diff mbox series

[2/2] target/ppc/kvm: Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support

Message ID 20220214111749.1542196-2-npiggin@gmail.com
State New
Headers show
Series [1/2] spapr: Add SPAPR_CAP_AIL_MODE_3 for AIL mode 3 support for H_SET_MODE hcall | expand

Commit Message

Nicholas Piggin Feb. 14, 2022, 11:17 a.m. UTC 
Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support for KVM
guests. Keep the fallback heuristic for KVM hosts that pre-date this
CAP.

This is only proposed the KVM CAP has not yet been allocated. I will
ask to merge the new KVM cap when there are no objections on the QEMU
side.

not-yet-Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 hw/ppc/spapr_caps.c       |  2 +-
 linux-headers/linux/kvm.h |  1 +
 target/ppc/kvm.c          | 18 +++++++++++++++++-
 target/ppc/kvm_ppc.h      |  4 ++--
 4 files changed, 21 insertions(+), 4 deletions(-)

Comments

Fabiano Rosas Feb. 14, 2022, 1:13 p.m. UTC | #1 
Nicholas Piggin <npiggin@gmail.com> writes:

> Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support for KVM
> guests. Keep the fallback heuristic for KVM hosts that pre-date this
> CAP.
>
> This is only proposed the KVM CAP has not yet been allocated. I will
> ask to merge the new KVM cap when there are no objections on the QEMU
> side.
>
> not-yet-Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  hw/ppc/spapr_caps.c       |  2 +-
>  linux-headers/linux/kvm.h |  1 +
>  target/ppc/kvm.c          | 18 +++++++++++++++++-
>  target/ppc/kvm_ppc.h      |  4 ++--
>  4 files changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index 5fd4a53c33..5cc80776d0 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -619,7 +619,7 @@ static void cap_ail_mode_3_apply(SpaprMachineState *spapr,
>      ERRP_GUARD();
>  
>      if (kvm_enabled()) {
> -        if (!kvmppc_supports_ail_3()) {
> +        if (!kvmppc_has_cap_ail_3()) {
>              error_setg(errp, "KVM implementation does not support cap-ail-mode-3");
>              error_append_hint(errp, "Try appending -machine cap-ail-mode-3=off\n");
>              return;
> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
> index 02c5e7b7bb..d91f578200 100644
> --- a/linux-headers/linux/kvm.h
> +++ b/linux-headers/linux/kvm.h
> @@ -1130,6 +1130,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_BINARY_STATS_FD 203
>  #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>  #define KVM_CAP_ARM_MTE 205
> +#define KVM_CAP_PPC_AIL_MODE_3 210
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 128bc530d4..d0d0bdaac4 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -90,6 +90,7 @@ static int cap_ppc_nested_kvm_hv;
>  static int cap_large_decr;
>  static int cap_fwnmi;
>  static int cap_rpt_invalidate;
> +static int cap_ail_mode_3;
>  
>  static uint32_t debug_inst_opcode;
>  
> @@ -154,6 +155,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>      }
>  
>      cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
> +    cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
>      kvm_ppc_register_host_cpu_type();
>  
>      return 0;
> @@ -2563,10 +2565,24 @@ int kvmppc_has_cap_rpt_invalidate(void)
>      return cap_rpt_invalidate;
>  }
>  
> -int kvmppc_supports_ail_3(void)
> +int kvmppc_has_cap_ail_3(void)
>  {
>      PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
>  
> +    if (cap_ail_mode_3) {
> +        return 1;
> +    }
> +
> +    if (kvm_ioctl(kvm_state, KVM_CHECK_EXTENSION, KVM_CAP_PPC_AIL_MODE_3) == 0) {
> +        return 0;
> +    }

This is not needed here it seems.

