linux-kernel - Re: [PATCH 2/2] drivers/perf: riscv: Do not allow invalid raw event config

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Message-ID: <CAHBxVyF445KnZfT9rPhTwKA76_GT0eT3+p=ot1oLQzUb7j7d7w@mail.gmail.com>
Date: Wed, 11 Dec 2024 13:10:07 -0800
From: Atish Kumar Patra <atishp@...osinc.com>
To: Palmer Dabbelt <palmer@...belt.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>, atishp@...shpatra.org, anup@...infault.org, 
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, mchitale@...tanamicro.com, 
	samuel.holland@...ive.com, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drivers/perf: riscv: Do not allow invalid raw event config

On Wed, Dec 11, 2024 at 11:46 AM Palmer Dabbelt <palmer@...belt.com> wrote:
>
> On Mon, 09 Dec 2024 16:04:46 PST (-0800), Atish Patra wrote:
> > The SBI specification allows only lower 48bits of hpmeventX to be
> > configured via SBI PMU. Currently, the driver masks of the higher
> > bits but doesn't return an error. This will lead to an additional
> > SBI call for config matching which should return for an invalid
> > event error in most of the cases.
> >
> > However, if a platform(i.e Rocket and sifive cores) implements a
> > bitmap of all bits in the event encoding this will lead to an
> > incorrect event being programmed leading to user confusion.
> >
> > Report the error to the user if higher bits are set during the
> > event mapping itself to avoid the confusion and save an additional
> > SBI call.
> >
> > Suggested-by: Samuel Holland <samuel.holland@...ive.com>
> > Signed-off-by: Atish Patra <atishp@...osinc.com>
> > ---
> >  drivers/perf/riscv_pmu_sbi.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> > index 3473ba02abf3..fb6eda90f771 100644
> > --- a/drivers/perf/riscv_pmu_sbi.c
> > +++ b/drivers/perf/riscv_pmu_sbi.c
> > @@ -507,7 +507,7 @@ static int pmu_sbi_event_map(struct perf_event *event, u64 *econfig)
> >  {
> >       u32 type = event->attr.type;
> >       u64 config = event->attr.config;
> > -     int ret;
> > +     int ret = -ENOENT;
> >
> >       /*
> >        * Ensure we are finished checking standard hardware events for
> > @@ -536,8 +536,11 @@ static int pmu_sbi_event_map(struct perf_event *event, u64 *econfig)
> >
> >               switch (config >> 62) {
> >               case 0:
> > -                     ret = RISCV_PMU_RAW_EVENT_IDX;
> > -                     *econfig = config & RISCV_PMU_RAW_EVENT_MASK;
> > +                     /* Return error any bits [48-63] is set  as it is not allowed by the spec */
> > +                     if (!(config & ~RISCV_PMU_RAW_EVENT_MASK)) {
> > +                             *econfig = config & RISCV_PMU_RAW_EVENT_MASK;
> > +                             ret = RISCV_PMU_RAW_EVENT_IDX;
> > +                     }
> >                       break;
> >               case 2:
> >                       ret = (config & 0xFFFF) | (SBI_PMU_EVENT_TYPE_FW << 16);
> > @@ -554,7 +557,6 @@ static int pmu_sbi_event_map(struct perf_event *event, u64 *econfig)
> >               }
> >               break;
> >       default:
> > -             ret = -ENOENT;
> >               break;
> >       }
>
> This doesn't have a Fixes, is it
>
>     Fixes: f0c9363db2dd ("perf/riscv-sbi: Add platform specific firmware event handling")
>

I was not sure if a Fixes tag was worth it as the current
behavior(masking off the higher bits) is there from the beginning of
the driver.
perf tool throws a warning as well if a user tries to set any of the
upper 16 bits as event attributes is set to 0-47.

If it should be backported, this is the correct fixes tag.
Fixes: e9991434596f ("RISC-V: Add perf platform driver based on SBI
PMU extension")


> ?