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

[Greg Kurz <groug@kaod.org>]

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 ?

Cheers.

--
Greg