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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 3C549C61DF4 for ; Fri, 24 Nov 2023 05:00:08 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=ellerman.id.au header.i=@ellerman.id.au header.a=rsa-sha256 header.s=201909 header.b=WAGvIPhM; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Sc2pt64l1z3dX3 for ; Fri, 24 Nov 2023 16:00:06 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=ellerman.id.au header.i=@ellerman.id.au header.a=rsa-sha256 header.s=201909 header.b=WAGvIPhM; dkim-atps=neutral Received: from gandalf.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Sc2nv0rtRz3d8t for ; Fri, 24 Nov 2023 15:59:15 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ellerman.id.au; s=201909; t=1700801948; bh=Q66wB5MhB4iivYOyhALqGoUT149l1Gvu6/eaYQnHlSU=; h=From:To:Subject:In-Reply-To:References:Date:From; b=WAGvIPhM5KHw/Bu+66EgTYeIOb72WnDf8q5Z+qppDZPZWtA0NB6zV2MHfn921zvD+ dJj02ihaofXO1F5uZBBk9IAXwzfMF4ykPe/OoEgvbLdrX4JShOZlx+3M+/EA1gifJT jeXj7y/VS/bXI0b+WsMD2Il+5QHTGTrhZOCgDiy1inPl7kD5EtrnxJU8ajPie1FV2M i2o0rfMALSxshqeVUxoK/uHpabXV1zGBbFtmxrKaB8VC1BYY8tZZnja5029ldBeosP 2G132zy+DQp8tVjI4kciCqwRSGA/EnYNeMRRk4MsOsQqa3dlueC6JYbiFmATyRuNVs kL14kScDbeLSA== Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4Sc2nm1hMBz4wqN; Fri, 24 Nov 2023 15:59:07 +1100 (AEDT) From: Michael Ellerman To: Dimitri John Ledkov , linuxppc-dev@lists.ozlabs.org Subject: Re: [RFC] UBUNTU: [Config] y2038: Disable COMPAT and COMPAT_32BIT_TIME on ppc64le In-Reply-To: <20231124002042.1741578-1-dimitri.ledkov@canonical.com> References: <20231124002042.1741578-1-dimitri.ledkov@canonical.com> Date: Fri, 24 Nov 2023 15:59:04 +1100 Message-ID: <87sf4vrbl3.fsf@mail.lhotse> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Dimitri John Ledkov writes: > BugLink: https://bugs.launchpad.net/bugs/2038587 > > ppc64le is exclusively little endian and 64-bit, thus there is no need > for COMPAT_32BIT_TIME, nor COMPAT. To be pedantic, the ppc64le kernel does support running 32-bit little endian userspace in compat mode (CONFIG_COMPAT=y). It's a distro choice as to whether you support COMPAT. Notably there are two other major distros that don't support COMPAT for ppc64le, and the set of 32-bit LE software is effectively empty. > diffconfig result of these changes is: > > -ARCH_MMAP_RND_COMPAT_BITS 13 > -ARCH_WANT_COMPAT_IPC_PARSE_VERSION y > -ARCH_WANT_OLD_COMPAT_IPC y > -COMPAT_BINFMT_ELF y > -COMPAT_NETLINK_MESSAGES y > -COMPAT_OLD_SIGACTION y > -HAVE_ARCH_MMAP_RND_COMPAT_BITS y > -KVM_COMPAT y > -NETFILTER_XTABLES_COMPAT y > -SYSVIPC_COMPAT y > -VDSO32 y > COMPAT y -> n > COMPAT_32BIT_TIME y -> n > +ARCH_HAS_SYSCALL_WRAPPER y > +INTERRUPT_SANITIZE_REGISTERS y > > What confused me, if the above combination is even valid or just pure > dead code. I don't entirely understand what that diff is saying, but I'll try and answer anyway. > Is it really possible to run 32bit big-endian KVM on a 64bit > little-endian POWER? Are you referring to KVM_COMPAT being disabled? That's nothing to do with big-endian. It's just controlling whether the KVM ioctls (which qemu calls) support compat handling, ie. whether you can run a 32-bit qemu under a 64-bit kernel. It's entirely expected that when COMPAT is turned off KVM_COMPAT also gets turned off. > Or is Kconfig slightly buggy and should be fixed up to prevent > offering COMPAT options when little-endian 64bit POWER kernel is being > configured? No. Like I said at the top, the kernel does support 32-bit LE compat, eventhough it's not very widely used. cheers