Commit 163da372 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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KVM: Clean up local variable usage in __kvm_set_memory_region() 



Clean up __kvm_set_memory_region() to achieve several goals:

  - Remove local variables that serve no real purpose
  - Improve the readability of the code
  - Better show the relationship between the 'old' and 'new' memslot
  - Prepare for dynamically sizing memslots
  - Document subtle gotchas (via comments)

Note, using 'tmp' to hold the initial memslot is not strictly necessary
at this juncture, e.g. 'old' could be directly copied from
id_to_memslot(), but keep the pointer usage as id_to_memslot() will be
able to return a NULL pointer once memslots are dynamically sized.

Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent e96c81ee

virt/kvm/kvm_main.c

+26 −24
Original line number Diff line number Diff line
@@ -1071,13 +1071,11 @@ static int kvm_delete_memslot(struct kvm *kvm, 
int __kvm_set_memory_region(struct kvm *kvm,

			    const struct kvm_userspace_memory_region *mem)

{

	int r;

	gfn_t base_gfn;

	unsigned long npages;

	struct kvm_memory_slot *slot;

	struct kvm_memory_slot old, new;

	int as_id, id;

	struct kvm_memory_slot *tmp;

	enum kvm_mr_change change;

	int as_id, id;

	int r;



	r = check_memory_region_flags(mem);

	if (r)
@@ -1102,54 +1100,58 @@ int __kvm_set_memory_region(struct kvm *kvm, 
	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)

		return -EINVAL;



	slot = id_to_memslot(__kvm_memslots(kvm, as_id), id);

	base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;

	npages = mem->memory_size >> PAGE_SHIFT;



	if (npages > KVM_MEM_MAX_NR_PAGES)

		return -EINVAL;



	/*

	 * Make a full copy of the old memslot, the pointer will become stale

	 * when the memslots are re-sorted by update_memslots(), and the old

	 * memslot needs to be referenced after calling update_memslots(), e.g.

	 * to free its resources and for arch specific behavior.

	 * to free its resources and for arch specific behavior.  Kill @tmp

	 * after making a copy to deter potentially dangerous usage.

	 */

	old = *slot;

	tmp = id_to_memslot(__kvm_memslots(kvm, as_id), id);

	old = *tmp;

	tmp = NULL;



	if (!mem->memory_size)

		return kvm_delete_memslot(kvm, mem, &old, as_id);



	new = old;



	new.id = id;

	new.base_gfn = base_gfn;

	new.npages = npages;

	new.base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;

	new.npages = mem->memory_size >> PAGE_SHIFT;

	new.flags = mem->flags;

	new.userspace_addr = mem->userspace_addr;



	if (new.npages > KVM_MEM_MAX_NR_PAGES)

		return -EINVAL;



	if (!old.npages) {

		change = KVM_MR_CREATE;

		new.dirty_bitmap = NULL;

		memset(&new.arch, 0, sizeof(new.arch));

	} else { /* Modify an existing slot. */

		if ((new.userspace_addr != old.userspace_addr) ||

		    (npages != old.npages) ||

		    (new.npages != old.npages) ||

		    ((new.flags ^ old.flags) & KVM_MEM_READONLY))

			return -EINVAL;



		if (base_gfn != old.base_gfn)

		if (new.base_gfn != old.base_gfn)

			change = KVM_MR_MOVE;

		else if (new.flags != old.flags)

			change = KVM_MR_FLAGS_ONLY;

		else /* Nothing to change. */

			return 0;



		/* Copy dirty_bitmap and arch from the current memslot. */

		new.dirty_bitmap = old.dirty_bitmap;

		memcpy(&new.arch, &old.arch, sizeof(new.arch));

	}



	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {

		/* Check for overlaps */

		kvm_for_each_memslot(slot, __kvm_memslots(kvm, as_id)) {

			if (slot->id == id)

		kvm_for_each_memslot(tmp, __kvm_memslots(kvm, as_id)) {

			if (tmp->id == id)

				continue;

			if (!((base_gfn + npages <= slot->base_gfn) ||

			      (base_gfn >= slot->base_gfn + slot->npages)))

			if (!((new.base_gfn + new.npages <= tmp->base_gfn) ||

			      (new.base_gfn >= tmp->base_gfn + tmp->npages)))

				return -EEXIST;

		}

	}

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