[PATCH] KVM: MMU: Teach the page table walker to track guest page table gfns

Saving the table gfns removes the need to walk the guest and host page tables
in lockstep.
Signed-off-by: NAvi Kivity <avi@qumranet.com>
Acked-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/kvm/paging_tmpl.h

@@ -52,6 +52,7 @@
  */
 struct guest_walker {
 	int level;
+	gfn_t table_gfn;
 	pt_element_t *table;
 	pt_element_t inherited_ar;
 };
@@ -63,8 +64,8 @@ static void FNAME(init_walker)(struct guest_walker *walker,
 	struct kvm_memory_slot *slot;
 
 	walker->level = vcpu->mmu.root_level;
-	slot = gfn_to_memslot(vcpu->kvm,
-			      (vcpu->cr3 & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT);
+	walker->table_gfn = (vcpu->cr3 & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+	slot = gfn_to_memslot(vcpu->kvm, walker->table_gfn);
 	hpa = safe_gpa_to_hpa(vcpu, vcpu->cr3 & PT64_BASE_ADDR_MASK);
 	walker->table = kmap_atomic(pfn_to_page(hpa >> PAGE_SHIFT), KM_USER0);
 
@@ -133,6 +134,8 @@ static pt_element_t *FNAME(fetch_guest)(struct kvm_vcpu *vcpu,
 			return &walker->table[index];
 		if (walker->level != 3 || is_long_mode(vcpu))
 			walker->inherited_ar &= walker->table[index];
+		walker->table_gfn = (walker->table[index] & PT_BASE_ADDR_MASK)
+			>> PAGE_SHIFT;
 		paddr = safe_gpa_to_hpa(vcpu, walker->table[index] & PT_BASE_ADDR_MASK);
 		kunmap_atomic(walker->table, KM_USER0);
 		walker->table = kmap_atomic(pfn_to_page(paddr >> PAGE_SHIFT),