KVM: SVM: fix random segfaults with NPT enabled

(cherry picked from commit 44874f84)

This patch introduces a guest TLB flush on every NPF exit in KVM. This fixes
random segfaults and #UD exceptions in the guest seen under some workloads
(e.g. long running compile workloads or tbench). A kernbench run with and
without that fix showed that it has a slowdown lower than 0.5%
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@qumranet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

arch/x86/kvm/svm.c

@@ -60,6 +60,7 @@ static int npt = 1;
 module_param(npt, int, S_IRUGO);
 
 static void kvm_reput_irq(struct vcpu_svm *svm);
+static void svm_flush_tlb(struct kvm_vcpu *vcpu);
 
 static inline struct vcpu_svm *to_svm(struct kvm_vcpu *vcpu)
 {
@@ -1017,6 +1018,15 @@ static int pf_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 
 	fault_address  = svm->vmcb->control.exit_info_2;
 	error_code = svm->vmcb->control.exit_info_1;
+
+	/*
+	 * FIXME: Tis shouldn't be necessary here, but there is a flush
+	 * missing in the MMU code. Until we find this bug, flush the
+	 * complete TLB here on an NPF
+	 */
+	if (npt_enabled)
+		svm_flush_tlb(&svm->vcpu);
+
 	if (event_injection)
 		kvm_mmu_unprotect_page_virt(&svm->vcpu, fault_address);
 	return kvm_mmu_page_fault(&svm->vcpu, fault_address, error_code);