KVM: nVMX: Flush TLB entries tagged by dest EPTP on L1<->L2 transitions

Liran Alon · bonzini · commit 1438921c6dc1 · 2018-10-13T12:00:53.000+02:00
If L1 and L2 share VPID (because L1 don't use VPID or we haven't allocated
a vpid02), we need to flush TLB on L1&lt;-&gt;L2 transitions.

Before this patch, this TLB flushing was done by vmx_flush_tlb().
If L0 use EPT, this will translate into INVEPT(active_eptp);
However, if L1 use EPT, in L1-&gt;L2 VMEntry, active EPTP is EPTP01 but
TLB entries populated by L2 are tagged with EPTP02.
Therefore we should delay vmx_flush_tlb() until active_eptp is EPTP02.

To achieve this, instead of directly calling vmx_flush_tlb() we request
it to be called by KVM_REQ_TLB_FLUSH which is evaluated after
KVM_REQ_LOAD_CR3 which sets the active_eptp to EPTP02 as required.

Similarly, on L2-&gt;L1 VMExit, active EPTP is EPTP02 but TLB entries
populated by L1 are tagged with EPTP01 and therefore we should delay
vmx_flush_tlb() until active_eptp is EPTP01.

Reviewed-by: Mihai Carabas &lt;mihai.carabas@oracle.com&gt;
Reviewed-by: Darren Kenny &lt;darren.kenny@oracle.com&gt;
Reviewed-by: Nikita Leshenko &lt;nikita.leshchenko@oracle.com&gt;
Signed-off-by: Liran Alon &lt;liran.alon@oracle.com&gt;
Signed-off-by: Paolo Bonzini &lt;pbonzini@redhat.com&gt;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
@@ -12290,7 +12290,15 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 				__vmx_flush_tlb(vcpu, vmx->nested.vpid02, true);
 			}
 		} else {
-			vmx_flush_tlb(vcpu, true);
+			/*
+			 * If L1 use EPT, then L0 needs to execute INVEPT on
+			 * EPTP02 instead of EPTP01. Therefore, delay TLB
+			 * flush until vmcs02->eptp is fully updated by
+			 * KVM_REQ_LOAD_CR3. Note that this assumes
+			 * KVM_REQ_TLB_FLUSH is evaluated after
+			 * KVM_REQ_LOAD_CR3 in vcpu_enter_guest().
+			 */
+			kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
 		}
 	}
 
@@ -13188,10 +13196,14 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
 	 * Therefore, flush TLB only in case vmcs01 uses VPID and
 	 * vmcs12 don't use VPID as in this case L1 & L2 TLB entries
 	 * are both tagged with vmx->vpid.
+	 *
+	 * If vmcs12 uses EPT, we need to execute this flush on EPTP01
+	 * and therefore we request the TLB flush to happen only after VMCS EPTP
+	 * has been set by KVM_REQ_LOAD_CR3.
 	 */
 	if (enable_vpid &&
 	    !(nested_cpu_has_vpid(vmcs12) && to_vmx(vcpu)->nested.vpid02)) {
-		vmx_flush_tlb(vcpu, true);
+		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
 	}
 
 	vmcs_write32(GUEST_SYSENTER_CS, vmcs12->host_ia32_sysenter_cs);
