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KVM: Clean up local variable usage in __kvm_set_memory_region()

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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: 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 13:07:28 -08:00 committed by Paolo Bonzini
parent e96c81ee89
commit 163da372de
1 changed files with 26 additions and 24 deletions
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50
virt/kvm/kvm_main.c
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@ -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;
}
}