From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f71.google.com (mail-pg0-f71.google.com [74.125.83.71]) by kanga.kvack.org (Postfix) with ESMTP id E3F6E6B0260 for ; Wed, 18 Jan 2017 06:36:47 -0500 (EST) Received: by mail-pg0-f71.google.com with SMTP id d185so13327681pgc.2 for ; Wed, 18 Jan 2017 03:36:47 -0800 (PST) Received: from EUR01-HE1-obe.outbound.protection.outlook.com (mail-he1eur01on0127.outbound.protection.outlook.com. [104.47.0.127]) by mx.google.com with ESMTPS id v4si7733792pgo.267.2017.01.18.03.36.46 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 18 Jan 2017 03:36:46 -0800 (PST) Subject: Re: [PATCHv2 3/5] x86/mm: fix native mmap() in compat bins and vice-versa References: <20170116123310.22697-1-dsafonov@virtuozzo.com> <20170116123310.22697-4-dsafonov@virtuozzo.com> From: Dmitry Safonov Message-ID: <72d16541-17c3-acb6-1d0d-2d6cf0565f35@virtuozzo.com> Date: Wed, 18 Jan 2017 14:33:26 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: "linux-kernel@vger.kernel.org" , Dmitry Safonov <0x7f454c46@gmail.com>, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , X86 ML , "linux-mm@kvack.org" On 01/17/2017 11:29 PM, Andy Lutomirski wrote: > On Mon, Jan 16, 2017 at 4:33 AM, Dmitry Safonov wrote: >> Fix 32-bit compat_sys_mmap() mapping VMA over 4Gb in 64-bit binaries >> and 64-bit sys_mmap() mapping VMA only under 4Gb in 32-bit binaries. >> Changed arch_get_unmapped_area{,_topdown}() to recompute mmap_base >> for those cases and use according high/low limits for vm_unmapped_area() >> The recomputing of mmap_base may make compat sys_mmap() in 64-bit >> binaries a little slower than native, which uses already known from exec >> time mmap_base - but, as it returned buggy address, that case seemed >> unused previously, so no performance degradation for already used ABI. > > This looks plausibly correct but rather weird -- why does this code > need to distinguish between all four cases (pure 32-bit, pure 64-bit, > 64-bit mmap layout doing 32-bit call, 32-bit layout doing 64-bit > call)? Only by need to know is mm->mmap_base computed initialy for 32-bit or for 64-bit. > >> Can be optimized in future by introducing mmap_compat_{,legacy}_base >> in mm_struct. > > Hmm. Would it make sense to do it this way from the beginning? That would, but mm_struct is in generic code, if adding those new bases is fine, than I'll do that in v3. It will look somehow like: : if (in_compat_syscall()) : return current->mm->mmap_compat_base; : else : return current->mm->mmap_base; > > If adding an in_32bit_syscall() helper would help, then by all means > please do so. > > --Andy > -- Dmitry -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org