Re: [PATCH v3 11/14] RISC-V: KVM: Implement trap & emulate for hpmcounters

[Anup Patel]

On Wed, Feb 1, 2023 at 2:29 PM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote:
>
> On Tue, Jan 31, 2023 at 2:46 PM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote:
> >
> > On Sun, Jan 29, 2023 at 4:44 AM Anup Patel <anup@xxxxxxxxxxxxxx> wrote:
> > >
> > > On Fri, Jan 27, 2023 at 11:56 PM Atish Patra <atishp@xxxxxxxxxxxx> wrote:
> > > >
> > > > As the KVM guests only see the virtual PMU counters, all hpmcounter
> > > > access should trap and KVM emulates the read access on behalf of guests.
> > > >
> > > > Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> > > > Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> > > > ---
> > > >  arch/riscv/include/asm/kvm_vcpu_pmu.h | 16 ++++++++++
> > > >  arch/riscv/kvm/vcpu_insn.c            |  4 ++-
> > > >  arch/riscv/kvm/vcpu_pmu.c             | 45 ++++++++++++++++++++++++++-
> > > >  3 files changed, 63 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/arch/riscv/include/asm/kvm_vcpu_pmu.h b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> > > > index 3f43a43..022d45d 100644
> > > > --- a/arch/riscv/include/asm/kvm_vcpu_pmu.h
> > > > +++ b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> > > > @@ -43,6 +43,19 @@ struct kvm_pmu {
> > > >  #define vcpu_to_pmu(vcpu) (&(vcpu)->arch.pmu)
> > > >  #define pmu_to_vcpu(pmu)  (container_of((pmu), struct kvm_vcpu, arch.pmu))
> > > >
> > > > +#if defined(CONFIG_32BIT)
> > > > +#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
> > > > +{ .base = CSR_CYCLEH,      .count = 31, .func = kvm_riscv_vcpu_pmu_read_hpm }, \
> > > > +{ .base = CSR_CYCLE,      .count = 31, .func = kvm_riscv_vcpu_pmu_read_hpm },
> > > > +#else
> > > > +#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
> > > > +{ .base = CSR_CYCLE,      .count = 31, .func = kvm_riscv_vcpu_pmu_read_hpm },
> > > > +#endif
> > > > +
> > > > +int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
> > > > +                               unsigned long *val, unsigned long new_val,
> > > > +                               unsigned long wr_mask);
> > > > +
> > > >  int kvm_riscv_vcpu_pmu_num_ctrs(struct kvm_vcpu *vcpu, struct kvm_vcpu_sbi_ext_data *edata);
> > > >  int kvm_riscv_vcpu_pmu_ctr_info(struct kvm_vcpu *vcpu, unsigned long cidx,
> > > >                                 struct kvm_vcpu_sbi_ext_data *edata);
> > > > @@ -65,6 +78,9 @@ void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu);
> > > >  #else
> > > >  struct kvm_pmu {
> > > >  };
> > > > +#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
> > > > +{ .base = 0,      .count = 0, .func = NULL },
> > > > +
> > >
> > > Redundant newline here.
> > >
> >
> > Fixed.
> >
> > > >
> > > >  static inline int kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
> > > >  {
> > > > diff --git a/arch/riscv/kvm/vcpu_insn.c b/arch/riscv/kvm/vcpu_insn.c
> > > > index 0bb5276..f689337 100644
> > > > --- a/arch/riscv/kvm/vcpu_insn.c
> > > > +++ b/arch/riscv/kvm/vcpu_insn.c
> > > > @@ -213,7 +213,9 @@ struct csr_func {
> > > >                     unsigned long wr_mask);
> > > >  };
> > > >
> > > > -static const struct csr_func csr_funcs[] = { };
> > > > +static const struct csr_func csr_funcs[] = {
> > > > +       KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS
> > > > +};
> > > >
> > > >  /**
> > > >   * kvm_riscv_vcpu_csr_return -- Handle CSR read/write after user space
> > > > diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> > > > index 7713927..894053a 100644
> > > > --- a/arch/riscv/kvm/vcpu_pmu.c
> > > > +++ b/arch/riscv/kvm/vcpu_pmu.c
> > > > @@ -17,6 +17,44 @@
> > > >
> > > >  #define kvm_pmu_num_counters(pmu) ((pmu)->num_hw_ctrs + (pmu)->num_fw_ctrs)
> > > >
> > > > +static int pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
> > > > +                       unsigned long *out_val)
> > > > +{
> > > > +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> > > > +       struct kvm_pmc *pmc;
> > > > +       u64 enabled, running;
> > > > +
> > > > +       pmc = &kvpmu->pmc[cidx];
> > > > +       if (!pmc->perf_event)
> > > > +               return -EINVAL;
> > > > +
> > > > +       pmc->counter_val += perf_event_read_value(pmc->perf_event, &enabled, &running);
> > > > +       *out_val = pmc->counter_val;
> > > > +
> > > > +       return 0;
> > > > +}
> > > > +
> > > > +int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
> > > > +                               unsigned long *val, unsigned long new_val,
> > > > +                               unsigned long wr_mask)
> > > > +{
> > > > +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> > > > +       int cidx, ret = KVM_INSN_CONTINUE_NEXT_SEPC;
> > > > +
> > > > +       if (!kvpmu || !kvpmu->init_done)
> > > > +               return KVM_INSN_EXIT_TO_USER_SPACE;
> > >
> > > As discussed previously, this should be KVM_INSN_ILLEGAL_TRAP.
> > >
>
> Thinking about it more, this results in a panic in guest S-mode which
> is probably undesirable.
> As per your earlier suggestion, we can return 0 for cycle/instret
> counters if accessed.
> This is only possible through legacy pmu drivers running in guests or
> some other OS that access any hpmcounters
> for random reasons.
>
> I think we should return KVM_INSN_ILLEGAL_TRAP for other counters and
> make the guest kernel panic.
> This does separate the behavior between fixed and programmable
> counters when everything is denied access in hcounteren.
>
> The new code will look like this:
>
> if (!kvpmu || !kvpmu->init_done) {
>     if (csr_num == CSR_CYCLE || csr_num == CSR_INSTRET) {
>         *val = 0;
>         return ret;
>     } else
>          return KVM_INSN_ILLEGAL_TRAP;
> }
>
> Let me know if you think otherwise.

