KVM: SVM: fix random segfaults with NPT enabled

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%

Cc: stable@kernel.org
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>

arch/x86/kvm/svm.c

@@ -62,6 +62,7 @@ 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)
 {
@@ -1027,6 +1028,13 @@ static int pf_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 		KVMTRACE_3D(TDP_FAULT, &svm->vcpu, error_code,
 			    (u32)fault_address, (u32)(fault_address >> 32),
 			    handler);
+	/*
+	 * 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);