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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>
This commit is contained in:
Xiao Guangrong 2012-11-28 20:54:14 +08:00 committed by Marcelo Tosatti
parent e6c7d32172
commit 5a560f8b5e
1 changed files with 17 additions and 0 deletions
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17
arch/x86/kvm/vmx.c
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@ -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();