Re: [Qemu-ppc] [Qemu-devel] [PATCH RFC 1/4] spapr-hcall: take iothread lock during handler call

[Nikunj A Dadhania]

Thomas Huth <address@hidden> writes:

> On 02.09.2016 08:32, Nikunj A Dadhania wrote:
>> Signed-off-by: Nikunj A Dadhania <address@hidden>
>> ---
>>  hw/ppc/spapr_hcall.c | 11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>> 
>> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
>> index e5eca67..daea7a0 100644
>> --- a/hw/ppc/spapr_hcall.c
>> +++ b/hw/ppc/spapr_hcall.c
>> @@ -1075,20 +1075,27 @@ target_ulong spapr_hypercall(PowerPCCPU *cpu, 
>> target_ulong opcode,
>>                               target_ulong *args)
>>  {
>>      sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
>> +    target_ulong ret;
>>  
>>      if ((opcode <= MAX_HCALL_OPCODE)
>>          && ((opcode & 0x3) == 0)) {
>>          spapr_hcall_fn fn = papr_hypercall_table[opcode / 4];
>>  
>>          if (fn) {
>> -            return fn(cpu, spapr, opcode, args);
>> +            qemu_mutex_lock_iothread();
>> +            ret = fn(cpu, spapr, opcode, args);
>> +            qemu_mutex_unlock_iothread();
>> +            return ret;
>>          }
>>      } else if ((opcode >= KVMPPC_HCALL_BASE) &&
>>                 (opcode <= KVMPPC_HCALL_MAX)) {
>>          spapr_hcall_fn fn = kvmppc_hypercall_table[opcode - 
>> KVMPPC_HCALL_BASE];
>>  
>>          if (fn) {
>> -            return fn(cpu, spapr, opcode, args);
>> +            qemu_mutex_lock_iothread();
>> +            ret = fn(cpu, spapr, opcode, args);
>> +            qemu_mutex_unlock_iothread();
>> +            return ret;
>>          }
>>      }
>
> I think this will cause a deadlock when running on KVM since the lock is
> already taken in kvm_arch_handle_exit() - which calls spapr_hypercall()!

Ouch, havent tried this branch yet on KVM :(
Will change to emulation only as suggested in my previous mails.

Regards,
Nikunj