Re: [Qemu-devel] [PATCH v7 3/6] target/ppc: Handle NMI guest exit

[Aravinda Prasad]

On Monday 25 March 2019 11:52 AM, David Gibson wrote:
> On Fri, Mar 22, 2019 at 12:03:58PM +0530, Aravinda Prasad wrote:
>> Memory error such as bit flips that cannot be corrected
>> by hardware are passed on to the kernel for handling.
>> If the memory address in error belongs to guest then
>> the guest kernel is responsible for taking suitable action.
>> Patch [1] enhances KVM to exit guest with exit reason
>> set to KVM_EXIT_NMI in such cases. This patch handles
>> KVM_EXIT_NMI exit.
>>
>> [1] https://www.spinics.net/lists/kvm-ppc/msg12637.html
>>     (e20bbd3d and related commits)
>>
>> Signed-off-by: Aravinda Prasad <address@hidden>
>> ---
>>  hw/ppc/spapr_events.c  |   22 ++++++++++++++++++++++
>>  include/hw/ppc/spapr.h |    1 +
>>  target/ppc/kvm.c       |   16 ++++++++++++++++
>>  target/ppc/kvm_ppc.h   |    2 ++
>>  4 files changed, 41 insertions(+)
>>
>> diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
>> index ae0f093..e7a24ad 100644
>> --- a/hw/ppc/spapr_events.c
>> +++ b/hw/ppc/spapr_events.c
>> @@ -620,6 +620,28 @@ void 
>> spapr_hotplug_req_remove_by_count_indexed(SpaprDrcType drc_type,
>>                              RTAS_LOG_V6_HP_ACTION_REMOVE, drc_type, 
>> &drc_id);
>>  }
>>  
>> +void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered)
>> +{
>> +    SpaprMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
>> +
>> +    while (spapr->mc_status != -1) {
>> +        /*
>> +         * Check whether the same CPU got machine check error
>> +         * while still handling the mc error (i.e., before
>> +         * that CPU called "ibm,nmi-interlock"
>> +         */
>> +        if (spapr->mc_status == cpu->vcpu_id) {
>> +            qemu_system_guest_panicked(NULL);
>> +        }
>> +        qemu_cond_wait_iothread(&spapr->mc_delivery_cond);
>> +        /* If the system is reset meanwhile, then just return */
>> +        if (spapr->mc_reset) {
> 
> I don't really see what this accomplishes.  IIUC mc_reset is true from
> reset time until nmi-register is called.  Which means you could just
> check for guest_mnachine_check_addre being unset - in which case don't
> you need to fallback to the old machine check behaviour anyway?

We can check for guest_machine_check_addr being unset instead of mc_reset.

Do we need any kind of memory barriers to ensure that this thread reads
the updated guest_machine_check_addr/mc_reset?

We don't have to fallback to the old machine check behavior, because
guest_machine_check_addr is unset only during system reset.

> 
>> +            return;
>> +        }
>> +    }
>> +    spapr->mc_status = cpu->vcpu_id;
>> +}
>> +
>>  static void check_exception(PowerPCCPU *cpu, SpaprMachineState *spapr,
>>                              uint32_t token, uint32_t nargs,
>>                              target_ulong args,
>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>> index ee5589d..b0d8c18 100644
>> --- a/include/hw/ppc/spapr.h
>> +++ b/include/hw/ppc/spapr.h
>> @@ -792,6 +792,7 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr, int 
>> shift,
>>                            Error **errp);
>>  void spapr_clear_pending_events(SpaprMachineState *spapr);
>>  int spapr_max_server_number(SpaprMachineState *spapr);
>> +void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered);
>>  
>>  /* DRC callbacks. */
>>  void spapr_core_release(DeviceState *dev);
>> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
>> index 2427c8e..a593448 100644
>> --- a/target/ppc/kvm.c
>> +++ b/target/ppc/kvm.c
>> @@ -1738,6 +1738,11 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run 
>> *run)
>>          ret = 0;
>>          break;
>>  
>> +    case KVM_EXIT_NMI:
>> +        DPRINTF("handle NMI exception\n");
> 
> tracepoints are generally preferred to new DPRINTFs.

sure.

> 
>> +        ret = kvm_handle_nmi(cpu, run);
>> +        break;
>> +
>>      default:
>>          fprintf(stderr, "KVM: unknown exit reason %d\n", run->exit_reason);
>>          ret = -1;
>> @@ -2803,6 +2808,17 @@ int kvm_arch_msi_data_to_gsi(uint32_t data)
>>      return data & 0xffff;
>>  }
>>  
>> +int kvm_handle_nmi(PowerPCCPU *cpu, struct kvm_run *run)
>> +{
>> +    bool recovered = run->flags & KVM_RUN_PPC_NMI_DISP_FULLY_RECOV;
>> +
>> +    cpu_synchronize_state(CPU(cpu));
>> +
>> +    spapr_mce_req_event(cpu, recovered);
>> +
>> +    return 0;
>> +}
>> +
>>  int kvmppc_enable_hwrng(void)
>>  {
>>      if (!kvm_enabled() || !kvm_check_extension(kvm_state, 
>> KVM_CAP_PPC_HWRNG)) {
>> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
>> index 2c2ea30..df5e85f 100644
>> --- a/target/ppc/kvm_ppc.h
>> +++ b/target/ppc/kvm_ppc.h
>> @@ -80,6 +80,8 @@ bool kvmppc_hpt_needs_host_contiguous_pages(void);
>>  void kvm_check_mmu(PowerPCCPU *cpu, Error **errp);
>>  void kvmppc_set_reg_ppc_online(PowerPCCPU *cpu, unsigned int online);
>>  
>> +int kvm_handle_nmi(PowerPCCPU *cpu, struct kvm_run *run);
>> +
>>  #else
>>  
>>  static inline uint32_t kvmppc_get_tbfreq(void)
>>
> 

-- 
Regards,
Aravinda