From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265338AbTLNEVN (ORCPT ); Sat, 13 Dec 2003 23:21:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265340AbTLNEVN (ORCPT ); Sat, 13 Dec 2003 23:21:13 -0500 Received: from mail.jlokier.co.uk ([81.29.64.88]:2948 "EHLO mail.shareable.org") by vger.kernel.org with ESMTP id S265338AbTLNEVH (ORCPT ); Sat, 13 Dec 2003 23:21:07 -0500 Date: Sun, 14 Dec 2003 04:20:22 +0000 From: Jamie Lokier To: Linus Torvalds Cc: Peter Horton , linux-mips@linux-mips.org, linux-kernel@vger.kernel.org Subject: Re: Possible shared mapping bug in 2.4.23 (at least MIPS/Sparc) Message-ID: <20031214042022.GA21241@mail.shareable.org> References: <20031213114134.GA9896@skeleton-jack> <20031213222626.GA20153@mail.shareable.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds wrote: > > D-cache incoherence with unsuitably aligned multiple MAP_FIXED > > mappings is also observed on SH4, SH5, PA-RISC 1.1d. The kernel may > > have the same behaviour on those platforms: allowing a mapping that > > should not be allowed. > > Why? > > If the user asks for it, it's the users own damn fault. Nobody guarantees > cache coherency to users who require fixed addresses. I agree, the users asks for it and in rare cases it's even useful. If that's your view, then several architectures have code in arch_get_unmapped_base which tests MAP_FIXED - but that function isn't called in the MAP_FIXED case any more. The attached patch removes those branches. Trivial, but untested. (It would be nice to be able to query the kernel to learn what mapping alignment, if any, can be used to avoid aliasing problems though. Something like "SHMLBA: 16k" or "SHMLBA: none" in /proc/cpuinfo and whatever other interfaces present CPU info. On some architectures the value depends on the CPU model, determined at run time. On some architectures, there isn't a value). -- Jamie Patch: irq_idle-2.6.0-test4-01jl Summary: Remove unused MAP_FIXED branches from arch_get_unmapped_area Several architectures have code in arch_get_unmapped_base which tests MAP_FIXED - but that function isn't called in the MAP_FIXED case any more. For example, this code in arch/sparc/kernel/sys_sparc.c is quite typical: if (flags & MAP_FIXED) { /* We do not accept a shared mapping if it would violate * cache aliasing constraints. */ if ((flags & MAP_SHARED) && (addr & (SHMLBA - 1))) return -EINVAL; return addr; } The function containing that test isn't called with MAP_FIXED these days, so it's redundant and misleading. This patch removes those tests from all the arch_get_unmapped_area functions which have them. diff -urN --exclude-from=dontdiff orig-2.6.0-test11/arch/mips/kernel/syscall.c mapalign-2.6.0-test11/arch/mips/kernel/syscall.c --- orig-2.6.0-test11/arch/mips/kernel/syscall.c 2003-09-02 20:49:13.000000000 +0100 +++ mapalign-2.6.0-test11/arch/mips/kernel/syscall.c 2003-12-14 04:08:10.000000000 +0000 @@ -63,16 +63,6 @@ struct vm_area_struct * vmm; int do_color_align; - if (flags & MAP_FIXED) { - /* - * We do not accept a shared mapping if it would violate - * cache aliasing constraints. - */ - if ((flags & MAP_SHARED) && (addr & shm_align_mask)) - return -EINVAL; - return addr; - } - if (len > TASK_SIZE) return -ENOMEM; do_color_align = 0; diff -urN --exclude-from=dontdiff orig-2.6.0-test11/arch/sh/kernel/sys_sh.c mapalign-2.6.0-test11/arch/sh/kernel/sys_sh.c --- orig-2.6.0-test11/arch/sh/kernel/sys_sh.c 2003-07-08 21:55:03.000000000 +0100 +++ mapalign-2.6.0-test11/arch/sh/kernel/sys_sh.c 2003-12-14 04:07:20.000000000 +0000 @@ -54,15 +54,6 @@ { struct vm_area_struct *vma; - if (flags & MAP_FIXED) { - /* We do not accept a shared mapping if it would violate - * cache aliasing constraints. - */ - if ((flags & MAP_SHARED) && (addr & (SHMLBA - 1))) - return -EINVAL; - return addr; - } - if (len > TASK_SIZE) return -ENOMEM; if (!addr) diff -urN --exclude-from=dontdiff orig-2.6.0-test11/arch/sparc/kernel/sys_sparc.c mapalign-2.6.0-test11/arch/sparc/kernel/sys_sparc.c --- orig-2.6.0-test11/arch/sparc/kernel/sys_sparc.c 2003-08-27 22:55:57.000000000 +0100 +++ mapalign-2.6.0-test11/arch/sparc/kernel/sys_sparc.c 2003-12-14 04:06:33.000000000 +0000 @@ -40,15 +40,6 @@ { struct vm_area_struct * vmm; - if (flags & MAP_FIXED) { - /* We do not accept a shared mapping if it would violate - * cache aliasing constraints. - */ - if ((flags & MAP_SHARED) && (addr & (SHMLBA - 1))) - return -EINVAL; - return addr; - } - /* See asm-sparc/uaccess.h */ if (len > TASK_SIZE - PAGE_SIZE) return -ENOMEM; diff -urN --exclude-from=dontdiff orig-2.6.0-test11/arch/sparc64/kernel/sys_sparc.c mapalign-2.6.0-test11/arch/sparc64/kernel/sys_sparc.c --- orig-2.6.0-test11/arch/sparc64/kernel/sys_sparc.c 2003-08-27 22:55:57.000000000 +0100 +++ mapalign-2.6.0-test11/arch/sparc64/kernel/sys_sparc.c 2003-12-14 04:06:46.000000000 +0000 @@ -52,15 +52,6 @@ unsigned long start_addr; int do_color_align; - if (flags & MAP_FIXED) { - /* We do not accept a shared mapping if it would violate - * cache aliasing constraints. - */ - if ((flags & MAP_SHARED) && (addr & (SHMLBA - 1))) - return -EINVAL; - return addr; - } - if (test_thread_flag(TIF_32BIT)) task_size = 0xf0000000UL; if (len > task_size || len > -PAGE_OFFSET)