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

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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 <christoffer.dall@arm.com>
Tested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2020-02-18 13:07:32 -08:00 committed by Paolo Bonzini
parent 0577d1abe7
commit 36947254e5
2 changed files with 29 additions and 4 deletions
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2
include/linux/kvm_host.h
View File

@ -431,11 +431,11 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
*/ */
struct kvm_memslots { struct kvm_memslots {
u64 generation; u64 generation;
struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
/* The mapping table from slot id to the index in memslots[]. */ /* The mapping table from slot id to the index in memslots[]. */
short id_to_index[KVM_MEM_SLOTS_NUM]; short id_to_index[KVM_MEM_SLOTS_NUM];
atomic_t lru_slot; atomic_t lru_slot;
int used_slots; int used_slots;
struct kvm_memory_slot memslots[];
}; };
struct kvm { struct kvm {

31
virt/kvm/kvm_main.c
View File

@ -566,7 +566,7 @@ static struct kvm_memslots *kvm_alloc_memslots(void)
return NULL; return NULL;
for (i = 0; i < KVM_MEM_SLOTS_NUM; i++) 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; return slots;
} }
@ -1078,6 +1078,32 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
return old_memslots; 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, static int kvm_set_memslot(struct kvm *kvm,
const struct kvm_userspace_memory_region *mem, const struct kvm_userspace_memory_region *mem,
struct kvm_memory_slot *old, struct kvm_memory_slot *old,
@ -1088,10 +1114,9 @@ static int kvm_set_memslot(struct kvm *kvm,
struct kvm_memslots *slots; struct kvm_memslots *slots;
int r; int r;
slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT); slots = kvm_dup_memslots(__kvm_memslots(kvm, as_id), change);
if (!slots) if (!slots)
return -ENOMEM; return -ENOMEM;
memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) { if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
/* /*