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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1C85DC43219 for ; Wed, 9 Feb 2022 18:14:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=oZQ+I3JHy+OKGm3KEtUABEt4sKxCkaG3Cn1tpicaOG8=; b=co3VxK1d5k+BjS BFPUjI4navvCGs8lM4Fd2LQEYf7oNQWIdttJ5e/re35Kg0XaO8yjSVQtlG1E5PRWJ6Ns3bU52hKmq fUvULE9gEOxk5tWaBcPPAJPNfcGblB8WgdH6S6h0soajc5L1alRRI0nR/CznRL49HNeYldNbls576 O/fR+fbcsWY0LFk1FF/PqKa5KByssN2Qi9eoz9wTnlYJdSWKJ75KNdNHVioqtwQ3znwIh0X3Js55Q N/pTlCKdkp4Zaa454WmRCrXwtVxkA5BKNgRS7yd+zkY92jgou9zf5KE+sULvxPcctcHY/VNczLRhN r/J4pvWIcwc/hlwXAelw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nHrTS-0015QT-8E; Wed, 09 Feb 2022 18:13:50 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nHrTO-0015PF-Kd for linux-arm-kernel@lists.infradead.org; Wed, 09 Feb 2022 18:13:47 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 02C6661B89; Wed, 9 Feb 2022 18:13:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F01CCC340E7; Wed, 9 Feb 2022 18:13:42 +0000 (UTC) Date: Wed, 9 Feb 2022 18:13:39 +0000 From: Catalin Marinas To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, ardb@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, frederic@kernel.org, james.morse@arm.com, joey.gouly@arm.com, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, valentin.schneider@arm.com, will@kernel.org Subject: Re: [PATCH v3 7/7] arm64: support PREEMPT_DYNAMIC Message-ID: References: <20220209153535.818830-1-mark.rutland@arm.com> <20220209153535.818830-8-mark.rutland@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220209153535.818830-8-mark.rutland@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220209_101346_722618_9379BE1D X-CRM114-Status: GOOD ( 21.26 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Feb 09, 2022 at 03:35:35PM +0000, Mark Rutland wrote: > This patch enables support for PREEMPT_DYNAMIC on arm64, allowing the > preemption model to be chosen at boot time. > > Specifically, this patch selects HAVE_PREEMPT_DYNAMIC_KEY, so that each > preemption function is an out-of-line call with an early return > depending upon a static key. This leaves almost all the codegen up to > the compiler, and side-steps a number of pain points with static calls > (e.g. interaction with CFI schemes). This should have no worse overhead > than using non-inline static calls, as those use out-of-line trampolines > with early returns. > > For example, the dynamic_cond_resched() wrapper looks as follows when > enabled. When disabled, the first `B` is replaced with a `NOP`, > resulting in an early return. > > | : > | bti c > | b // or `nop` > | mov w0, #0x0 > | ret > | mrs x0, sp_el0 > | ldr x0, [x0, #8] > | cbnz x0, > | paciasp > | stp x29, x30, [sp, #-16]! > | mov x29, sp > | bl > | mov w0, #0x1 > | ldp x29, x30, [sp], #16 > | autiasp > | ret > > ... compared to the regular form of the function: > > | <__cond_resched>: > | bti c > | mrs x0, sp_el0 > | ldr x1, [x0, #8] > | cbz x1, <__cond_resched+0x18> > | mov w0, #0x0 > | ret > | paciasp > | stp x29, x30, [sp, #-16]! > | mov x29, sp > | bl > | mov w0, #0x1 > | ldp x29, x30, [sp], #16 > | autiasp > | ret > > Since arm64 does not yet use the generic entry code, we must define our > own `sk_dynamic_irqentry_exit_cond_resched`, which will be > enabled/disabled by the common code in kernel/sched/core.c. All other > preemption functions and associated static keys are defined there. > > Note that PREEMPT_DYNAMIC is `def bool y`, so this will default to > enabled. > > Signed-off-by: Mark Rutland > Cc: Ard Biesheuvel > Cc: Catalin Marinas > Cc: Frederic Weisbecker > Cc: Ingo Molnar > Cc: Joey Gouly > Cc: Juri Lelli > Cc: Peter Zijlstra > Cc: Valentin Schneider > Cc: Will Deacon Acked-by: Catalin Marinas _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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 C720CC433F5 for ; Wed, 9 Feb 2022 18:17:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239583AbiBISR3 (ORCPT ); Wed, 9 Feb 2022 13:17:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239224AbiBISRP (ORCPT ); Wed, 9 Feb 2022 13:17:15 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EE6C6C0045C2 for ; Wed, 9 Feb 2022 10:14:15 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 0A7FFB82379 for ; Wed, 9 Feb 2022 18:13:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F01CCC340E7; Wed, 9 Feb 2022 18:13:42 +0000 (UTC) Date: Wed, 9 Feb 2022 18:13:39 +0000 From: Catalin Marinas To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, ardb@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, frederic@kernel.org, james.morse@arm.com, joey.gouly@arm.com, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, valentin.schneider@arm.com, will@kernel.org Subject: Re: [PATCH v3 7/7] arm64: support PREEMPT_DYNAMIC Message-ID: References: <20220209153535.818830-1-mark.rutland@arm.com> <20220209153535.818830-8-mark.rutland@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220209153535.818830-8-mark.rutland@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 09, 2022 at 03:35:35PM +0000, Mark Rutland wrote: > This patch enables support for PREEMPT_DYNAMIC on arm64, allowing the > preemption model to be chosen at boot time. > > Specifically, this patch selects HAVE_PREEMPT_DYNAMIC_KEY, so that each > preemption function is an out-of-line call with an early return > depending upon a static key. This leaves almost all the codegen up to > the compiler, and side-steps a number of pain points with static calls > (e.g. interaction with CFI schemes). This should have no worse overhead > than using non-inline static calls, as those use out-of-line trampolines > with early returns. > > For example, the dynamic_cond_resched() wrapper looks as follows when > enabled. When disabled, the first `B` is replaced with a `NOP`, > resulting in an early return. > > | : > | bti c > | b // or `nop` > | mov w0, #0x0 > | ret > | mrs x0, sp_el0 > | ldr x0, [x0, #8] > | cbnz x0, > | paciasp > | stp x29, x30, [sp, #-16]! > | mov x29, sp > | bl > | mov w0, #0x1 > | ldp x29, x30, [sp], #16 > | autiasp > | ret > > ... compared to the regular form of the function: > > | <__cond_resched>: > | bti c > | mrs x0, sp_el0 > | ldr x1, [x0, #8] > | cbz x1, <__cond_resched+0x18> > | mov w0, #0x0 > | ret > | paciasp > | stp x29, x30, [sp, #-16]! > | mov x29, sp > | bl > | mov w0, #0x1 > | ldp x29, x30, [sp], #16 > | autiasp > | ret > > Since arm64 does not yet use the generic entry code, we must define our > own `sk_dynamic_irqentry_exit_cond_resched`, which will be > enabled/disabled by the common code in kernel/sched/core.c. All other > preemption functions and associated static keys are defined there. > > Note that PREEMPT_DYNAMIC is `def bool y`, so this will default to > enabled. > > Signed-off-by: Mark Rutland > Cc: Ard Biesheuvel > Cc: Catalin Marinas > Cc: Frederic Weisbecker > Cc: Ingo Molnar > Cc: Joey Gouly > Cc: Juri Lelli > Cc: Peter Zijlstra > Cc: Valentin Schneider > Cc: Will Deacon Acked-by: Catalin Marinas