KVM: x86/mmu: Set the C-bit in the PDPTRs and LM pseudo-PDPTRs

Set the C-bit in SPTEs that are set outside of the normal MMU flows,
specifically the PDPDTRs and the handful of special cased "LM root"
entries, all of which are shadow paging only.

Note, the direct-mapped-root PDPTR handling is needed for the scenario
where paging is disabled in the guest, in which case KVM uses a direct
mapped MMU even though TDP is disabled.

Fixes: d0ec49d4 ("kvm/x86/svm: Support Secure Memory Encryption within KVM")
Cc: stable@vger.kernel.org
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210305011101.3597423-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -3261,7 +3261,8 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
 
 			root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT),
 					      i << 30, PT32_ROOT_LEVEL, true);
-			mmu->pae_root[i] = root | PT_PRESENT_MASK;
+			mmu->pae_root[i] = root | PT_PRESENT_MASK |
+					   shadow_me_mask;
 		}
 		mmu->root_hpa = __pa(mmu->pae_root);
 	} else
@@ -3314,7 +3315,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
 	 * or a PAE 3-level page table. In either case we need to be aware that
 	 * the shadow page table may be a PAE or a long mode page table.
 	 */
-	pm_mask = PT_PRESENT_MASK;
+	pm_mask = PT_PRESENT_MASK | shadow_me_mask;
 	if (mmu->shadow_root_level == PT64_ROOT_4LEVEL) {
 		pm_mask |= PT_ACCESSED_MASK | PT_WRITABLE_MASK | PT_USER_MASK;