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>
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index aacc544..16713dc 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -125,6 +125,7 @@
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;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 013a5b3..2884baf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -746,6 +746,7 @@
cpumask_clear(cpus);
me = get_cpu();
+ spin_lock(&kvm->requests_lock);
for (i = 0; i < KVM_MAX_VCPUS; ++i) {
vcpu = kvm->vcpus[i];
if (!vcpu)
@@ -762,6 +763,7 @@
smp_call_function_many(cpus, ack_flush, NULL, 1);
else
called = false;
+ spin_unlock(&kvm->requests_lock);
put_cpu();
free_cpumask_var(cpus);
return called;
@@ -982,6 +984,7 @@
kvm->mm = current->mm;
atomic_inc(&kvm->mm->mm_count);
spin_lock_init(&kvm->mmu_lock);
+ spin_lock_init(&kvm->requests_lock);
kvm_io_bus_init(&kvm->pio_bus);
mutex_init(&kvm->lock);
kvm_io_bus_init(&kvm->mmio_bus);
