Re: [Qemu-devel] [Qemu-ppc] [PATCH v3 4/4] target-ppc: Handle ibm, nmi-register RTAS call

[Alexander Graf <agraf@suse.de>]

On 05.11.14 12:24, Aravinda Prasad wrote:
> 
> 
> On Wednesday 05 November 2014 04:37 PM, Alexander Graf wrote:
>>
>>
>> On 05.11.14 11:37, Aravinda Prasad wrote:
>>>
>>>
>>> On Wednesday 05 November 2014 02:02 PM, Alexander Graf wrote:
>>>>
>>>>
>>>> On 05.11.14 08:13, 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.
>>>>>
>>>>> This patch also handles the cases when multi-processors
>>>>> experience machine check at or about the same time.
>>>>> As per PAPR, subsequent processors serialize waiting
>>>>> for the first processor to issue the ibm,nmi-interlock call.
>>>>> The second processor retries if the first processor which
>>>>> received a machine check is still reading the error log
>>>>> and is yet to issue ibm,nmi-interlock call.
>>>>>
>>>>> Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
>>>>> ---
>>>>>  hw/ppc/spapr_hcall.c            |   16 +++++++
>>>>>  hw/ppc/spapr_rtas.c             |   93 +++++++++++++++++++++++++++++++++++++++
>>>>>  include/hw/ppc/spapr.h          |   17 +++++++
>>>>>  pc-bios/spapr-rtas/spapr-rtas.S |   38 ++++++++++++++++
>>>>>  4 files changed, 163 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
>>>>> index 8f16160..eceb5e5 100644
>>>>> --- a/hw/ppc/spapr_hcall.c
>>>>> +++ b/hw/ppc/spapr_hcall.c
>>>>> @@ -97,6 +97,9 @@ struct rtas_mc_log {
>>>>>      struct rtas_error_log err_log;
>>>>>  };
>>>>>  
>>>>> +/* Whether machine check handling is in progress by any CPU */
>>>>> +bool mc_in_progress;
>>>>> +
>>>>>  static void do_spr_sync(void *arg)
>>>>>  {
>>>>>      struct SPRSyncState *s = arg;
>>>>> @@ -678,6 +681,19 @@ static target_ulong h_report_mc_err(PowerPCCPU *cpu, sPAPREnvironment *spapr,
>>>>>      cpu_synchronize_state(CPU(ppc_env_get_cpu(env)));
>>>>>  
>>>>>      /*
>>>>> +     * Only one VCPU can process machine check NMI at a time. Hence
>>>>> +     * set the lock mc_in_progress. Once the VCPU finishes processing
>>>>> +     * NMI, it executes ibm,nmi-interlock and mc_in_progress is unset
>>>>> +     * in ibm,nmi-interlock handler. Meanwhile if other VCPUs encounter
>>>>> +     * NMI we return 0 asking the VCPU to retry h_report_mc_err
>>>>> +     */
>>>>> +    if (mc_in_progress == 1) {
>>>>
>>>> Please don't depend on bools being numbers. Use true / false. For if()s,
>>>> just don't use == at all - it makes it more readable.
>>>
>>> ok
>>>
>>>>
>>>>> +        return 0;
>>>>> +    }
>>>>> +
>>>>> +    mc_in_progress = 1;
>>>>> +
>>>>> +    /*
>>>>>       * 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
>>>>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>>>>> index 2ec2a8e..71c7662 100644
>>>>> --- a/hw/ppc/spapr_rtas.c
>>>>> +++ b/hw/ppc/spapr_rtas.c
>>>>> @@ -36,6 +36,9 @@
>>>>>  
>>>>>  #include <libfdt.h>
>>>>>  
>>>>> +#define BRANCH_INST_MASK  0xFC000000
>>>>> +extern bool mc_in_progress;
>>>>
>>>> Please put this into the spapr struct.
>>>
>>> ok
>>>
>>>>
>>>>> +
>>>>>  static void rtas_display_character(PowerPCCPU *cpu, sPAPREnvironment *spapr,
>>>>>                                     uint32_t token, uint32_t nargs,
>>>>>                                     target_ulong args,
>>>>> @@ -290,6 +293,90 @@ static void rtas_ibm_os_term(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 ori_inst = 0x60630000;
>>>>> +    uint32_t branch_inst = 0x48000002;
>>>>> +    target_ulong guest_machine_check_addr;
>>>>> +    uint32_t trampoline[TRAMPOLINE_INSTS];
>>>>> +    int total_inst = sizeof(trampoline) / sizeof(uint32_t);
>>>>
>>>> ARRAY_SIZE(trampoline), though I don't quite understand why you need a
>>>> variable that contains the same value as a constant (TRAMPOLINE_INSTS).
>>>>
>>>> But since you're moving all of those bits into variable fields on the
>>>> rtas blob itself as we discussed in the last version, I guess this code
>>>> will go away anyways ;).
>>>
>>> I think we still need this. We need to patch the KVMPPC_H_REPORT_MC_ERR
>>> number and branch address in the trampoline and also, depending on
>>> whether the guest running in LE/BE we may need to flip the bits in the
>>> trampoline before copying it to 0x200 machine check vector.
>>>
>>> As rtas-blob is part of the guest memory I do not want to patch these in
>>> rtas-blob, hence I copy the trampoline from the rtas-blob to an array,
>>> modify accordingly and then move it to 0x200 machine check vector.
>>
>> Yes, you will still need the array. But the array should be dynamically
>> sized based on spapr->rtas_info->fwnmi_size which you extract from the

spapr->rtas_info.fwnmi_size of course ;). No need for yet another
allocation to keep track of.

>> blob on load.
>>
>> That way you wouldn't need the "total_inst" variable anymore ;).
> 
> Yes, I will fix it that way.
> 
>>
>>>
>>>>
>>>>> +    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
>>>>> +
>>>>> +    /* Store the system reset and machine check address */
>>>>> +    guest_machine_check_addr = rtas_ld(args, 1);
>>>>
>>>> Load or Store? I don't find the comment particularly useful either ;).
>>>
>>> will reword it or may delete it.
>>>
>>>>
>>>>> +
>>>>> +    /*
>>>>> +     * Read the trampoline instructions from RTAS Blob and patch
>>>>> +     * the KVMPPC_H_REPORT_MC_ERR hcall number and the guest
>>>>> +     * machine check address before copying to 0x200 vector
>>>>> +     */
>>>>> +    cpu_physical_memory_read(spapr->rtas_addr + RTAS_TRAMPOLINE_OFFSET,
>>>>> +                             trampoline, sizeof(trampoline));
>>>>> +
>>>>> +    /* Safety Check */
>>>>
>>>> Same for this comment.
>>>
>>> we have only 0x100 bytes that can be copied at 0x200. If the trampoline
>>> size exceeds then the next interrupt vector code is overwritten. Hence a
>>> safety check during compile time to make sure trampoline is within 0x100
>>> bytes.
>>
>> I think the check is fine, the comment is just redundant with
>> QEMU_BUILD_BUG_ON. Either be more verbose in the comment or remove it
> 
> I will add above lines as comment.

Awesome. You can also move the check to rtas load time, since the size
will be defined by the blob with your next version ;).


Alex