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

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Message-ID: <CAHBxVyH-2+Jj2vrqvYJBG0mHGLjCJM61DnpfT3H7pUoiFMpETA@mail.gmail.com>
Date: Thu, 12 Dec 2024 11:26:10 -0800
From: Atish Kumar Patra <atishp@...osinc.com>
To: Samuel Holland <samuel.holland@...ive.com>
Cc: Palmer Dabbelt <palmer@...belt.com>, 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, 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 8:06 PM Samuel Holland
<samuel.holland@...ive.com> wrote:
>
> Hi Atish,
>
> On 2024-12-11 3:10 PM, Atish Kumar Patra wrote:
> > 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")
>
> I would agree the masking isn't a real issue before changing the event attribute
> from 48 to 56 bits wide. However, this patch also does a drive-by fix of a
> different bug introduced by f0c9363db2dd: there is no "case 1" or default case,
> so the function would return an uninitialized value if the high bits are 01.
> Maybe that should be a separate patch, with a Fixes tag?
>

Good eye ;). I will split this one into two with a fixes tag for the
switch case.

> Regards,
> Samuel
>