[PATCH] KVM: SVM: fix random segfaults with NPT enabled

Joerg Rodel
2008-08-27T12:19:09Z

From: Joerg Roedel <joerg.roedel@amd.com>

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>
---
arch/x86/kvm/svm.c | 10 +++++++++-
1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 2d5aed4..980f140 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -59,6 +59,7 @@ 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)
{
@@ -1004,10 +1005,17 @@ static int pf_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
KVMTRACE_3D(PAGE_FAULT, &svm->vcpu, error_code,
(u32)fault_address, (u32)(fault_address >> 32),
handler);
- else
+ else {
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
+ */
+ svm_flush_tlb(&svm->vcpu);
+ }

if (event_injection)
kvm_mmu_unprotect_page_virt(&svm->vcpu, fault_address);
--
1.5.3.7