KVM: s390: allow only one SIGP STOP (AND STORE STATUS) at a time

A SIGP STOP (AND STORE STATUS) order is complete as soon as the VCPU has been
stopped. This patch makes sure that only one SIGP STOP (AND STORE STATUS) may
be pending at a time (as defined by the architecture). If the action_bits are
still set, a SIGP STOP has been issued but not completed yet. The VCPU is busy
for further SIGP STOP orders.

Also set the CPUSTAT_STOP_INT after the action_bits variable has been modified
(the same order that is used when injecting a KVM_S390_SIGP_STOP from
userspace).

Both changes are needed in preparation for a user space driven VCPU state change
(to avoid race conditions).

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

diff --git a/arch/s390/kvm/sigp.c b/arch/s390/kvm/sigp.c
index 43079a48cc98d7858960e71f4d2f0b0b28ca8708..fd7fb5c5ef5dc0a85dc18b6a5dac50b038f01b6d 100644 (file)
--- a/arch/s390/kvm/sigp.c
+++ b/arch/s390/kvm/sigp.c
@@ -136,6 +136,11 @@ static int __inject_sigp_stop(struct kvm_s390_local_interrupt *li, int action)
        inti->type = KVM_S390_SIGP_STOP;
 
        spin_lock_bh(&li->lock);
+       if (li->action_bits & ACTION_STOP_ON_STOP) {
+               /* another SIGP STOP is pending */
+               rc = SIGP_CC_BUSY;
+               goto out;
+       }
        if ((atomic_read(li->cpuflags) & CPUSTAT_STOPPED)) {
                kfree(inti);
                if ((action & ACTION_STORE_ON_STOP) != 0)
@@ -144,8 +149,8 @@ static int __inject_sigp_stop(struct kvm_s390_local_interrupt *li, int action)
        }
        list_add_tail(&inti->list, &li->list);
        atomic_set(&li->active, 1);
-       atomic_set_mask(CPUSTAT_STOP_INT, li->cpuflags);
        li->action_bits |= action;
+       atomic_set_mask(CPUSTAT_STOP_INT, li->cpuflags);
        if (waitqueue_active(li->wq))
                wake_up_interruptible(li->wq);
 out: