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

[Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>]

Greg Kurz <groug@kaod.org> writes:

> On Fri,  2 Sep 2016 12:02:53 +0530
> Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> wrote:
>
>> Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
>> ---
>>  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;
>>          }
>>      }
>>  
>
> This will serialize all hypercalls, even when it is not needed... Isn't that
> too much coarse grain locking ?

You are right, I was thinking to do this only for emulation case, as
this is not needed for hardware acceleration.

Regards
Nikunj