Re: [PATCH v2 10/12] target/arm/cpu: spe: Enable spe to work with host cpu

[Haibo Xu]

On Tue, 8 Sep 2020 at 19:33, Andrew Jones <drjones@redhat.com> wrote:
>
> On Tue, Sep 08, 2020 at 08:13:28AM +0000, Haibo Xu wrote:
> > Turn on the spe cpu property by default if host cpu
> > support it, i.e. we can now do '-cpu max|host' to add
> > the vSPE, and '-cpu max|host,spe=off' to remove it.
> >
> > Signed-off-by: Haibo Xu <haibo.xu@linaro.org>
> > ---
> >  target/arm/cpu.c   |  3 +++
> >  target/arm/cpu.h   |  2 ++
> >  target/arm/cpu64.c |  7 ++++++-
> >  target/arm/kvm64.c | 12 ++++++++++++
> >  4 files changed, 23 insertions(+), 1 deletion(-)
> >
> > diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> > index 786cc6134c..58f12d6eb5 100644
> > --- a/target/arm/cpu.c
> > +++ b/target/arm/cpu.c
> > @@ -2271,6 +2271,9 @@ static void arm_host_initfn(Object *obj)
> >      kvm_arm_set_cpu_features_from_host(cpu);
> >      if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64)) {
> >          aarch64_add_sve_properties(obj);
> > +
> > +        cpu->has_spe = ON_OFF_AUTO_AUTO;
> > +        aarch64_add_spe_properties(obj);
>
> Why not put the assignment of has_spe into aarch64_add_spe_properties()?
>

Yes, it could be. Will fix it in v3.

> >      }
> >      arm_cpu_post_init(obj);
> >  }
> > diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> > index 395a1e5df8..5a3ea876c8 100644
> > --- a/target/arm/cpu.h
> > +++ b/target/arm/cpu.h
> > @@ -1040,6 +1040,7 @@ void aarch64_sve_narrow_vq(CPUARMState *env, unsigned 
> > vq);
> >  void aarch64_sve_change_el(CPUARMState *env, int old_el,
> >                             int new_el, bool el0_a64);
> >  void aarch64_add_sve_properties(Object *obj);
> > +void aarch64_add_spe_properties(Object *obj);
> >
> >  /*
> >   * SVE registers are encoded in KVM's memory in an endianness-invariant 
> > format.
> > @@ -1071,6 +1072,7 @@ static inline void aarch64_sve_change_el(CPUARMState 
> > *env, int o,
> >                                           int n, bool a)
> >  { }
> >  static inline void aarch64_add_sve_properties(Object *obj) { }
> > +static inline void aarch64_add_spe_properties(Object *obj) { }
> >  #endif
> >
> >  #if !defined(CONFIG_TCG)
> > diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
> > index 4997c4a3c0..d38c55e2ca 100644
> > --- a/target/arm/cpu64.c
> > +++ b/target/arm/cpu64.c
> > @@ -621,6 +621,11 @@ static void arm_spe_set(Object *obj, bool value, Error 
> > **errp)
> >      ARM_CPU(obj)->has_spe = value ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
> >  }
> >
> > +void aarch64_add_spe_properties(Object *obj)
> > +{
> > +    object_property_add_bool(obj, "spe", arm_spe_get, arm_spe_set);
> > +}
> > +
> >  /* -cpu max: if KVM is enabled, like -cpu host (best possible with this 
> > host);
> >   * otherwise, a CPU with as many features enabled as our emulation 
> > supports.
> >   * The version of '-cpu max' for qemu-system-arm is defined in cpu.c;
> > @@ -772,7 +777,7 @@ static void aarch64_max_initfn(Object *obj)
> >                          cpu_max_set_sve_max_vq, NULL, NULL);
> >
> >      cpu->has_spe = ON_OFF_AUTO_AUTO;
> > -    object_property_add_bool(obj, "spe", arm_spe_get, arm_spe_set);
> > +    aarch64_add_spe_properties(obj);
>
> If TCG doesn't support this cpu feature then this should be in the
> kvm_enabled() part of this function.
>
>

Will fix it in v3.

> >  }
> >
> >  static const ARMCPUInfo aarch64_cpus[] = {
> > diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> > index 5a2032fc9e..3f0a09c05b 100644
> > --- a/target/arm/kvm64.c
> > +++ b/target/arm/kvm64.c
> > @@ -515,6 +515,7 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures 
> > *ahcf)
> >       */
> >      int fdarray[3];
> >      bool sve_supported;
> > +    bool spe_supported;
> >      uint64_t features = 0;
> >      uint64_t t;
> >      int err;
> > @@ -655,6 +656,8 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures 
> > *ahcf)
> >      }
> >
> >      sve_supported = ioctl(fdarray[0], KVM_CHECK_EXTENSION, 
> > KVM_CAP_ARM_SVE) > 0;
> > +    spe_supported = ioctl(fdarray[0], KVM_CHECK_EXTENSION,
> > +                                      KVM_CAP_ARM_SPE_V1) > 0;
> >
> >      kvm_arm_destroy_scratch_host_vcpu(fdarray);
> >
> > @@ -668,6 +671,11 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures 
> > *ahcf)
> >          t = FIELD_DP64(t, ID_AA64PFR0, SVE, 1);
> >          ahcf->isar.id_aa64pfr0 = t;
> >      }
> > +    if (!spe_supported) {
> > +        t = ahcf->isar.id_aa64dfr0;
> > +        t = FIELD_DP64(t, ID_AA64DFR0, PMSVER, 0);
> > +        ahcf->isar.id_aa64dfr0 = t;
> > +    }
> >
>
> If this works then there's a bug with the KVM implementation. get-one-reg
> shouldn't expose SPE unless userspace has enabled it, which we're not
> doing on the scratch vcpu. That's why we set, not clear, the ID bits for
> SVE.
>
>

You are right. I have printed the returned field, and it's 0.
Thanks for pointing this out, I will fix it in v3.

Regards,
Haibo

> >      /*
> >       * We can assume any KVM supporting CPU is at least a v8
> > @@ -830,6 +838,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >          assert(kvm_arm_sve_supported());
> >          cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_SVE;
> >      }
> > +    if (cpu_isar_feature(aa64_spe, cpu)) {
> > +        assert(kvm_arm_spe_supported());
> > +        cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_SPE_V1;
> > +    }
> >
> >      /* Do KVM_ARM_VCPU_INIT ioctl */
> >      ret = kvm_arm_vcpu_init(cs);
> > --
> > 2.17.1
> >
>
> Thanks,
> drew
>