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s390x/kvm: Fix potential deadlock in sigp handling 

If two VCPUs exit at the same time and target each other
with a sigp, both could run into a deadlock as run_on_cpu
on CPU0 will free the BQL when starting the CPU1 target routine.
CPU1 will run its sigp initiater for CPU0 before handling
the run_on_cpu requests, thus resulting in a dead lock.

As all qemu SIGPs are slow path anway we can use a big sigp
lock and allow only one SIGP for the guest at a time. We will
return condition code 2 (BUSY) on contention to the guest.

Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
This commit is contained in:
Christian Borntraeger 2016-09-19 13:39:42 +02:00
parent bfcec59a23
commit f9530c3242
1 changed files with 11 additions and 0 deletions
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11
target-s390x/kvm.c
View File

@ -132,6 +132,8 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
KVM_CAP_LAST_INFO
};
static QemuMutex qemu_sigp_mutex;
static int cap_sync_regs;
static int cap_async_pf;
static int cap_mem_op;
@ -287,6 +289,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
}
}
qemu_mutex_init(&qemu_sigp_mutex);
return 0;
}
@ -1774,6 +1778,11 @@ static int handle_sigp(S390CPU *cpu, struct kvm_run *run, uint8_t ipa1)
status_reg = &env->regs[r1];
param = (r1 % 2) ? env->regs[r1] : env->regs[r1 + 1];
if (qemu_mutex_trylock(&qemu_sigp_mutex)) {
ret = SIGP_CC_BUSY;
goto out;
}
switch (order) {
case SIGP_SET_ARCH:
ret = sigp_set_architecture(cpu, param, status_reg);
@ -1783,7 +1792,9 @@ static int handle_sigp(S390CPU *cpu, struct kvm_run *run, uint8_t ipa1)
dst_cpu = s390_cpu_addr2state(env->regs[r3]);
ret = handle_sigp_single_dst(dst_cpu, order, param, status_reg);
}
qemu_mutex_unlock(&qemu_sigp_mutex);
out:
trace_kvm_sigp_finished(order, CPU(cpu)->cpu_index,
dst_cpu ? CPU(dst_cpu)->cpu_index : -1, ret);