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=-8.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 39A90C4363A for ; Thu, 22 Oct 2020 09:54:44 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 A1B3F223FB for ; Thu, 22 Oct 2020 09:54:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="MqumGfGo" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1B3F223FB 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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject: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=hzx2D8k1WGrqIhvz23UsReZY+9zdwnvwUSf6Fm7BjBs=; b=MqumGfGox0mU78kklnkZXWPXD fmnuMdafI+lPDUme0BSY4D3Lhe3M7OCrkjQ+IMTq5x888k0NToZtxHI6f/2ScEc/Ycj8dU331GZgF uEYjDyRruS7DlY+6S9KlSUVCJgmSyM1CrInK/yNzF1yLj/KrOL0mpquBD61wFFVKM27Ogr1v02+FH mT0cMcL1BiC+g4DzjCo4btKP7C/l80kqfvlLHOAzI1bbwiz/7dwQFWlIhEXhE1WZTMkulnVzqxlVS ZDZF4ubdUlB6NMsiFdU1bQ15NI9nEcxcRw6Nwc/FsIC8C7qL9msiQ0URBUwykWSpNW+XvbpW+5Amt 1pKi9wLqg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kVXHb-0007Lc-Pn; Thu, 22 Oct 2020 09:53:19 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kVXHX-0007KX-SI for linux-arm-kernel@lists.infradead.org; Thu, 22 Oct 2020 09:53:17 +0000 Received: from gaia (unknown [95.145.162.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C8BD1223FB; Thu, 22 Oct 2020 09:53:12 +0000 (UTC) Date: Thu, 22 Oct 2020 10:53:10 +0100 From: Catalin Marinas To: Will Deacon Subject: Re: [RFC PATCH v2 2/4] arm64: Add support for asymmetric AArch32 EL0 configurations Message-ID: <20201022095309.GD1229@gaia> References: <20201021104611.2744565-1-qais.yousef@arm.com> <20201021104611.2744565-3-qais.yousef@arm.com> <20201021153911.GC18071@willie-the-truck> <20201021162121.bdiopxvzscbhzzpt@e107158-lin> <20201021165246.GH3976@gaia> <20201021173859.GA18370@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201021173859.GA18370@willie-the-truck> 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-20201022_055316_083453_F8FFF179 X-CRM114-Status: GOOD ( 39.83 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, "Peter Zijlstra \(Intel\)" , Marc Zyngier , Morten Rasmussen , James Morse , Greg Kroah-Hartman , Linus Torvalds , Qais Yousef , linux-arm-kernel@lists.infradead.org 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, Oct 21, 2020 at 06:39:00PM +0100, Will Deacon wrote: > On Wed, Oct 21, 2020 at 05:52:47PM +0100, Catalin Marinas wrote: > > On Wed, Oct 21, 2020 at 05:21:21PM +0100, Qais Yousef wrote: > > > On 10/21/20 16:39, Will Deacon wrote: > > > > On Wed, Oct 21, 2020 at 11:46:09AM +0100, Qais Yousef wrote: > > > > > When the CONFIG_ASYMMETRIC_AARCH32 option is enabled (EXPERT), the type > > > > > of the ARM64_HAS_32BIT_EL0 capability becomes WEAK_LOCAL_CPU_FEATURE. > > > > > The kernel will now return true for system_supports_32bit_el0() and > > > > > checks 32-bit tasks are affined to AArch32 capable CPUs only in > > > > > do_notify_resume(). If the affinity contains a non-capable AArch32 CPU, > > > > > the tasks will get SIGKILLed. If the last CPU supporting 32-bit is > > > > > offlined, the kernel will SIGKILL any scheduled 32-bit tasks (the > > > > > alternative is to prevent offlining through a new .cpu_disable feature > > > > > entry). > > > > > > > > > > In addition to the relaxation of the ARM64_HAS_32BIT_EL0 capability, > > > > > this patch factors out the 32-bit cpuinfo and features setting into > > > > > separate functions: __cpuinfo_store_cpu_32bit(), > > > > > init_cpu_32bit_features(). The cpuinfo of the booting CPU > > > > > (boot_cpu_data) is now updated on the first 32-bit capable CPU even if > > > > > it is a secondary one. The ID_AA64PFR0_EL0_64BIT_ONLY feature is relaxed > > > > > to FTR_NONSTRICT and FTR_HIGHER_SAFE when the asymmetric AArch32 support > > > > > is enabled. The compat_elf_hwcaps are only verified for the > > > > > AArch32-capable CPUs to still allow hotplugging AArch64-only CPUs. > > > > > > > > > > Make sure that KVM never sees the asymmetric 32bit system. Guest can > > > > > still ignore ID registers and force run 32bit at EL0. > > > > > > > > > > Co-developed-by: Qais Yousef > > > > > Signed-off-by: Catalin Marinas > > > > > Signed-off-by: Qais Yousef > > > > > > > > [...] > > > > > > > > > diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h > > > > > index 5e784e16ee89..312974ab2c85 100644 > > > > > --- a/arch/arm64/include/asm/thread_info.h > > > > > +++ b/arch/arm64/include/asm/thread_info.h > > > > > @@ -67,6 +67,7 @@ void arch_release_task_struct(struct task_struct *tsk); > > > > > #define TIF_FOREIGN_FPSTATE 3 /* CPU's FP state is not current's */ > > > > > #define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */ > > > > > #define TIF_FSCHECK 5 /* Check FS is USER_DS on return */ > > > > > +#define TIF_CHECK_32BIT_AFFINITY 6 /* Check thread affinity for asymmetric AArch32 */ > > > > > > > > I've looked through the patch and I still can't figure out why this extra > > > > flag is needed. We know if a CPU supports 32-bit EL0, and we know whether > > > > or not a task is 32-bit. So why the extra flag? Is it just a hangover from > > > > the old series? > > > > > > It did evolve a bit organically. > > > > > > AFAICS it helps as an optimization to avoid the checks unnecessarily. If it's > > > not expensive to do the checks in the loop in do_notify_resume() we can omit > > > it. We will still protect it with system_supports_asym_32bit_el0() so the check > > > is done on these systems only. > > > > Ah, I think I remember now. We didn't want ret_to_user (entry.S) to > > always go the work_pending path if there was no context switch for a > > 32-bit task. With the AArch32 check in do_notify_resume(), it would mean > > we add _TIF_32BIT to the _TIF_WORK_MASK. > > > > However, we could add an asm alternative if AArch32 asym is detected to > > always route TIF_32BIT tasks to work_pending. > > Or could we just use TIF_NOTIFY_RESUME, like we for for rseq()? Maybe but it needs some analysis to make sure we don't lose this flag. It is cleared in some places. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel