KVM: MMU: Add for_each_shadow_entry(), a simpler alternative to walk_shadow()

Using a for_each loop style removes the need to write callback and nasty
casts.

Implement the walk_shadow() using the for_each_shadow_entry().
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/mmu.c

@@ -150,6 +150,20 @@ struct kvm_shadow_walk {
 		     u64 addr, u64 *spte, int level);
 };
 
+struct kvm_shadow_walk_iterator {
+	u64 addr;
+	hpa_t shadow_addr;
+	int level;
+	u64 *sptep;
+	unsigned index;
+};
+
+#define for_each_shadow_entry(_vcpu, _addr, _walker)    \
+	for (shadow_walk_init(&(_walker), _vcpu, _addr);	\
+	     shadow_walk_okay(&(_walker));			\
+	     shadow_walk_next(&(_walker)))
+
+
 struct kvm_unsync_walk {
 	int (*entry) (struct kvm_mmu_page *sp, struct kvm_unsync_walk *walk);
 };
@@ -1254,33 +1268,48 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 	return sp;
 }
 
+static void shadow_walk_init(struct kvm_shadow_walk_iterator *iterator,
+			     struct kvm_vcpu *vcpu, u64 addr)
+{
+	iterator->addr = addr;
+	iterator->shadow_addr = vcpu->arch.mmu.root_hpa;
+	iterator->level = vcpu->arch.mmu.shadow_root_level;
+	if (iterator->level == PT32E_ROOT_LEVEL) {
+		iterator->shadow_addr
+			= vcpu->arch.mmu.pae_root[(addr >> 30) & 3];
+		iterator->shadow_addr &= PT64_BASE_ADDR_MASK;
+		--iterator->level;
+		if (!iterator->shadow_addr)
+			iterator->level = 0;
+	}
+}
+
+static bool shadow_walk_okay(struct kvm_shadow_walk_iterator *iterator)
+{
+	if (iterator->level < PT_PAGE_TABLE_LEVEL)
+		return false;
+	iterator->index = SHADOW_PT_INDEX(iterator->addr, iterator->level);
+	iterator->sptep	= ((u64 *)__va(iterator->shadow_addr)) + iterator->index;
+	return true;
+}
+
+static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator)
+{
+	iterator->shadow_addr = *iterator->sptep & PT64_BASE_ADDR_MASK;
+	--iterator->level;
+}
+
 static int walk_shadow(struct kvm_shadow_walk *walker,
 		       struct kvm_vcpu *vcpu, u64 addr)
 {
-	hpa_t shadow_addr;
-	int level;
+	struct kvm_shadow_walk_iterator iterator;
 	int r;
-	u64 *sptep;
-	unsigned index;
-
-	shadow_addr = vcpu->arch.mmu.root_hpa;
-	level = vcpu->arch.mmu.shadow_root_level;
-	if (level == PT32E_ROOT_LEVEL) {
-		shadow_addr = vcpu->arch.mmu.pae_root[(addr >> 30) & 3];
-		shadow_addr &= PT64_BASE_ADDR_MASK;
-		if (!shadow_addr)
-			return 1;
-		--level;
-	}
 
-	while (level >= PT_PAGE_TABLE_LEVEL) {
-		index = SHADOW_PT_INDEX(addr, level);
-		sptep = ((u64 *)__va(shadow_addr)) + index;
-		r = walker->entry(walker, vcpu, addr, sptep, level);
+	for_each_shadow_entry(vcpu, addr, iterator) {
+		r = walker->entry(walker, vcpu, addr,
+				  iterator.sptep, iterator.level);
 		if (r)
 			return r;
-		shadow_addr = *sptep & PT64_BASE_ADDR_MASK;
-		--level;
 	}
 	return 0;
 }