Re: [PATCH v5 14/14] spapr: nested: Introduce cap-nested-papr for Nested PAPR API

[Harsh Prateek Bora <harshpb@linux.ibm.com>]

Hi Nick,

On 3/12/24 17:41, Harsh Prateek Bora wrote:
> Hi Nick,
> 
> On 3/12/24 17:21, Nicholas Piggin wrote:
>> On Fri Mar 8, 2024 at 9:19 PM AEST, Harsh Prateek Bora wrote:
>>> Introduce a SPAPR capability cap-nested-papr which enables nested PAPR
>>> API for nested guests. This new API is to enable support for KVM on 
>>> PowerVM
>>> and the support in Linux kernel has already merged upstream.
>>>
>>> Signed-off-by: Michael Neuling <mikey@neuling.org>
>>> Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
>>> ---
>>>   include/hw/ppc/spapr.h |  6 +++-
>>>   hw/ppc/spapr.c         |  2 ++
>>>   hw/ppc/spapr_caps.c    | 62 ++++++++++++++++++++++++++++++++++++++++++
>>>   hw/ppc/spapr_nested.c  |  8 ++++--
>>>   4 files changed, 74 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>>> index 6223873641..4aaf23d28f 100644
>>> --- a/include/hw/ppc/spapr.h
>>> +++ b/include/hw/ppc/spapr.h
>>> @@ -81,8 +81,10 @@ typedef enum {
>>>   #define SPAPR_CAP_RPT_INVALIDATE        0x0B
>>>   /* Support for AIL modes */
>>>   #define SPAPR_CAP_AIL_MODE_3            0x0C
>>> +/* Nested PAPR */
>>> +#define SPAPR_CAP_NESTED_PAPR           0x0D
>>>   /* Num Caps */
>>> -#define SPAPR_CAP_NUM                   (SPAPR_CAP_AIL_MODE_3 + 1)
>>> +#define SPAPR_CAP_NUM                   (SPAPR_CAP_NESTED_PAPR + 1)
>>>   /*
>>>    * Capability Values
>>> @@ -592,6 +594,7 @@ struct SpaprMachineState {
>>>   #define H_GUEST_CREATE_VCPU      0x474
>>>   #define H_GUEST_GET_STATE        0x478
>>>   #define H_GUEST_SET_STATE        0x47C
>>> +#define H_GUEST_RUN_VCPU         0x480
>>>   #define H_GUEST_DELETE           0x488
>>>   #define MAX_HCALL_OPCODE         H_GUEST_DELETE
>>> @@ -996,6 +999,7 @@ extern const VMStateDescription 
>>> vmstate_spapr_cap_sbbc;
>>>   extern const VMStateDescription vmstate_spapr_cap_ibs;
>>>   extern const VMStateDescription vmstate_spapr_cap_hpt_maxpagesize;
>>>   extern const VMStateDescription vmstate_spapr_cap_nested_kvm_hv;
>>> +extern const VMStateDescription vmstate_spapr_cap_nested_papr;
>>>   extern const VMStateDescription vmstate_spapr_cap_large_decr;
>>>   extern const VMStateDescription vmstate_spapr_cap_ccf_assist;
>>>   extern const VMStateDescription vmstate_spapr_cap_fwnmi;
>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>>> index 54fc01e462..beb23fae8f 100644
>>> --- a/hw/ppc/spapr.c
>>> +++ b/hw/ppc/spapr.c
>>> @@ -2121,6 +2121,7 @@ static const VMStateDescription vmstate_spapr = {
>>>           &vmstate_spapr_cap_fwnmi,
>>>           &vmstate_spapr_fwnmi,
>>>           &vmstate_spapr_cap_rpt_invalidate,
>>> +        &vmstate_spapr_cap_nested_papr,
>>>           NULL
>>>       }
>>>   };
>>> @@ -4687,6 +4688,7 @@ static void 
>>> spapr_machine_class_init(ObjectClass *oc, void *data)
>>>       smc->default_caps.caps[SPAPR_CAP_IBS] = SPAPR_CAP_WORKAROUND;
>>>       smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] = 16; /* 
>>> 64kiB */
>>>       smc->default_caps.caps[SPAPR_CAP_NESTED_KVM_HV] = SPAPR_CAP_OFF;
>>> +    smc->default_caps.caps[SPAPR_CAP_NESTED_PAPR] = SPAPR_CAP_OFF;
>>>       smc->default_caps.caps[SPAPR_CAP_LARGE_DECREMENTER] = 
>>> SPAPR_CAP_ON;
>>>       smc->default_caps.caps[SPAPR_CAP_CCF_ASSIST] = SPAPR_CAP_ON;
>>>       smc->default_caps.caps[SPAPR_CAP_FWNMI] = SPAPR_CAP_ON;
>>> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
>>> index e889244e52..d6d5a6b8df 100644
>>> --- a/hw/ppc/spapr_caps.c
>>> +++ b/hw/ppc/spapr_caps.c
>>> @@ -487,6 +487,58 @@ static void 
>>> cap_nested_kvm_hv_apply(SpaprMachineState *spapr,
>>>               error_append_hint(errp, "Try appending -machine 
>>> cap-nested-hv=off "
>>>                                       "or use threads=1 with -smp\n");
>>>           }
>>> +        if (spapr_nested_api(spapr) &&
>>> +            spapr_nested_api(spapr) != NESTED_API_KVM_HV) {
>>> +            error_setg(errp, "Nested-HV APIs are mutually 
>>> exclusive/incompatible");
>>> +            error_append_hint(errp, "Please use either cap-nested-hv 
>>> or "
>>> +                                    "cap-nested-papr to proceed.\n");
>>> +            return;
>>> +        } else {
>>> +            spapr->nested.api = NESTED_API_KVM_HV;
>>> +        }
>>> +    }
>>> +}
>>> +
>>> +static void cap_nested_papr_apply(SpaprMachineState *spapr,
>>> +                                    uint8_t val, Error **errp)
>>> +{
>>> +    ERRP_GUARD();
>>> +    PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
>>> +    CPUPPCState *env = &cpu->env;
>>> +
>>> +    if (!val) {
>>> +        /* capability disabled by default */
>>> +        return;
>>> +    }
>>> +
>>> +    if (tcg_enabled()) {
>>> +        if (!(env->insns_flags2 & PPC2_ISA300)) {
>>> +            error_setg(errp, "Nested-PAPR only supported on POWER9 
>>> and later");
>>> +            error_append_hint(errp,
>>> +                              "Try appending -machine 
>>> cap-nested-papr=off\n");
>>> +            return;
>>> +        }
>>> +        if (spapr_nested_api(spapr) &&
>>> +            spapr_nested_api(spapr) != NESTED_API_PAPR) {
>>> +            error_setg(errp, "Nested-HV APIs are mutually 
>>> exclusive/incompatible");
>>> +            error_append_hint(errp, "Please use either cap-nested-hv 
>>> or "
>>> +                                    "cap-nested-papr to proceed.\n");
>>> +            return;
>>> +        } else {
>>> +            spapr->nested.api = NESTED_API_PAPR;
>>> +        }
>>> +
>>> +    } else if (kvm_enabled()) {
>>> +        /*
>>> +         * this gets executed in L1 qemu when L2 is launched,
>>> +         * needs kvm-hv support in L1 kernel.
>>> +         */
>>> +        if (!kvmppc_has_cap_nested_kvm_hv()) {
>>> +            error_setg(errp,
>>> +                       "KVM implementation does not support 
>>> Nested-HV");
>>> +        } else if (kvmppc_set_cap_nested_kvm_hv(val) < 0) {
>>> +            error_setg(errp, "Error enabling Nested-HV with KVM");
>>> +        }
>>
>> I'll just disable this on KVM for now. With that changed,
>>
>> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
>>
> 
> AFAIK, v2 api also expects this capability to be enabled on L1 kernel.
> I guess the reason is the L1 implementation has used the same capab and
> extended to be used with v2 api. So, this check is needed in L1 Qemu for
> now. We may revisit L1 implementation later to see if a change is
> appropriate.

