KVM: Handle partial pae pdptr

Some guests (Solaris) do not set up all four pdptrs, but leave some invalid.
kvm incorrectly treated these as valid page directories, pinning the
wrong pages and causing general confusion.

Fix by checking the valid bit of a pae pdpte.  This closes sourceforge bug
1698922.
Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/mmu.c

@@ -806,10 +806,12 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 	for (i = 0; i < 4; ++i) {
 		hpa_t root = vcpu->mmu.pae_root[i];
 
+		if (root) {
 			ASSERT(VALID_PAGE(root));
 			root &= PT64_BASE_ADDR_MASK;
 			page = page_header(root);
 			--page->root_count;
+		}
 		vcpu->mmu.pae_root[i] = INVALID_PAGE;
 	}
 	vcpu->mmu.root_hpa = INVALID_PAGE;
@@ -840,9 +842,13 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
 		hpa_t root = vcpu->mmu.pae_root[i];
 
 		ASSERT(!VALID_PAGE(root));
-		if (vcpu->mmu.root_level == PT32E_ROOT_LEVEL)
+		if (vcpu->mmu.root_level == PT32E_ROOT_LEVEL) {
+			if (!is_present_pte(vcpu->pdptrs[i])) {
+				vcpu->mmu.pae_root[i] = 0;
+				continue;
+			}
 			root_gfn = vcpu->pdptrs[i] >> PAGE_SHIFT;
-		else if (vcpu->mmu.root_level == 0)
+		} else if (vcpu->mmu.root_level == 0)
 			root_gfn = 0;
 		page = kvm_mmu_get_page(vcpu, root_gfn, i << 30,
 					PT32_ROOT_LEVEL, !is_paging(vcpu),