> +
> +    /*
> +     * For KVM hosts that pre-date this cap, special-case the test because
> +     * the performance cost for disabling the feature unconditionally is
> +     * prohibitive.
> +     */
> +
>      /*
>       * KVM PR only supports AIL-0
>       */
> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> index d9d1c54955..efafa67b83 100644
> --- a/target/ppc/kvm_ppc.h
> +++ b/target/ppc/kvm_ppc.h
> @@ -73,7 +73,7 @@ int kvmppc_set_cap_nested_kvm_hv(int enable);
>  int kvmppc_get_cap_large_decr(void);
>  int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable);
>  int kvmppc_has_cap_rpt_invalidate(void);
> -int kvmppc_supports_ail_3(void);
> +int kvmppc_has_cap_ail_3(void);
>  int kvmppc_enable_hwrng(void);
>  int kvmppc_put_books_sregs(PowerPCCPU *cpu);
>  PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void);
> @@ -394,7 +394,7 @@ static inline int kvmppc_has_cap_rpt_invalidate(void)
>      return false;
>  }
>  
> -static inline int kvmppc_supports_ail_3(void)
> +static inline int kvmppc_has_cap_ail_3(void)
>  {
>      return false;
>  }
Nicholas Piggin Feb. 14, 2022, 10:54 p.m. UTC | #2 
Excerpts from Fabiano Rosas's message of February 14, 2022 11:13 pm:
> Nicholas Piggin <npiggin@gmail.com> writes:
> 
>> Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support for KVM
>> guests. Keep the fallback heuristic for KVM hosts that pre-date this
>> CAP.
>>
>> This is only proposed the KVM CAP has not yet been allocated. I will
>> ask to merge the new KVM cap when there are no objections on the QEMU
>> side.
>>
>> not-yet-Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>>  hw/ppc/spapr_caps.c       |  2 +-
>>  linux-headers/linux/kvm.h |  1 +
>>  target/ppc/kvm.c          | 18 +++++++++++++++++-
>>  target/ppc/kvm_ppc.h      |  4 ++--
>>  4 files changed, 21 insertions(+), 4 deletions(-)
>>
>> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
>> index 5fd4a53c33..5cc80776d0 100644
>> --- a/hw/ppc/spapr_caps.c
>> +++ b/hw/ppc/spapr_caps.c
>> @@ -619,7 +619,7 @@ static void cap_ail_mode_3_apply(SpaprMachineState *spapr,
>>      ERRP_GUARD();
>>  
>>      if (kvm_enabled()) {
>> -        if (!kvmppc_supports_ail_3()) {
>> +        if (!kvmppc_has_cap_ail_3()) {
>>              error_setg(errp, "KVM implementation does not support cap-ail-mode-3");
>>              error_append_hint(errp, "Try appending -machine cap-ail-mode-3=off\n");
>>              return;
>> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
>> index 02c5e7b7bb..d91f578200 100644
>> --- a/linux-headers/linux/kvm.h
>> +++ b/linux-headers/linux/kvm.h
>> @@ -1130,6 +1130,7 @@ struct kvm_ppc_resize_hpt {
>>  #define KVM_CAP_BINARY_STATS_FD 203
>>  #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>>  #define KVM_CAP_ARM_MTE 205
>> +#define KVM_CAP_PPC_AIL_MODE_3 210
>>  
>>  #ifdef KVM_CAP_IRQ_ROUTING
>>  
>> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
>> index 128bc530d4..d0d0bdaac4 100644
>> --- a/target/ppc/kvm.c
>> +++ b/target/ppc/kvm.c
>> @@ -90,6 +90,7 @@ static int cap_ppc_nested_kvm_hv;
>>  static int cap_large_decr;
>>  static int cap_fwnmi;
>>  static int cap_rpt_invalidate;
>> +static int cap_ail_mode_3;
>>  
>>  static uint32_t debug_inst_opcode;
>>  
>> @@ -154,6 +155,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>>      }
>>  
>>      cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
>> +    cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
>>      kvm_ppc_register_host_cpu_type();
>>  
>>      return 0;
>> @@ -2563,10 +2565,24 @@ int kvmppc_has_cap_rpt_invalidate(void)
>>      return cap_rpt_invalidate;
>>  }
>>  
>> -int kvmppc_supports_ail_3(void)
>> +int kvmppc_has_cap_ail_3(void)
>>  {
>>      PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
>>  
>> +    if (cap_ail_mode_3) {
>> +        return 1;
>> +    }
>> +
>> +    if (kvm_ioctl(kvm_state, KVM_CHECK_EXTENSION, KVM_CAP_PPC_AIL_MODE_3) == 0) {
>> +        return 0;
>> +    }
> 
> This is not needed here it seems.

This is to test whether the capability is recognised by the HV. 
kvm_vm_check_extension() treats ioctl error as 0 capability but we want 
to do this extra heuristic.

I'm not sure if there's a better standard way to do this.

