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=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,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 BF6F9C433E7 for ; Fri, 9 Oct 2020 08:40:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8245622276 for ; Fri, 9 Oct 2020 08:40:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602232814; bh=3FnNRrdFZy8dpkVRh9duQr65KKRLcp5XuZqmODbiGFI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=x9G334LD6lRdjtmnClFaMvlPCMy49TRBA79+ZrR695flRzN0w0vK437DOzuFqD85d go9XWtgwHM+L9V+qst6IKu1z/NsHM0csUmF9f236slOb3RA1FA2F/HhnF+eYxcidTx EUnqxRSu0v936HJugZWYwCGpe5wHDP0w/Lk7y4FA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732555AbgJIIkO (ORCPT ); Fri, 9 Oct 2020 04:40:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:49272 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729347AbgJIIkO (ORCPT ); Fri, 9 Oct 2020 04:40:14 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 3C3A12087D; Fri, 9 Oct 2020 08:40:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602232812; bh=3FnNRrdFZy8dpkVRh9duQr65KKRLcp5XuZqmODbiGFI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DMeSUc9JZDrvNMltlX3QyR/dLxuPDyT2wQ+MEhojEqCyMgsTc5n3+Gi3/7Eh3bQis XZtZdASUjMV37MkDMtvIXGfeAnmy1MeFniAk617NWFq4v/O0+lbL2KBSdBliNIT5yQ jcyk1TQItgRC5flgX9F2GhlE2kG2sMHvb2/ropu4= Date: Fri, 9 Oct 2020 09:40:07 +0100 From: Will Deacon To: Greg Kroah-Hartman Cc: Qais Yousef , Catalin Marinas , Marc Zyngier , "Peter Zijlstra (Intel)" , Morten Rasmussen , Linus Torvalds , linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org Subject: Re: [RFC PATCH 2/3] arm64: Add support for asymmetric AArch32 EL0 configurations Message-ID: <20201009084007.GB29594@willie-the-truck> References: <20201008181641.32767-1-qais.yousef@arm.com> <20201008181641.32767-3-qais.yousef@arm.com> <20201009061356.GA120580@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201009061356.GA120580@kroah.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Fri, Oct 09, 2020 at 08:13:56AM +0200, Greg Kroah-Hartman wrote: > On Thu, Oct 08, 2020 at 07:16:40PM +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 > > --- > > arch/arm64/Kconfig | 14 ++++++ > > arch/arm64/include/asm/cpu.h | 2 + > > arch/arm64/include/asm/cpucaps.h | 3 +- > > arch/arm64/include/asm/cpufeature.h | 20 +++++++- > > arch/arm64/include/asm/thread_info.h | 5 +- > > arch/arm64/kernel/cpufeature.c | 66 +++++++++++++++----------- > > arch/arm64/kernel/cpuinfo.c | 71 ++++++++++++++++++---------- > > arch/arm64/kernel/process.c | 17 +++++++ > > arch/arm64/kernel/signal.c | 18 +++++++ > > arch/arm64/kvm/arm.c | 5 +- > > arch/arm64/kvm/guest.c | 2 +- > > arch/arm64/kvm/sys_regs.c | 14 +++++- > > 12 files changed, 176 insertions(+), 61 deletions(-) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index 6d232837cbee..591853504dc4 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -1868,6 +1868,20 @@ config DMI > > > > endmenu > > > > +config ASYMMETRIC_AARCH32 > > + bool "Allow support for asymmetric AArch32 support" > > + depends on COMPAT && EXPERT > > Why EXPERT? You don't want this able to be enabled by anyone? TBH, I'd be inclined to drop the Kconfig option altogether. We're not looking at a lot of code here, so all it does is further fragment the build testing we get from CI (or it just ends up being enabled all of the time). A cmdline option, on the other hand, makes a tonne of sense to me, as it acts as an "opt-in" that the distribution is ready to handle the madness (because userspace will need to care about this even with the scheduler hacks proposed here). Will