node_idx]);
 		ofs = find_next_bit(kvm_second_dirty_bitmap(ms), ms->npages, 0);
 	}
 	return ms->base_gfn + ofs;
@@ -2004,7 +2002,7 @@ static int kvm_s390_get_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
 	struct kvm_memslots *slots = kvm_memslots(kvm);
 	struct kvm_memory_slot *ms;
 
-	if (unlikely(!slots->used_slots))
+	if (unlikely(kvm_memslots_empty(slots)))
 		return 0;
 
 	cur_gfn = kvm_s390_next_dirty_cmma(slots, args->start_gfn);