Thanks,
Nick
Fabiano Rosas Feb. 15, 2022, 12:21 p.m. UTC | #3 
Nicholas Piggin <npiggin@gmail.com> writes:

> Excerpts from Fabiano Rosas's message of February 14, 2022 11:13 pm:
>> Nicholas Piggin <npiggin@gmail.com> writes:
>> 
>>> Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support for KVM
>>> guests. Keep the fallback heuristic for KVM hosts that pre-date this
>>> CAP.
>>>
>>> This is only proposed the KVM CAP has not yet been allocated. I will
>>> ask to merge the new KVM cap when there are no objections on the QEMU
>>> side.
>>>
>>> not-yet-Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>>> ---
>>>  hw/ppc/spapr_caps.c       |  2 +-
>>>  linux-headers/linux/kvm.h |  1 +
>>>  target/ppc/kvm.c          | 18 +++++++++++++++++-
>>>  target/ppc/kvm_ppc.h      |  4 ++--
>>>  4 files changed, 21 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
>>> index 5fd4a53c33..5cc80776d0 100644
>>> --- a/hw/ppc/spapr_caps.c
>>> +++ b/hw/ppc/spapr_caps.c
>>> @@ -619,7 +619,7 @@ static void cap_ail_mode_3_apply(SpaprMachineState *spapr,
>>>      ERRP_GUARD();
>>>  
>>>      if (kvm_enabled()) {
>>> -        if (!kvmppc_supports_ail_3()) {
>>> +        if (!kvmppc_has_cap_ail_3()) {
>>>              error_setg(errp, "KVM implementation does not support cap-ail-mode-3");
>>>              error_append_hint(errp, "Try appending -machine cap-ail-mode-3=off\n");
>>>              return;
>>> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
>>> index 02c5e7b7bb..d91f578200 100644
>>> --- a/linux-headers/linux/kvm.h
>>> +++ b/linux-headers/linux/kvm.h
>>> @@ -1130,6 +1130,7 @@ struct kvm_ppc_resize_hpt {
>>>  #define KVM_CAP_BINARY_STATS_FD 203
>>>  #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>>>  #define KVM_CAP_ARM_MTE 205
>>> +#define KVM_CAP_PPC_AIL_MODE_3 210
>>>  
>>>  #ifdef KVM_CAP_IRQ_ROUTING
>>>  
>>> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
>>> index 128bc530d4..d0d0bdaac4 100644
>>> --- a/target/ppc/kvm.c
>>> +++ b/target/ppc/kvm.c
>>> @@ -90,6 +90,7 @@ static int cap_ppc_nested_kvm_hv;
>>>  static int cap_large_decr;
>>>  static int cap_fwnmi;
>>>  static int cap_rpt_invalidate;
>>> +static int cap_ail_mode_3;
>>>  
>>>  static uint32_t debug_inst_opcode;
>>>  
>>> @@ -154,6 +155,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>>>      }
>>>  
>>>      cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
>>> +    cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
>>>      kvm_ppc_register_host_cpu_type();
>>>  
>>>      return 0;
>>> @@ -2563,10 +2565,24 @@ int kvmppc_has_cap_rpt_invalidate(void)
>>>      return cap_rpt_invalidate;
>>>  }
>>>  
>>> -int kvmppc_supports_ail_3(void)
>>> +int kvmppc_has_cap_ail_3(void)
>>>  {
>>>      PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
>>>  
>>> +    if (cap_ail_mode_3) {
>>> +        return 1;
>>> +    }
>>> +
>>> +    if (kvm_ioctl(kvm_state, KVM_CHECK_EXTENSION, KVM_CAP_PPC_AIL_MODE_3) == 0) {
>>> +        return 0;
>>> +    }
>> 
>> This is not needed here it seems.
>
> This is to test whether the capability is recognised by the HV. 
> kvm_vm_check_extension() treats ioctl error as 0 capability but we want 
> to do this extra heuristic.

Do you intend to make the KVM capability return < 0 in case AIL_3 is not
supported? AFAICS the unknown capability won't result in an ioctl error
as kvm_vm_ioctl_check_extension always returns >= 0.

>
> I'm not sure if there's a better standard way to do this.
>
> Thanks,
> Nick
Nicholas Piggin Feb. 16, 2022, 1:46 a.m. UTC | #4 
Excerpts from Fabiano Rosas's message of February 15, 2022 10:21 pm:
> Nicholas Piggin <npiggin@gmail.com> writes:
> 
>> Excerpts from Fabiano Rosas's message of February 14, 2022 11:13 pm:
>>> Nicholas Piggin <npiggin@gmail.com> writes:
>>> 
>>>> Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support for KVM
>>>> guests. Keep the fallback heuristic for KVM hosts that pre-date this
>>>> CAP.
>>>>
>>>> This is only proposed the KVM CAP has not yet been allocated. I will
>>>> ask to merge the new KVM cap when there are no objections on the QEMU
>>>> side.
>>>>
>>>> not-yet-Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>>>> ---
>>>>  hw/ppc/spapr_caps.c       |  2 +-
>>>>  linux-headers/linux/kvm.h |  1 +
>>>>  target/ppc/kvm.c          | 18 +++++++++++++++++-
>>>>  target/ppc/kvm_ppc.h      |  4 ++--
>>>>  4 files changed, 21 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
>>>> index 5fd4a53c33..5cc80776d0 100644
>>>> --- a/hw/ppc/spapr_caps.c
>>>> +++ b/hw/ppc/spapr_caps.c
>>>> @@ -619,7 +619,7 @@ static void cap_ail_mode_3_apply(SpaprMachineState *spapr,
>>>>      ERRP_GUARD();
>>>>  
>>>>      if (kvm_enabled()) {
>>>> -        if (!kvmppc_supports_ail_3()) {
>>>> +        if (!kvmppc_has_cap_ail_3()) {
>>>>              error_setg(errp, "KVM implementation does not support cap-ail-mode-3");
>>>>              error_append_hint(errp, "Try appending -machine cap-ail-mode-3=off\n");
>>>>              return;
>>>> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
>>>> index 02c5e7b7bb..d91f578200 100644
>>>> --- a/linux-headers/linux/kvm.h
>>>> +++ b/linux-headers/linux/kvm.h
>>>> @@ -1130,6 +1130,7 @@ struct kvm_ppc_resize_hpt {
>>>>  #define KVM_CAP_BINARY_STATS_FD 203
>>>>  #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>>>>  #define KVM_CAP_ARM_MTE 205
>>>> +#define KVM_CAP_PPC_AIL_MODE_3 210
>>>>  
>>>>  #ifdef KVM_CAP_IRQ_ROUTING
>>>>  
>>>> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
>>>> index 128bc530d4..d0d0bdaac4 100644
>>>> --- a/target/ppc/kvm.c
>>>> +++ b/target/ppc/kvm.c
>>>> @@ -90,6 +90,7 @@ static int cap_ppc_nested_kvm_hv;
>>>>  static int cap_large_decr;
>>>>  static int cap_fwnmi;
>>>>  static int cap_rpt_invalidate;
>>>> +static int cap_ail_mode_3;
>>>>  
>>>>  static uint32_t debug_inst_opcode;
>>>>  
>>>> @@ -154,6 +155,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>>>>      }
>>>>  
>>>>      cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
>>>> +    cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
>>>>      kvm_ppc_register_host_cpu_type();
>>>>  
>>>>      return 0;
>>>> @@ -2563,10 +2565,24 @@ int kvmppc_has_cap_rpt_invalidate(void)
>>>>      return cap_rpt_invalidate;
>>>>  }
>>>>  
>>>> -int kvmppc_supports_ail_3(void)
>>>> +int kvmppc_has_cap_ail_3(void)
>>>>  {
>>>>      PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
>>>>  
>>>> +    if (cap_ail_mode_3) {
>>>> +        return 1;
>>>> +    }
>>>> +
>>>> +    if (kvm_ioctl(kvm_state, KVM_CHECK_EXTENSION, KVM_CAP_PPC_AIL_MODE_3) == 0) {
>>>> +        return 0;
>>>> +    }
>>> 
>>> This is not needed here it seems.
>>
>> This is to test whether the capability is recognised by the HV. 
>> kvm_vm_check_extension() treats ioctl error as 0 capability but we want 
>> to do this extra heuristic.
> 
> Do you intend to make the KVM capability return < 0 in case AIL_3 is not
> supported?

No it should return 0 in that case.

> AFAICS the unknown capability won't result in an ioctl error
> as kvm_vm_ioctl_check_extension always returns >= 0.

Oh. There is no way to tell that a host does not recognise a cap? :(

Great for the purity test, unknown cap == unsupported. For a practical 
point of view to catch such bugs and oversights there should have been
some way to handle it.

I'm not sure what to do then. Try some even worse hack and leave that
in for a couple of years to give upstream KVM a chance to trickle down.

Thanks,
Nick
David Gibson Feb. 16, 2022, 4:58 a.m. UTC | #5 
>On Wed, Feb 16, 2022 at 11:46:58AM +1000, Nicholas Piggin wrote:
> Excerpts from Fabiano Rosas's message of February 15, 2022 10:21 pm:
> > Nicholas Piggin <npiggin@gmail.com> writes:
> > 
> >> Excerpts from Fabiano Rosas's message of February 14, 2022 11:13 pm:
> >>> Nicholas Piggin <npiggin@gmail.com> writes:
> >>> 
> >>>> Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support for KVM
> >>>> guests. Keep the fallback heuristic for KVM hosts that pre-date this
> >>>> CAP.
> >>>>
> >>>> This is only proposed the KVM CAP has not yet been allocated. I will
> >>>> ask to merge the new KVM cap when there are no objections on the QEMU
> >>>> side.
> >>>>
> >>>> not-yet-Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> >>>> ---
> >>>>  hw/ppc/spapr_caps.c       |  2 +-
> >>>>  linux-headers/linux/kvm.h |  1 +
> >>>>  target/ppc/kvm.c          | 18 +++++++++++++++++-
> >>>>  target/ppc/kvm_ppc.h      |  4 ++--
> >>>>  4 files changed, 21 insertions(+), 4 deletions(-)
> >>>>
> >>>> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> >>>> index 5fd4a53c33..5cc80776d0 100644
> >>>> --- a/hw/ppc/spapr_caps.c
> >>>> +++ b/hw/ppc/spapr_caps.c
> >>>> @@ -619,7 +619,7 @@ static void cap_ail_mode_3_apply(SpaprMachineState *spapr,
> >>>>      ERRP_GUARD();
> >>>>  
> >>>>      if (kvm_enabled()) {
> >>>> -        if (!kvmppc_supports_ail_3()) {
> >>>> +        if (!kvmppc_has_cap_ail_3()) {
> >>>>              error_setg(errp, "KVM implementation does not support cap-ail-mode-3");
> >>>>              error_append_hint(errp, "Try appending -machine cap-ail-mode-3=off\n");
> >>>>              return;
> >>>> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
> >>>> index 02c5e7b7bb..d91f578200 100644
> >>>> --- a/linux-headers/linux/kvm.h
> >>>> +++ b/linux-headers/linux/kvm.h
> >>>> @@ -1130,6 +1130,7 @@ struct kvm_ppc_resize_hpt {
> >>>>  #define KVM_CAP_BINARY_STATS_FD 203
> >>>>  #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
> >>>>  #define KVM_CAP_ARM_MTE 205
> >>>> +#define KVM_CAP_PPC_AIL_MODE_3 210
> >>>>  
> >>>>  #ifdef KVM_CAP_IRQ_ROUTING
> >>>>  
> >>>> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> >>>> index 128bc530d4..d0d0bdaac4 100644
> >>>> --- a/target/ppc/kvm.c
> >>>> +++ b/target/ppc/kvm.c
> >>>> @@ -90,6 +90,7 @@ static int cap_ppc_nested_kvm_hv;
> >>>>  static int cap_large_decr;
> >>>>  static int cap_fwnmi;
> >>>>  static int cap_rpt_invalidate;
> >>>> +static int cap_ail_mode_3;
> >>>>  
> >>>>  static uint32_t debug_inst_opcode;
> >>>>  
> >>>> @@ -154,6 +155,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> >>>>      }
> >>>>  
> >>>>      cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
> >>>> +    cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
> >>>>      kvm_ppc_register_host_cpu_type();
> >>>>  
> >>>>      return 0;
> >>>> @@ -2563,10 +2565,24 @@ int kvmppc_has_cap_rpt_invalidate(void)
> >>>>      return cap_rpt_invalidate;
> >>>>  }
> >>>>  
> >>>> -int kvmppc_supports_ail_3(void)
> >>>> +int kvmppc_has_cap_ail_3(void)
> >>>>  {
> >>>>      PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
> >>>>  
> >>>> +    if (cap_ail_mode_3) {
> >>>> +        return 1;
> >>>> +    }
> >>>> +
> >>>> +    if (kvm_ioctl(kvm_state, KVM_CHECK_EXTENSION, KVM_CAP_PPC_AIL_MODE_3) == 0) {
> >>>> +        return 0;
> >>>> +    }
> >>> 
> >>> This is not needed here it seems.
> >>
> >> This is to test whether the capability is recognised by the HV. 
> >> kvm_vm_check_extension() treats ioctl error as 0 capability but we want 
> >> to do this extra heuristic.
> > 
> > Do you intend to make the KVM capability return < 0 in case AIL_3 is not
> > supported?
> 
> No it should return 0 in that case.
> 
> > AFAICS the unknown capability won't result in an ioctl error
> > as kvm_vm_ioctl_check_extension always returns >= 0.
> 
> Oh. There is no way to tell that a host does not recognise a cap? :(

