Re: [PATCH v5 11/22] RISC-V: KVM: No need to exit to the user space if perf event failed

From: Andrew Jones <ajones@ventanamicro.com>
To: Atish Patra <atishp@rivosinc.com>
Cc: linux-kernel@vger.kernel.org, Anup Patel <anup@brainfault.org>,
	 Ajay Kaher <akaher@vmware.com>,
	Alexandre Ghiti <alexghiti@rivosinc.com>,
	 Alexey Makhalov <amakhalov@vmware.com>,
	Conor Dooley <conor.dooley@microchip.com>,
	 Juergen Gross <jgross@suse.com>,
	kvm-riscv@lists.infradead.org, kvm@vger.kernel.org,
	 linux-kselftest@vger.kernel.org,
	linux-riscv@lists.infradead.org,
	 Mark Rutland <mark.rutland@arm.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	 Paolo Bonzini <pbonzini@redhat.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	 Shuah Khan <shuah@kernel.org>,
	virtualization@lists.linux.dev,
	 VMware PV-Drivers Reviewers <pv-drivers@vmware.com>,
	Will Deacon <will@kernel.org>,
	x86@kernel.org
Subject: Re: [PATCH v5 11/22] RISC-V: KVM: No need to exit to the user space if perf event failed
Date: Thu, 4 Apr 2024 14:19:30 +0200	[thread overview]
Message-ID: <20240404-de7d09060b134d467e437fcf@orel> (raw)
In-Reply-To: <20240403080452.1007601-12-atishp@rivosinc.com>

On Wed, Apr 03, 2024 at 01:04:40AM -0700, Atish Patra 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")
> Reviewed-by: Anup Patel <anup@brainfault.org>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  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 b5159ce4592d..2d9929bbc2c8 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;
>  
> @@ -454,7 +455,8 @@ 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);
> @@ -513,8 +515,10 @@ 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;

I'm still not sure about this. I replied in the v4 thread about it.

Thanks,
drew

> +			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..e1633606c98b 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.
> +		 * The 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
> 