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 X-Spam-Level: X-Spam-Status: No, score=-15.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 899E0C48BE6 for ; Mon, 14 Jun 2021 17:11:04 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 4EE17611CA for ; Mon, 14 Jun 2021 17:11:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4EE17611CA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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=TFl54IAaQc7WsXJBZzb6E478a8zXWTRou9wtfvFHpW8=; b=nP92MmSZ5jwi9i SN7YmOrJgU6WVtweV9yfQZmYB7Fi28rNjVYznaoWPkGwE0dLUxq+k+vPo4Yh0e9poU8e07/KHof1V 7Ph2GNKPT3qYNdlZU+8o7/Qr/sEOa7+ZzjniNehwfpDmXPtchA7yHNVB9X90+ENdEeYzILoHLoIxh 8t8/vWtQ7LXvvESLjthkqSPB8FTGMTgNVC7vcFwSI1nD9nJv8Tr1s85etN1fIdDo2i+QqhfPcBQCb MgwifKtRDEaOmklX5pI7pr3xqMrlSrEu22rKsSebq4WXY+2Jdtwklh7hZXmRfhaqSzmNbMSqZRT+n 8y6YGWN+Y8H0AcJCC0YQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lsq59-00FKGQ-SH; Mon, 14 Jun 2021 17:09:04 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1lsq3h-00FJmL-AS for linux-arm-kernel@lists.infradead.org; Mon, 14 Jun 2021 17:07:35 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id C05C461185; Mon, 14 Jun 2021 17:07:31 +0000 (UTC) Date: Mon, 14 Jun 2021 18:07:29 +0100 From: Catalin Marinas To: Yu Zhao Cc: Jia He , Mark Rutland , Will Deacon , Marc Zyngier , Suzuki Poulose , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] arm64: mm: fix warning in arch_faults_on_old_pte() Message-ID: <20210614170727.GG30667@arm.com> References: <20210613214728.1695340-1-yuzhao@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210613214728.1695340-1-yuzhao@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210614_100733_431124_8F59517B X-CRM114-Status: GOOD ( 20.45 ) 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 Sun, Jun 13, 2021 at 03:47:28PM -0600, Yu Zhao wrote: > cow_user_page() doesn't disable preemption, and it triggers the > warning in arch_faults_on_old_pte() when CONFIG_PREEMPT_COUNT=y. I'm surprised we haven't seen this warning until now. We probably haven't exercised this path with the right config options. > Converting the Access flag support to a system-wide feature to avoid > reading ID_AA64MMFR1_EL1 on local CPUs when determining the h/w cap. > > Note that though the Access flag support is a non-conflicting feature, > we require all late CPUs to have it if the boot CPU does. Otherwise > the feature won't be enabled regardless of the capabilities of late > CPUs. > > If there are h/w implementations that break this rule, they will have > to add errata, unless they can provide justifications to switch to the > less strict ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE. > > Signed-off-by: Yu Zhao I'm ok in principle but one small issue below. > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index efed2830d141..afdb6e0336ed 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1566,6 +1566,14 @@ static bool has_hw_dbm(const struct arm64_cpu_capabilities *cap, > return true; > } > > +static void cpu_enable_hw_af(struct arm64_cpu_capabilities const *cap) > +{ > + if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU)) { > + u64 val = read_sysreg(tcr_el1); > + > + write_sysreg(val | TCR_HA, tcr_el1); > + } > +} This needs an isb(); local_flush_tlb_all() since this bit may be cached in the TLB. See how we did it in __cpu_enable_hw_dbm(). Alternatively you could leave the current TCR_AF bit setting as is (in proc.S) and only add an arm64_features[] entry for AF together with the arch_faults_on_old_pte() change but without any enable function. I'm not sure we have mixed CPUs where only some of them support AF to benefit from this. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel