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Message-ID: <CAOnJCUJCQjBfLZFW-3iLUB6ygyRmz1Anu+fhfrT4Lpoj2iNB5Q@mail.gmail.com>
Date: Mon, 1 Apr 2024 15:37:01 -0700
From: Atish Patra <atishp@...shpatra.org>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: Atish Patra <atishp@...osinc.com>, linux-kernel@...r.kernel.org,
Anup Patel <anup@...infault.org>, Albert Ou <aou@...s.berkeley.edu>,
Alexandre Ghiti <alexghiti@...osinc.com>, Conor Dooley <conor.dooley@...rochip.com>,
Guo Ren <guoren@...nel.org>, Icenowy Zheng <uwu@...nowy.me>, kvm-riscv@...ts.infradead.org,
kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-riscv@...ts.infradead.org, Mark Rutland <mark.rutland@....com>,
Palmer Dabbelt <palmer@...belt.com>, Paolo Bonzini <pbonzini@...hat.com>,
Paul Walmsley <paul.walmsley@...ive.com>, Shuah Khan <shuah@...nel.org>,
Will Deacon <will@...nel.org>
Subject: Re: [PATCH v4 07/15] RISC-V: KVM: No need to exit to the user space
if perf event failed
On Sat, Mar 2, 2024 at 12:16 AM Andrew Jones <ajones@...tanamicro.com> wrote:
>
> On Wed, Feb 28, 2024 at 05:01:22PM -0800, 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.
>
> I don't know enough about the perf subsystem to know if there may be
> a concern that resources are temporarily unavailable. If so, then this
Do you mean the hardware resources unavailable because the host is using it ?
> patch would make it possible for a guest to do the exact same thing,
> but sometimes succeed and sometimes get SBI_ERR_NOT_SUPPORTED.
> sbi_pmu_counter_config_matching doesn't currently have any error types
> specified that say "unsupported at the moment, maybe try again", which
> would be more appropriate in that case. I do see
> perf_event_create_kernel_counter() can return ENOMEM when memory isn't
> available, but if the kernel isn't able to allocate a small amount of
> memory, then we're in bigger trouble anyway, so the concern would be
> if there are perf resource pools which may temporarily be exhausted at
> the time the guest makes this request.
>
For other cases, this patch ensures that guests continue to run without failure
which allows the user in the guest to try again if this fails due to a temporary
resource availability.
> One comment below.
>
> >
> > Fixes: 0cb74b65d2e5 ("RISC-V: KVM: Implement perf support without sampling")
> > Reviewed-by: Anup Patel <anup@...infault.org>
> > Signed-off-by: Atish Patra <atishp@...osinc.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 b1574c043f77..29bf4ca798cb 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;
> > + 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
>
> Period after guest
>
>
> > + * operation can continue without profiling. Forward the
>
> The operation
>
Fixed the above two.
> > + * 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
> >
>
> Thanks,
> drew
--
Regards,
Atish
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