From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47774C433FE for ; Thu, 17 Nov 2022 05:45:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233725AbiKQFpV (ORCPT ); Thu, 17 Nov 2022 00:45:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233899AbiKQFpU (ORCPT ); Thu, 17 Nov 2022 00:45:20 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 847505EFB1; Wed, 16 Nov 2022 21:45:18 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2F71713D5; Wed, 16 Nov 2022 21:45:24 -0800 (PST) Received: from [10.162.40.18] (unknown [10.162.40.18]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 538693F73B; Wed, 16 Nov 2022 21:45:13 -0800 (PST) Message-ID: Date: Thu, 17 Nov 2022 11:15:10 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCH V5 6/7] arm64/perf: Add BRBE driver Content-Language: en-US To: James Clark Cc: Mark Brown , Rob Herring , Marc Zyngier , Suzuki Poulose , Ingo Molnar , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arm-kernel@lists.infradead.org, peterz@infradead.org, acme@kernel.org, mark.rutland@arm.com, will@kernel.org, catalin.marinas@arm.com References: <20221107062514.2851047-1-anshuman.khandual@arm.com> <20221107062514.2851047-7-anshuman.khandual@arm.com> <1d06f05c-0e7f-7648-6b1b-b78e999bc65f@arm.com> From: Anshuman Khandual In-Reply-To: <1d06f05c-0e7f-7648-6b1b-b78e999bc65f@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On 11/16/22 22:12, James Clark wrote: > > > On 07/11/2022 06:25, Anshuman Khandual wrote: > [...] > >> +static void perf_branch_to_brbcr(struct pmu_hw_events *cpuc, int branch_type) >> +{ >> + cpuc->brbcr = (BRBCR_EL1_CC | BRBCR_EL1_MPRED); >> + >> + if (branch_type & PERF_SAMPLE_BRANCH_USER) >> + cpuc->brbcr |= BRBCR_EL1_E0BRE; >> + >> + if (branch_type & PERF_SAMPLE_BRANCH_NO_CYCLES) >> + cpuc->brbcr &= ~BRBCR_EL1_CC; >> + >> + if (branch_type & PERF_SAMPLE_BRANCH_NO_FLAGS) >> + cpuc->brbcr &= ~BRBCR_EL1_MPRED; >> + >> + if (branch_type & PERF_SAMPLE_BRANCH_KERNEL) >> + cpuc->brbcr |= BRBCR_EL1_E1BRE; >> + else >> + return; >> + >> + /* >> + * The exception and exception return branches could be >> + * captured only when the event has necessary privilege >> + * indicated via branch type PERF_SAMPLE_BRANCH_KERNEL, >> + * which has been ascertained in generic perf. Please >> + * refer perf_copy_attr() for more details. >> + */ >> + if (branch_type & PERF_SAMPLE_BRANCH_ANY) { >> + cpuc->brbcr |= BRBCR_EL1_EXCEPTION; >> + cpuc->brbcr |= BRBCR_EL1_ERTN; > > Because this comes after the PERF_SAMPLE_BRANCH_KERNEL check, it's > impossible to get syscall records from userspace. When you enable kernel > branch records, the buffer always fills up before it gets to userspace. Just to summerize. System call [user_addr -> kernel_addr] and return [kernel_addr -> user_addr] records are impossible to be captured, because - Without PERF_SAMPLE_BRANCH_KERNEL, BRBCR_EL1_EXCEPTION/ERTN are not set - With PERF_SAMPLE_BRANCH_KERNEL, buffer fills up with in kernel branches Did you try with latest fix, that clears the paused BRBE after reading branch records during PMU interrupt ? That fix creates much more samples than before. > > Can you move this to the top so that it can be set if either > PERF_SAMPLE_BRANCH_USER or PERF_SAMPLE_BRANCH_KERNEL is set. The Why should they depend on privilege filters i.e PERF_SAMPLE_BRANCH_USER/KERNEL rather than just branch filters PERF_SAMPLE_BRANCH_ANY/ANY_CALL/ANY_RETURN ? > hardware already handles the security by giving partial records with the > kernel part zeroed out so I don't think the driver needs to add any > additional rules other than setting BRBCR_EL1_E1BRE or BRBCR_EL1_E0BRE. Basically BRBCR_EL1_EXCEPTION/BRBCR_EL1_ERTN should be treated like any other branch filter rather than privilege filters as is the case now ? > > For example I moved it to the top, removed the return below and then I > get syscall partial records: > > .... 5: 0000000000745d0c -> 0000000000000000 0 cycles P 9fbfbfbf SYSCALL > > I also get ERETS but with only the userspace part set: > > ..... 4: 0000000000000000 -> 0000000000745d10 0 cycles P 9fbfbfbf ERET But with both user and kernel privilege filters being set, these should have been complete branch records containing both user and kernel addresses ? > >> + return; >> + } >> + >> + if (branch_type & PERF_SAMPLE_BRANCH_ANY_CALL) >> + cpuc->brbcr |= BRBCR_EL1_EXCEPTION; >> + >> + if (branch_type & PERF_SAMPLE_BRANCH_ANY_RETURN) >> + cpuc->brbcr |= BRBCR_EL1_ERTN; >> +} >> + [....]