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Commit 5a560f8b authored by Xiao Guangrong's avatar Xiao Guangrong Committed by Marcelo Tosatti
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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: default avatarXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent e6c7d321

arch/x86/kvm/vmx.c

+17 −0
Original line number Diff line number Diff line
@@ -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();