KVM: protect concurrent make_all_cpus_request

make_all_cpus_request contains a race condition which can
trigger false request completed status, as follows:

CPU0                                              CPU1

if (test_and_set_bit(req,&vcpu->requests))
   ....                                        	   if (test_and_set_bit(req,&vcpu->requests))
   ..                                                  return
proceed to smp_call_function_many(wait=1)

Use a spinlock to serialize concurrent CPUs.

Cc: stable@kernel.org
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index aacc5449f586..16713dc672e4 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -125,6 +125,7 @@ struct kvm_kernel_irq_routing_entry {
 struct kvm {
         struct mutex lock; /* protects the vcpus array and APIC accesses */
         spinlock_t mmu_lock;
+        spinlock_t requests_lock;
         struct rw_semaphore slots_lock;
         struct mm_struct *mm; /* userspace tied to this vm */
         int nmemslots;