Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1433241AbdDZGxu (ORCPT ); Wed, 26 Apr 2017 02:53:50 -0400 Received: from mail-it0-f65.google.com ([209.85.214.65]:36729 "EHLO mail-it0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1433218AbdDZGxl (ORCPT ); Wed, 26 Apr 2017 02:53:41 -0400 MIME-Version: 1.0 In-Reply-To: <20170425165259.GS24484@arm.com> References: <1492623846-29335-1-git-send-email-ganapatrao.kulkarni@cavium.com> <20170420084928.GC31436@leverpostej> <20170424154530.GO12323@arm.com> <20170425165259.GS24484@arm.com> From: "Jayachandran C." Date: Wed, 26 Apr 2017 12:23:39 +0530 Message-ID: Subject: Re: [PATCH v2] arm64: perf: Use only exclude_kernel attribute when kernel is running in HYP To: Will Deacon Cc: Ganapatrao Kulkarni , Mark Rutland , "Andrew.Pinski@caviumnetworks.com" , Catalin Marinas , "linux-kernel@vger.kernel.org" , acme@kernel.org, alexander.shishkin@linux.intel.com, peterz@infradead.org, Ingo Molnar , jnair@caviumnetworks.com, Ganapatrao Kulkarni , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3931 Lines: 85 Hi Will, On Tue, Apr 25, 2017 at 10:23 PM, Will Deacon wrote: > On Tue, Apr 25, 2017 at 09:13:40AM +0530, Ganapatrao Kulkarni wrote: >> On Mon, Apr 24, 2017 at 9:15 PM, Will Deacon 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 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 >> >> >> --- >> >> >> >> >> >> 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. Do you really think this is the solution given: - this is an arm64 specific sysfs interface that is tied to the perf API - the perf API documentation has to be updated for this - All the applications that use the perf API have to be modified to check this sysfs interface - If the application fails to do so, a very narrow corner case (exclude_hv != exclude_kernel and VHE enabled) fails. Any application that really cares can already do see if exclude_hv != exclude_kernel case works by calling perf_open_event() with those options and checking the return value. Hope I am mistake here, otherwise this does not sound like a good idea. JC.