Please ignore above response. I think my observation was based on older 
version of L1 implementation. This doesnt seem to be an issue with 
upstream L1. You may disable the kvm_enabled() path for now. I just 
tested and it works fine.

regards,
Harsh

> 
> regards,
> Harsh
> 
>>>       }
>>>   }
>>> @@ -735,6 +787,15 @@ SpaprCapabilityInfo 
>>> capability_table[SPAPR_CAP_NUM] = {
>>>           .type = "bool",
>>>           .apply = cap_nested_kvm_hv_apply,
>>>       },
>>> +    [SPAPR_CAP_NESTED_PAPR] = {
>>> +        .name = "nested-papr",
>>> +        .description = "Allow Nested HV (PAPR API)",
>>> +        .index = SPAPR_CAP_NESTED_PAPR,
>>> +        .get = spapr_cap_get_bool,
>>> +        .set = spapr_cap_set_bool,
>>> +        .type = "bool",
>>> +        .apply = cap_nested_papr_apply,
>>> +    },
>>>       [SPAPR_CAP_LARGE_DECREMENTER] = {
>>>           .name = "large-decr",
>>>           .description = "Allow Large Decrementer",
>>> @@ -919,6 +980,7 @@ SPAPR_CAP_MIG_STATE(sbbc, SPAPR_CAP_SBBC);
>>>   SPAPR_CAP_MIG_STATE(ibs, SPAPR_CAP_IBS);
>>>   SPAPR_CAP_MIG_STATE(hpt_maxpagesize, SPAPR_CAP_HPT_MAXPAGESIZE);
>>>   SPAPR_CAP_MIG_STATE(nested_kvm_hv, SPAPR_CAP_NESTED_KVM_HV);
>>> +SPAPR_CAP_MIG_STATE(nested_papr, SPAPR_CAP_NESTED_PAPR);
>>>   SPAPR_CAP_MIG_STATE(large_decr, SPAPR_CAP_LARGE_DECREMENTER);
>>>   SPAPR_CAP_MIG_STATE(ccf_assist, SPAPR_CAP_CCF_ASSIST);
>>>   SPAPR_CAP_MIG_STATE(fwnmi, SPAPR_CAP_FWNMI);
>>> diff --git a/hw/ppc/spapr_nested.c b/hw/ppc/spapr_nested.c
>>> index 597dba7fdc..8db9dc19e3 100644
>>> --- a/hw/ppc/spapr_nested.c
>>> +++ b/hw/ppc/spapr_nested.c
>>> @@ -13,13 +13,15 @@
>>>   void spapr_nested_reset(SpaprMachineState *spapr)
>>>   {
>>>       if (spapr_get_cap(spapr, SPAPR_CAP_NESTED_KVM_HV)) {
>>> -        spapr->nested.api = NESTED_API_KVM_HV;
>>>           spapr_unregister_nested_hv();
>>>           spapr_register_nested_hv();
>>> -    } else {
>>> -        spapr->nested.api = 0;
>>> +    } else if (spapr_get_cap(spapr, SPAPR_CAP_NESTED_PAPR)) {
>>>           spapr->nested.capabilities_set = false;
>>> +        spapr_unregister_nested_papr();
>>> +        spapr_register_nested_papr();
>>>           spapr_nested_gsb_init();
>>> +    } else {
>>> +        spapr->nested.api = 0;
>>>       }
>>>   }
>>