Re: [Qemu-devel] [Qemu-ppc] [PATCH 4/5] target-ppc: Handle ibm, nmi-register RTAS call

[Aravinda Prasad <aravinda@linux.vnet.ibm.com>]

On Thursday 04 September 2014 06:39 PM, Alexander Graf wrote:
> 
> 
>> Am 04.09.2014 um 10:25 schrieb Aravinda Prasad <aravinda@linux.vnet.ibm.com>:
>>
>>
>>
>>> On Friday 29 August 2014 03:46 AM, Alexander Graf wrote:
>>>
>>>
>>>> On 28.08.14 19:42, Aravinda Prasad wrote:
>>>>
>>>>
>>>>> On Thursday 28 August 2014 02:07 PM, Alexander Graf wrote:
>>>>>
>>>>>
>>>>>> On 28.08.14 08:38, Aravinda Prasad wrote:
>>>>>>
>>>>>>
>>>>>>> On Wednesday 27 August 2014 04:07 PM, Alexander Graf wrote:
>>>>>>>
>>>>>>>
>>>>>>>> On 25.08.14 15:45, Aravinda Prasad wrote:
>>>>>>>> This patch adds FWNMI support in qemu for powerKVM
>>>>>>>> guests by handling the ibm,nmi-register rtas call.
>>>>>>>> Whenever OS issues ibm,nmi-register RTAS call, the
>>>>>>>> machine check notification address is saved and the
>>>>>>>> machine check interrupt vector 0x200 is patched to
>>>>>>>> issue a private hcall.
>>>>>>>>
>>>>>>>> Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
>>>>>>>> ---
>>>>>>>> hw/ppc/spapr_rtas.c    |   91 ++++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>>> include/hw/ppc/spapr.h |    8 ++++
>>>>>>>> 2 files changed, 98 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>>>>>>>> index 02ddbf9..1135d2b 100644
>>>>>>>> --- a/hw/ppc/spapr_rtas.c
>>>>>>>> +++ b/hw/ppc/spapr_rtas.c
>>>>>>>> @@ -277,6 +277,91 @@ static void rtas_ibm_set_system_parameter(PowerPCCPU *cpu,
>>>>>>>>     rtas_st(rets, 0, ret);
>>>>>>>> }
>>>>>>>>
>>>>>>>> +static void rtas_ibm_nmi_register(PowerPCCPU *cpu,
>>>>>>>> +                                  sPAPREnvironment *spapr,
>>>>>>>> +                                  uint32_t token, uint32_t nargs,
>>>>>>>> +                                  target_ulong args,
>>>>>>>> +                                  uint32_t nret, target_ulong rets)
>>>>>>>> +{
>>>>>>>> +    int i;
>>>>>>>> +    uint32_t branch_inst = 0x48000002;
>>>>>>>> +    target_ulong guest_machine_check_addr;
>>>>>>>> +    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
>>>>>>>> +    /*
>>>>>>>> +     * Trampoline saves r3 in sprg2 and issues private hcall
>>>>>>>> +     * to request qemu to build error log. QEMU builds the
>>>>>>>> +     * error log, copies to rtas-blob and returns the address.
>>>>>>>> +     * The initial 16 bytes in rtas-blob consists of saved srr0
>>>>>>>> +     * and srr1 which we restore and pass on the actual error
>>>>>>>> +     * log address to OS handled mcachine check notification
>>>>>>>> +     * routine
>>>>>>>> +     */
>>>>>>>> +    uint32_t trampoline[] = {
>>>>>>>> +        0x7c7243a6,    /* mtspr   SPRN_SPRG2,r3 */
>>>>>>>> +        0x38600000,    /* li      r3,0   */
>>>>>>>> +        /* 0xf004 is the KVMPPC_H_REPORT_ERR private HCALL */
>>>>>>>> +        0x6063f004,    /* ori     r3,r3,f004  */
>>>>>>>> +        /* Issue H_CALL */
>>>>>>>> +        0x44000022,    /*  sc      1     */
>>>>>>>
>>>>>>> So up to here we're saving r3 in SPRG2 (how do we know that we can
>>>>>>> clobber it?) and call our special hypercall.
>>>>>>>
>>>>>>> But what does all the cruft below here do?
>>>>>>
>>>>>> The saved r3 in SPRG2 is consumed in KVMPPC_H_REPORT_ERR hcall, hence we
>>>>>> can clobber SPRG2 after hcall returns. I have included a comment in
