[PATCH v6 29/46] kvm/vmx: Use get/put_online_cpus_atomic() to preventCPU offline

From: Srivatsa S. Bhat
Date: Mon Feb 18 2013 - 07:44:42 EST

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@xxxxxxxxxxxxxxxxxx>
Debugged-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>

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;

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