From patchwork Mon Oct 16 10:24:42 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 13422953 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 6BE74CDB474 for ; Mon, 16 Oct 2023 10:27:58 +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:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=szRVrCYprE0N3vC6ioq9D/hwLTP5nSgmYAX9DGha0oA=; b=XeNTIjBLzgkwht 0k1mXbKhyYh7gdM8YgwjRz+L8+UQ1fnfDBlCQhuXyfgFMcdj9sfe/iglSS//Y7kWxG6/aHV3nVep0 kCU4fTRIaKfxsiMaCizpWE9IuOhfroj9WMEd7YqWMHdrhXDWU6C3N5WSbBu3ZV8QGSelouG2anN7C Go3ZUITA9GEl816tVILFRVZVmKc6VmG5pGzN6jnAJIVb/YCGkUWl5YnFx4pUH1FWMzpgD5DshZGTr Hhv7l9VOA94AW4WI60/CPmV13X5BxX5m585kkWqG3frL6WncnSK1z+X7KeiE7q9LNLwWtnFnjCdbv GEdHx8PMcawgYjPrrTiQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qsKon-009Gfr-2u; Mon, 16 Oct 2023 10:27:25 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qsKnf-009FUv-1r for linux-arm-kernel@lists.infradead.org; Mon, 16 Oct 2023 10:26:17 +0000 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 D912C1FB; Mon, 16 Oct 2023 03:26:54 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 1190E3F762; Mon, 16 Oct 2023 03:26:11 -0700 (PDT) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: ardb@kernel.org, bertrand.marquis@arm.com, boris.ostrovsky@oracle.com, broonie@kernel.org, catalin.marinas@arm.com, daniel.lezcano@linaro.org, james.morse@arm.com, jgross@suse.com, kristina.martsenko@arm.com, mark.rutland@arm.com, maz@kernel.org, oliver.upton@linux.dev, pcc@google.com, sstabellini@kernel.org, suzuki.poulose@arm.com, tglx@linutronix.de, vladimir.murzin@arm.com, will@kernel.org Subject: [PATCH v4 19/38] arm64: Avoid cpus_have_const_cap() for ARM64_HAS_DIT Date: Mon, 16 Oct 2023 11:24:42 +0100 Message-Id: <20231016102501.3643901-20-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20231016102501.3643901-1-mark.rutland@arm.com> References: <20231016102501.3643901-1-mark.rutland@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231016_032615_725299_25C884A2 X-CRM114-Status: GOOD ( 20.21 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org In __cpu_suspend_exit() we use cpus_have_const_cap() to check for ARM64_HAS_DIT but this is not necessary and cpus_have_final_cap() of alternative_has_cap_*() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. The ARM64_HAS_DIT cpucap is detected and patched (along with all other cpucaps) before __cpu_suspend_exit() can run. We'll only use __cpu_suspend_exit() as part of PSCI cpuidle or hibernation, and both of these are intialized after system cpucaps are detected and patched: the PSCI cpuidle driver is registered with a device_initcall, hibernation restoration occurs in a late_initcall, and hibarnation saving is driven by usrspace. Therefore it is not necessary to use cpus_have_const_cap(), and using alternative_has_cap_*() or cpus_have_final_cap() is sufficient. This patch replaces the use of cpus_have_const_cap() with alternative_has_cap_unlikely(), which will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. To clearly document the ordering relationship between suspend/resume and alternatives patching, an explicit check for system_capabilities_finalized() is added to cpu_suspend() along with a comment block, which will make it easier to spot issues if code is changed in future to allow these functions to be reached earlier. Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: James Morse Cc: Suzuki K Poulose Cc: Will Deacon --- arch/arm64/kernel/suspend.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c index c09fa99e0a44e..eca4d04352118 100644 --- a/arch/arm64/kernel/suspend.c +++ b/arch/arm64/kernel/suspend.c @@ -61,7 +61,7 @@ void notrace __cpu_suspend_exit(void) * PSTATE was not saved over suspend/resume, re-enable any detected * features that might not have been set correctly. */ - if (cpus_have_const_cap(ARM64_HAS_DIT)) + if (alternative_has_cap_unlikely(ARM64_HAS_DIT)) set_pstate_dit(1); __uaccess_enable_hw_pan(); @@ -98,6 +98,15 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long)) struct sleep_stack_data state; struct arm_cpuidle_irq_context context; + /* + * Some portions of CPU state (e.g. PSTATE.{PAN,DIT}) are initialized + * before alternatives are patched, but are only restored by + * __cpu_suspend_exit() after alternatives are patched. To avoid + * accidentally losing these bits we must not attempt to suspend until + * after alternatives have been patched. + */ + WARN_ON(!system_capabilities_finalized()); + /* Report any MTE async fault before going to suspend */ mte_suspend_enter();