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KVM: protect concurrent make_all_cpus_request

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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>
This commit is contained in:
Marcelo Tosatti 2009-06-17 10:53:47 -03:00 committed by Avi Kivity
parent 29a4b9333b
commit 84261923d3
2 changed files with 4 additions and 0 deletions
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1
include/linux/kvm_host.h
View file

@ -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;

3
virt/kvm/kvm_main.c
View file

@ -746,6 +746,7 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
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 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
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 @@ static struct kvm *kvm_create_vm(void)
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);