linux-kernel - Re: [PATCH v2] arm64: perf: Use only exclude_kernel attribute when kernel is running in HYP

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Date:   Mon, 24 Apr 2017 16:45:30 +0100
From:   Will Deacon <will.deacon@....com>
To:     Ganapatrao Kulkarni <gpkulkarni@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        "Andrew.Pinski@...iumnetworks.com" <Andrew.Pinski@...iumnetworks.com>,
        Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, peterz@...radead.org,
        Ingo Molnar <mingo@...hat.com>, jnair@...iumnetworks.com
Subject: Re: [PATCH v2] arm64: perf: Use only exclude_kernel attribute when
 kernel is running in HYP

On Thu, Apr 20, 2017 at 02:56:50PM +0530, Ganapatrao Kulkarni wrote:
> On Thu, Apr 20, 2017 at 2:19 PM, Mark Rutland <mark.rutland@....com> wrote:
> > On Wed, Apr 19, 2017 at 11:14:06PM +0530, Ganapatrao Kulkarni wrote:
> >> commit d98ecda (arm64: perf: Count EL2 events if the kernel is running in HYP)
> >> is returning error for perf syscall with mixed attribute set for exclude_kernel
> >> and exclude_hv. This change is breaking some applications (observed with hhvm)
> >> when ran on VHE enabled platforms.
> >>
> >> Adding fix to consider only exclude_kernel attribute when kernel is
> >> running in HYP. Also adding sysfs file to notify the bhehaviour
> >> of attribute exclude_hv.
> >>
> >> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
> >> ---
> >>
> >> Changelog:
> >>
> >> V2:
> >>  - Changes as per Will Deacon's suggestion.
> >>
> >> V1: Initial patch
> >>
> >>  arch/arm64/kernel/perf_event.c | 28 ++++++++++++++++++++++++----
> >>  include/linux/perf/arm_pmu.h   |  1 +
> >>  2 files changed, 25 insertions(+), 4 deletions(-)
> >>
> >> @@ -871,14 +890,13 @@ static int armv8pmu_set_event_filter(struct hw_perf_event *event,
> >>
> >>       if (attr->exclude_idle)
> >>               return -EPERM;
> >> -     if (is_kernel_in_hyp_mode() &&
> >> -         attr->exclude_kernel != attr->exclude_hv)
> >> -             return -EINVAL;
> >> +     if (is_kernel_in_hyp_mode() && !attr->exclude_kernel)
> >> +             config_base |= ARMV8_PMU_INCLUDE_EL2;
> >>       if (attr->exclude_user)
> >>               config_base |= ARMV8_PMU_EXCLUDE_EL0;
> >>       if (!is_kernel_in_hyp_mode() && attr->exclude_kernel)
> >>               config_base |= ARMV8_PMU_EXCLUDE_EL1;
> >> -     if (!attr->exclude_hv)
> >> +     if (!is_kernel_in_hyp_mode() && !attr->exclude_hv)
> >>               config_base |= ARMV8_PMU_INCLUDE_EL2;
> >
> > This isn't quite what Will suggested.
> >
> > The idea was that userspace would read sysfs, then use that to determine
> > the correct exclusion parameters [1,2]. This logic was not expected to
> > change; it correctly validates whether we can provide what the user
> > requests.
> 
> OK, if you are ok with sysfs part, i can send next version with that
> change only?.

I think the sysfs part is still a little dodgy, since you still expose the
"exclude_hv" file with a value of 0 when not running at EL2, which would
imply that exclude_hv is forced to zero. I don't think that's correct.

Will