Looks good to me. Please also add comment block inside
"if (!kvpmu || !kvpmu->init_done)"

>
> >
> > Done.
> > > > +
> > > > +       if (wr_mask)
> > > > +               return KVM_INSN_ILLEGAL_TRAP;
> > > > +
> > > > +       cidx = csr_num - CSR_CYCLE;
> > > > +
> > > > +       if (pmu_ctr_read(vcpu, cidx, val) < 0)
> > > > +               return KVM_INSN_EXIT_TO_USER_SPACE;
> > >
> > > Same as above.
> > >
>
> We can get rid of this as pmu_ctr_read doesn't return errors anyways.
>
> >
> > Done.
> >
> > > > +
> > > > +       return ret;
> > > > +}
> > > > +
> > > >  int kvm_riscv_vcpu_pmu_num_ctrs(struct kvm_vcpu *vcpu, struct kvm_vcpu_sbi_ext_data *edata)
> > > >  {
> > > >         struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> > > > @@ -69,7 +107,12 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
> > > >  int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
> > > >                                 struct kvm_vcpu_sbi_ext_data *edata)
> > > >  {
> > > > -       /* TODO */
> > > > +       int ret;
> > > > +
> > > > +       ret = pmu_ctr_read(vcpu, cidx, &edata->out_val);
> > > > +       if (ret == -EINVAL)
> > > > +               edata->err_val = SBI_ERR_INVALID_PARAM;
> > > > +
> > > >         return 0;
> > > >  }
> > > >
> > > > --
> > > > 2.25.1
> > > >
> > >
> > > Regards,
> > > Anup
> >
> >
> >
> > --
> > Regards,
> > Atish
>
>
>
> --
> Regards,
> Atish

Regards,
Anup