Not short of giving it all non-zero values when you create the new cap.

> Great for the purity test, unknown cap == unsupported. For a practical 
> point of view to catch such bugs and oversights there should have been
> some way to handle it.

Yeah :(.

> I'm not sure what to do then. Try some even worse hack and leave that
> in for a couple of years to give upstream KVM a chance to trickle down.
> 
> Thanks,
> Nick
>
diff mbox series

Patch

diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 5fd4a53c33..5cc80776d0 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -619,7 +619,7 @@  static void cap_ail_mode_3_apply(SpaprMachineState *spapr,
     ERRP_GUARD();
 
     if (kvm_enabled()) {
-        if (!kvmppc_supports_ail_3()) {
+        if (!kvmppc_has_cap_ail_3()) {
             error_setg(errp, "KVM implementation does not support cap-ail-mode-3");
             error_append_hint(errp, "Try appending -machine cap-ail-mode-3=off\n");
             return;
diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
index 02c5e7b7bb..d91f578200 100644
--- a/linux-headers/linux/kvm.h
+++ b/linux-headers/linux/kvm.h
@@ -1130,6 +1130,7 @@  struct kvm_ppc_resize_hpt {
 #define KVM_CAP_BINARY_STATS_FD 203
 #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
 #define KVM_CAP_ARM_MTE 205
+#define KVM_CAP_PPC_AIL_MODE_3 210
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 128bc530d4..d0d0bdaac4 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -90,6 +90,7 @@  static int cap_ppc_nested_kvm_hv;
 static int cap_large_decr;
 static int cap_fwnmi;
 static int cap_rpt_invalidate;
+static int cap_ail_mode_3;
 
 static uint32_t debug_inst_opcode;
 
@@ -154,6 +155,7 @@  int kvm_arch_init(MachineState *ms, KVMState *s)
     }
 
     cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
+    cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
     kvm_ppc_register_host_cpu_type();
 
     return 0;
@@ -2563,10 +2565,24 @@  int kvmppc_has_cap_rpt_invalidate(void)
     return cap_rpt_invalidate;
 }
 
-int kvmppc_supports_ail_3(void)
+int kvmppc_has_cap_ail_3(void)
 {
     PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
 
+    if (cap_ail_mode_3) {
+        return 1;
+    }
+
+    if (kvm_ioctl(kvm_state, KVM_CHECK_EXTENSION, KVM_CAP_PPC_AIL_MODE_3) == 0) {
+        return 0;
+    }
+
+    /*
+     * For KVM hosts that pre-date this cap, special-case the test because
+     * the performance cost for disabling the feature unconditionally is
+     * prohibitive.
+     */
+
     /*
      * KVM PR only supports AIL-0
      */
diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
index d9d1c54955..efafa67b83 100644
--- a/target/ppc/kvm_ppc.h
+++ b/target/ppc/kvm_ppc.h
@@ -73,7 +73,7 @@  int kvmppc_set_cap_nested_kvm_hv(int enable);
 int kvmppc_get_cap_large_decr(void);
 int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable);
 int kvmppc_has_cap_rpt_invalidate(void);
-int kvmppc_supports_ail_3(void);
+int kvmppc_has_cap_ail_3(void);
 int kvmppc_enable_hwrng(void);
 int kvmppc_put_books_sregs(PowerPCCPU *cpu);
 PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void);
@@ -394,7 +394,7 @@  static inline int kvmppc_has_cap_rpt_invalidate(void)
     return false;
 }
 
-static inline int kvmppc_supports_ail_3(void)
+static inline int kvmppc_has_cap_ail_3(void)
 {
     return false;
 }