KVM: x86: avoid uninitialized variable warning

This does not show up on all compiler versions, so it sneaked into the
first 4.3 pull request.  The fix is to mimic the logic of the "print
sptes" loop in the "fill array" loop.  Then leaf and root can be
both initialized unconditionally.

Note that "leaf" now points to the first unused element of the array,
not the last filled element.
Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -3309,13 +3309,14 @@ walk_shadow_page_get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
 
 	walk_shadow_page_lockless_begin(vcpu);
 
-	for (shadow_walk_init(&iterator, vcpu, addr), root = iterator.level;
+	for (shadow_walk_init(&iterator, vcpu, addr),
+		 leaf = root = iterator.level;
 	     shadow_walk_okay(&iterator);
 	     __shadow_walk_next(&iterator, spte)) {
-		leaf = iterator.level;
 		spte = mmu_spte_get_lockless(iterator.sptep);
 
 		sptes[leaf - 1] = spte;
+		leaf--;
 
 		if (!is_shadow_present_pte(spte))
 			break;
@@ -3329,7 +3330,7 @@ walk_shadow_page_get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
 	if (reserved) {
 		pr_err("%s: detect reserved bits on spte, addr 0x%llx, dump hierarchy:\n",
 		       __func__, addr);
-		while (root >= leaf) {
+		while (root > leaf) {
 			pr_err("------ spte 0x%llx level %d.\n",
 			       sptes[root - 1], root);
 			root--;