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

[Will Deacon]

On Tue, Apr 25, 2017 at 09:13:40AM +0530, Ganapatrao Kulkarni wrote:
> On Mon, Apr 24, 2017 at 9:15 PM, Will Deacon <will.deacon@xxxxxxx> wrote:
> > 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@xxxxxxx> 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@xxxxxxxxxx>
> >> >> ---
> >> >>
> >> >> 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.
> 
> okay, i can make exclude_hv visible only when kernel booted in EL2.
> is it ok to have empty directory "attr" when kernel booted to EL1?
> attr can be place holder for any other miscellaneous attributes, that
> can be added in future.

Sounds good to me, although I'll seek comment from the other perf folks
before merging anything with ABI implications.

Will