[patch 011/108] KVM: protect concurrent make_all_cpus_request

Greg KH
2009-07-01T00:49:55Z

[-- Attachment #1: kvm-protect-concurrent-make_all_cpus_request.patch --]
[-- Type: text/plain, Size: 2124 bytes --]

2.6.30-stable review patch. If anyone has any objections, please let us know.

------------------

From: Marcelo Tosatti <mtosatti@redhat.com>

commit 84261923d3dddb766736023bead6fa07b7e218d5 upstream.

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.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 3 +++
2 files changed, 4 insertions(+)

--- 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;
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -581,6 +581,7 @@ static bool make_all_cpus_request(struct
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)
@@ -597,6 +598,7 @@ static bool make_all_cpus_request(struct
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;
@@ -817,6 +819,7 @@ 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);