From 36947254e5f981aeeedab1c7dfa35fc34d330e80 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 18 Feb 2020 13:07:32 -0800 Subject: [PATCH] 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. Tested-by: Christoffer Dall Tested-by: Marc Zyngier Reviewed-by: Peter Xu Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini --- include/linux/kvm_host.h | 2 +- virt/kvm/kvm_main.c | 31 ++++++++++++++++++++++++++++--- 2 files changed, 29 insertions(+), 4 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 20763598b13b..4bd5251b4477 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -431,11 +431,11 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu) */ struct kvm_memslots { u64 generation; - struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM]; /* The mapping table from slot id to the index in memslots[]. */ short id_to_index[KVM_MEM_SLOTS_NUM]; atomic_t lru_slot; int used_slots; + struct kvm_memory_slot memslots[]; }; struct kvm { diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 62e45c64e443..26ccb6c0a461 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -566,7 +566,7 @@ static struct kvm_memslots *kvm_alloc_memslots(void) return NULL; for (i = 0; i < KVM_MEM_SLOTS_NUM; i++) - slots->id_to_index[i] = slots->memslots[i].id = -1; + slots->id_to_index[i] = -1; return slots; } @@ -1078,6 +1078,32 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, return old_memslots; } +/* + * Note, at a minimum, the current number of used slots must be allocated, even + * when deleting a memslot, as we need a complete duplicate of the memslots for + * use when invalidating a memslot prior to deleting/moving the memslot. + */ +static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old, + enum kvm_mr_change change) +{ + struct kvm_memslots *slots; + size_t old_size, new_size; + + old_size = sizeof(struct kvm_memslots) + + (sizeof(struct kvm_memory_slot) * old->used_slots); + + if (change == KVM_MR_CREATE) + new_size = old_size + sizeof(struct kvm_memory_slot); + else + new_size = old_size; + + slots = kvzalloc(new_size, GFP_KERNEL_ACCOUNT); + if (likely(slots)) + memcpy(slots, old, old_size); + + return slots; +} + static int kvm_set_memslot(struct kvm *kvm, const struct kvm_userspace_memory_region *mem, struct kvm_memory_slot *old, @@ -1088,10 +1114,9 @@ static int kvm_set_memslot(struct kvm *kvm, struct kvm_memslots *slots; int r; - slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT); + slots = kvm_dup_memslots(__kvm_memslots(kvm, as_id), change); if (!slots) return -ENOMEM; - memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots)); if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) { /*