[v5,28/45] kvm/vmx: Use get/put_online_cpus_atomic() to prevent CPU offline

Message ID 20130122074018.13822.89637.stgit@srivatsabhat.in.ibm.com
State Not Applicable
Headers show

Commit Message

Srivatsa S. Bhat Jan. 22, 2013, 7:40 a.m.
Once stop_machine() is gone from the CPU offline path, we won't be able to
depend on preempt_disable() or local_irq_disable() to prevent CPUs from
going offline from under us.

Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline,
while invoking from atomic context (in vmx_vcpu_load() to prevent CPUs from
going offline while clearing vmcs).

Reported-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Debugged-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

 arch/x86/kvm/vmx.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)


diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9120ae1..2886ff0 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1557,10 +1557,14 @@  static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u64 phys_addr = __pa(per_cpu(vmxarea, cpu));
-	if (!vmm_exclusive)
+	if (!vmm_exclusive) {
-	else if (vmx->loaded_vmcs->cpu != cpu)
+	} else if (vmx->loaded_vmcs->cpu != cpu) {
+		/* Prevent any CPU from going offline */
+		get_online_cpus_atomic();
+		put_online_cpus_atomic();
+	}
 	if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) {
 		per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;