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KVM: Dynamically size memslot array based on number of used slots

Now that the memslot logic doesn't assume memslots are always non-NULL, dynamically size the array of memslots instead of unconditionally allocating memory for the maximum number of memslots. Note, because a to-be-deleted memslot must first be invalidated, the array size cannot be immediately reduced when deleting a memslot. However, consecutive deletions will realize the memory savings, i.e. a second deletion will trim the entry.

Sean Christopherson committed 6 years ago

Commit 36947251 parent 0577d1a2 files · +29 −4Browse files

Unified · Split

2 files
  1. include/linux/kvm_host.h +1 −1
  2. virt/kvm/kvm_main.c +28 −3
include/linux/kvm_host.h+1−1
@@ -431,11 +431,11 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu) · 430 unmodified lines
431 */431 */
432struct kvm_memslots {432struct kvm_memslots {
433 u64 generation;433 u64 generation;
434 struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
435 /* The mapping table from slot id to the index in memslots[]. */434 /* The mapping table from slot id to the index in memslots[]. */
436 short id_to_index[KVM_MEM_SLOTS_NUM];435 short id_to_index[KVM_MEM_SLOTS_NUM];
437 atomic_t lru_slot;436 atomic_t lru_slot;
438 int used_slots;437 int used_slots;
438 struct kvm_memory_slot memslots[];
439};439};
440 440
441struct kvm {441struct kvm {
virt/kvm/kvm_main.c+28−3
@@ -566,7 +566,7 @@ static struct kvm_memslots *kvm_alloc_memslots(void) · 565 unmodified lines
566 return NULL;566 return NULL;
567 567
568 for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)568 for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
569 slots->id_to_index[i] = slots->memslots[i].id = -1;569 slots->id_to_index[i] = -1;
570 570
571 return slots;571 return slots;
572}572}
@@ -1078,6 +1078,32 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, · 505 unmodified lines
1078 return old_memslots;1078 return old_memslots;
1079}1079}
1080 1080
1081/*
1082 * Note, at a minimum, the current number of used slots must be allocated, even
1083 * when deleting a memslot, as we need a complete duplicate of the memslots for
1084 * use when invalidating a memslot prior to deleting/moving the memslot.
1085 */
1086static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old,
1087 enum kvm_mr_change change)
1088{
1089 struct kvm_memslots *slots;
1090 size_t old_size, new_size;
1091
1092 old_size = sizeof(struct kvm_memslots) +
1093 (sizeof(struct kvm_memory_slot) * old->used_slots);
1094
1095 if (change == KVM_MR_CREATE)
1096 new_size = old_size + sizeof(struct kvm_memory_slot);
1097 else
1098 new_size = old_size;
1099
1100 slots = kvzalloc(new_size, GFP_KERNEL_ACCOUNT);
1101 if (likely(slots))
1102 memcpy(slots, old, old_size);
1103
1104 return slots;
1105}
1106
1081static int kvm_set_memslot(struct kvm *kvm,1107static int kvm_set_memslot(struct kvm *kvm,
1082 const struct kvm_userspace_memory_region *mem,1108 const struct kvm_userspace_memory_region *mem,
1083 struct kvm_memory_slot *old,1109 struct kvm_memory_slot *old,
@@ -1088,10 +1114,9 @@ static int kvm_set_memslot(struct kvm *kvm, · 4 unmodified lines
1088 struct kvm_memslots *slots;1114 struct kvm_memslots *slots;
1089 int r;1115 int r;
1090 1116
1091 slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);1117 slots = kvm_dup_memslots(__kvm_memslots(kvm, as_id), change);
1092 if (!slots)1118 if (!slots)
1093 return -ENOMEM;1119 return -ENOMEM;
1094 memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
1095 1120
1096 if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {1121 if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
1097 /*1122 /*