Commit 36947254 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

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: default avatarChristoffer Dall <christoffer.dall@arm.com>
Tested-by: default avatarMarc Zyngier <maz@kernel.org>
Reviewed-by: default avatarPeter Xu <peterx@redhat.com>
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 0577d1ab

include/linux/kvm_host.h

+1 −1
Original line number Diff line number Diff line
@@ -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 {

virt/kvm/kvm_main.c

+28 −3
Original line number Diff line number Diff line
@@ -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) {

		/*

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