KVM: MMU: Calculate correct base gfn for direct non-DIR level

In Document/kvm/mmu.txt:
  gfn:
    Either the guest page table containing the translations shadowed by this
    page, or the base page frame for linear translations. See role.direct.

But in __direct_map(), the base gfn calculation is incorrect,
it does not calculate correctly when level=3 or 4.

Fix by using PT64_LVL_ADDR_MASK() which accounts for all levels correctly.
Reported-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/mmu.c

@@ -2020,7 +2020,10 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
 		}
 
 		if (*iterator.sptep == shadow_trap_nonpresent_pte) {
-			pseudo_gfn = (iterator.addr & PT64_DIR_BASE_ADDR_MASK) >> PAGE_SHIFT;
+			u64 base_addr = iterator.addr;
+
+			base_addr &= PT64_LVL_ADDR_MASK(iterator.level);
+			pseudo_gfn = base_addr >> PAGE_SHIFT;
 			sp = kvm_mmu_get_page(vcpu, pseudo_gfn, iterator.addr,
 					      iterator.level - 1,
 					      1, ACC_ALL, iterator.sptep);