>>>>>> patch 3/5 while building error log. I think better I add one here as well.
>>>>>>
>>>>>>>
>>>>>>>> +        0x7c9243a6,    /* mtspr r4 sprg2 */
>>>>>>>
>>>>>>> Apart from th fact that your order is wrong, this destroys the value of
>>>>>>> r3 that we saved above again.
>>>>>>
>>>>>> SPRG2 is saved inside hcall and hence we don't need SPRG2 further after
>>>>>> KVMPPC_H_REPORT_ERR hcall returns.
>>>>>>
>>>>>>>
>>>>>>>> +        0xe8830000,    /* ld r4, 0(r3) */
>>>>>>>> +        0x7c9a03a6,    /* mtspr r4, srr0 */
>>>>>>>> +        0xe8830008,    /* ld r4, 8(r3) */
>>>>>>>> +        0x7c9b03a6,    /* mtspr r4, srr1 */
>>>>>>>
>>>>>>> Can't we just set srr0 and srr1 directly?
>>>>>>
>>>>>> I checked for instructions in ISA which set srr0/1 directly given an
>>>>>> address, but could not find any such instructions.
>>>>>
>>>>> I mean from QEMU :).
>>>>
>>>> srr0 and srr1, which are properly set when 0x200 is invoked, are
>>>> clobbered when we return from KVMPPC_H_REPORT_ERR hcall. I think they
>>>> are modified before issuing rfid (I can see them getting clobbered from
>>>> QEMU monitor). However when we jump to OS registered machine check
>>>> routine srr0 and srr1 should reflect the value they had when 0x200 was
>>>> invoked.
>>>>
>>>> Hence srr0 and srr1 are saved in hcall and restored when we return from
>>>> hcall. Also we don't have enough scratch registers available to save
>>>> these before invoking hcall from 0x200.
>>>>
>>>> Or am I missing other ways to do this from QEMU?
>>>
>>> If you just do
>>>
>>> cpu_synchronize_state() and then change env->spr[SPRN_SRR0/1] inside
>>> your hypercall handler that should also change the value when you return
>>> from the hcall.
>>
>> I tried cpu_synchronize_state(), however, srr0 and srr1 are still clobbered.
>>
>> Just before I issue hcall from 0x200 I see the following values from
>> QEMU monitor:
>>
>> SRR0 d000000000f40264  SRR1 8000000000209033
>>
>> Inside hcall, I call cpu_synchronize_state(). As soon as I return from
>> hcall I see:
>>
>> SRR0 0000000000000214  SRR1 8000000000001001
>>
>> I see SRR0 is now set to nip in 0x200 and SRR1 to msr value. I think it
>> is reset during returning from hcall before executing rfid.
>>
>> So I think I still need to explicitly save/restore srr0 and srr1 across
>> hcall.
> 
> Please paste the diff that you did to enable use of cpu_synchronize_state().

@@ -668,20 +668,22 @@ static target_ulong h_rtas_update(PowerP
     return 0;
 }

 static target_ulong h_report_mc_err(PowerPCCPU *cpu, sPAPREnvironment
*spapr,
                            target_ulong opcode, target_ulong *args)
 {
     struct rtas_mc_log mc_log;
     CPUPPCState *env = &cpu->env;
     PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);

+    cpu_synchronize_state(CPU(ppc_env_get_cpu(env)));
+
     /*
      * We save the original r3 register in SPRG2 in 0x200 vector,
      * which is patched during call to ibm.nmi-register. Original
      * r3 is required to be included in error log
      */
     mc_log.r3 = env->spr[SPR_SPRG2];

     /*
      * SRR0 and SRR1, containing nip and msr at the time of exception,
      * are clobbered when we return from this hcall. Hence they



> 
> Alex
> 
>>
>>>
>>>
>>> Alex
>>
>> -- 
>> Regards,
>> Aravinda
>>
> 

-- 
Regards,
Aravinda