vmcs->cpu indicates whether it exists on the target cpu, -1 means the vmcs
does not exist on any vcpu
If vcpu load vmcs with vmcs.cpu = -1, it can be directly added to cpu's percpu
list. The list can be corrupted if the cpu prefetch the vmcs's list before
reading vmcs->cpu. Meanwhile, we should remove vmcs from the list before
making vmcs->vcpu == -1 be visible
Signed-off-by: Xiao Guangrong <xiaoguangr...@linux.vnet.ibm.com>
---
arch/x86/kvm/vmx.c | 17 +++++++++++++++++
1 files changed, 17 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 29e8f42..6056d88 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1002,6 +1002,15 @@ static void __loaded_vmcs_clear(void *arg)
if (per_cpu(current_vmcs, cpu) == loaded_vmcs->vmcs)
per_cpu(current_vmcs, cpu) = NULL;
list_del(&loaded_vmcs->loaded_vmcss_on_cpu_link);
+
+ /*
+ * we should ensure updating loaded_vmcs->loaded_vmcss_on_cpu_link
+ * is before setting loaded_vmcs->vcpu to -1 which is done in
+ * loaded_vmcs_init. Otherwise, other cpu can see vcpu = -1 fist
+ * then adds the vmcs into percpu list before it is deleted.
+ */
+ smp_wmb();
+
loaded_vmcs_init(loaded_vmcs);
}
@@ -1537,6 +1546,14 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
local_irq_disable();
+
+ /*
+ * Read loaded_vmcs->cpu should be before fetching
+ * loaded_vmcs->loaded_vmcss_on_cpu_link.
+ * See the comments in __loaded_vmcs_clear().
+ */
+ smp_rmb();
+
list_add(&vmx->loaded_vmcs->loaded_vmcss_on_cpu_link,
&per_cpu(loaded_vmcss_on_cpu, cpu));
local_irq_enable();
--
1.7.7.6
--
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