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authorXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>2012-11-28 20:54:14 +0800
committerMarcelo Tosatti <mtosatti@redhat.com>2012-11-29 21:14:46 -0200
commit5a560f8b5ed361c7be783d5a671ea26ca4d6fa01 (patch)
treeec3e4aa913bcdc0f97222f7a9ee4b52104d1ed1f /arch
parente6c7d32172f10b68fa9a3be05aa1231352a52171 (diff)
KVM: VMX: fix memory order between loading vmcs and clearing vmcs
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 <xiaoguangrong@linux.vnet.ibm.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/vmx.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4406374e3b6d..3606154bbc8b 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();