linux-kernel - Re: [v2 07/10] RISC-V: KVM: No need to exit to the user space if perf event failed

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Message-ID: <CAAhSdy1cb_bEuE+pHusEoumhteu=Y87+WXpE=Eox1k2ng4pdZg@mail.gmail.com>
Date: Sat, 30 Dec 2023 13:31:36 +0530
From: Anup Patel <anup@...infault.org>
To: Atish Patra <atishp@...osinc.com>
Cc: linux-kernel@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>, 
	Alexandre Ghiti <alexghiti@...osinc.com>, Andrew Jones <ajones@...tanamicro.com>, 
	Atish Patra <atishp@...shpatra.org>, Conor Dooley <conor.dooley@...rochip.com>, 
	Guo Ren <guoren@...nel.org>, Heiko Stuebner <heiko@...ech.de>, kvm-riscv@...ts.infradead.org, 
	kvm@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	Mark Rutland <mark.rutland@....com>, Palmer Dabbelt <palmer@...belt.com>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Will Deacon <will@...nel.org>
Subject: Re: [v2 07/10] RISC-V: KVM: No need to exit to the user space if perf
 event failed

On Sat, Dec 30, 2023 at 3:20 AM Atish Patra <atishp@...osinc.com> wrote:
>
> Currently, we return a linux error code if creating a perf event failed
> in kvm. That shouldn't be necessary as guest can continue to operate
> without perf profiling or profiling with firmware counters.
>
> Return appropriate SBI error code to indicate that PMU configuration
> failed. An error message in kvm already describes the reason for failure.
>
> Fixes: 0cb74b65d2e5 ("RISC-V: KVM: Implement perf support without sampling")
> Signed-off-by: Atish Patra <atishp@...osinc.com>

LGTM.

Reviewed-by: Anup Patel <anup@...infault.org>

Regards,
Anup

> ---
>  arch/riscv/kvm/vcpu_pmu.c     | 14 +++++++++-----
>  arch/riscv/kvm/vcpu_sbi_pmu.c |  6 +++---
>  2 files changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index 8c44f26e754d..08f561998611 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -229,8 +229,9 @@ static int kvm_pmu_validate_counter_mask(struct kvm_pmu *kvpmu, unsigned long ct
>         return 0;
>  }
>
> -static int kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_attr *attr,
> -                                    unsigned long flags, unsigned long eidx, unsigned long evtdata)
> +static long kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_attr *attr,
> +                                     unsigned long flags, unsigned long eidx,
> +                                     unsigned long evtdata)
>  {
>         struct perf_event *event;
>
> @@ -455,7 +456,8 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
>                                      unsigned long eidx, u64 evtdata,
>                                      struct kvm_vcpu_sbi_return *retdata)
>  {
> -       int ctr_idx, ret, sbiret = 0;
> +       int ctr_idx, sbiret = 0;
> +       long ret;
>         bool is_fevent;
>         unsigned long event_code;
>         u32 etype = kvm_pmu_get_perf_event_type(eidx);
> @@ -514,8 +516,10 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
>                         kvpmu->fw_event[event_code].started = true;
>         } else {
>                 ret = kvm_pmu_create_perf_event(pmc, &attr, flags, eidx, evtdata);
> -               if (ret)
> -                       return ret;
> +               if (ret) {
> +                       sbiret = SBI_ERR_NOT_SUPPORTED;
> +                       goto out;
> +               }
>         }
>
>         set_bit(ctr_idx, kvpmu->pmc_in_use);
> diff --git a/arch/riscv/kvm/vcpu_sbi_pmu.c b/arch/riscv/kvm/vcpu_sbi_pmu.c
> index 7eca72df2cbd..b70179e9e875 100644
> --- a/arch/riscv/kvm/vcpu_sbi_pmu.c
> +++ b/arch/riscv/kvm/vcpu_sbi_pmu.c
> @@ -42,9 +42,9 @@ static int kvm_sbi_ext_pmu_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  #endif
>                 /*
>                  * This can fail if perf core framework fails to create an event.
> -                * Forward the error to userspace because it's an error which
> -                * happened within the host kernel. The other option would be
> -                * to convert to an SBI error and forward to the guest.
> +                * No need to forward the error to userspace and exit the guest
> +                * operation can continue without profiling. Forward the
> +                * appropriate SBI error to the guest.
>                  */
>                 ret = kvm_riscv_vcpu_pmu_ctr_cfg_match(vcpu, cp->a0, cp->a1,
>                                                        cp->a2, cp->a3, temp, retdata);
> --
> 2.34.1
>