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Subject[PATCH v6 28/46] KVM: Use get/put_online_cpus_atomic() to prevent CPU offline from atomic context
Date
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.

Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: kvm@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

virt/kvm/kvm_main.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1cd693a..47f9c30 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -174,7 +174,8 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)

zalloc_cpumask_var(&cpus, GFP_ATOMIC);

- me = get_cpu();
+ get_online_cpus_atomic();
+ me = smp_processor_id();
kvm_for_each_vcpu(i, vcpu, kvm) {
kvm_make_request(req, vcpu);
cpu = vcpu->cpu;
@@ -192,7 +193,7 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
smp_call_function_many(cpus, ack_flush, NULL, 1);
else
called = false;
- put_cpu();
+ put_online_cpus_atomic();
free_cpumask_var(cpus);
return called;
}
@@ -1621,11 +1622,12 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
++vcpu->stat.halt_wakeup;
}

- me = get_cpu();
+ get_online_cpus_atomic();
+ me = smp_processor_id();
if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
if (kvm_arch_vcpu_should_kick(vcpu))
smp_send_reschedule(cpu);
- put_cpu();
+ put_online_cpus_atomic();
}
#endif /* !CONFIG_S390 */



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