Re: [Qemu-devel] [PATCH v2] spapr: add "stop-self" RTAS call required to support hot CPU unplug

[Alexander Graf]

On 29.08.2013, at 11:04, Alexey Kardashevskiy wrote:

> On 08/28/2013 09:42 PM, David Gibson wrote:
>> On Wed, Aug 28, 2013 at 07:32:51PM +1000, Alexey Kardashevskiy wrote:
>>> PAPR+ requires two RTAS calls to be supported by the hypervisor in
>>> order to allow hotplugging VCPUs from the guest. The "start-cpu" RTAS
>>> call was already there but "stop-self" was not.
>>> 
>>> This adds the "stop-self" RTAS call.
>>> 
>>> Signed-off-by: Alexey Kardashevskiy <address@hidden>
>>> ---
>>> Changes:
>>> v2:
>>> * exit_request flag change replaced with more correct cpu_exit() call
>>> * fixed commit message, "spapr: support CPU hotplug"
>>> ---
>>> hw/ppc/spapr_rtas.c | 12 ++++++++++++
>>> 1 file changed, 12 insertions(+)
>>> 
>>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>>> index 394ce05..b906294 100644
>>> --- a/hw/ppc/spapr_rtas.c
>>> +++ b/hw/ppc/spapr_rtas.c
>>> @@ -202,6 +202,17 @@ static void rtas_start_cpu(PowerPCCPU *cpu_, 
>>> sPAPREnvironment *spapr,
>>>     rtas_st(rets, 0, -3);
>>> }
>>> 
>>> +static void rtas_stop_self(PowerPCCPU *cpu, sPAPREnvironment *spapr,
>>> +                           uint32_t token, uint32_t nargs,
>>> +                           target_ulong args,
>>> +                           uint32_t nret, target_ulong rets)
>>> +{
>>> +    CPUState *cs = CPU(cpu);
>>> +
>>> +    cs->halted = 1;
>> 
>> Uh.. I think you still need the msr = 0, or an interrupt could wake
>> the cpu up again.
> 
> 
> Tried with KVM and TCG - nothing wakes up the stopped CPU :-/
> After a CPU stopped, the guest calls H_CPPR and disables interrupts on the
> specific CPU (or "server") on the XICS level. And decrementer interrupt
> does not wake up the CPU.

Why not? With TCG it should :).


Alex