From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757242AbcAYNSL (ORCPT ); Mon, 25 Jan 2016 08:18:11 -0500 Received: from e28smtp03.in.ibm.com ([125.16.236.3]:49926 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757212AbcAYNSF (ORCPT ); Mon, 25 Jan 2016 08:18:05 -0500 X-IBM-Helo: d28relay03.in.ibm.com X-IBM-MailFrom: srikar@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Mon, 25 Jan 2016 18:47:24 +0530 From: Srikar Dronamraju To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, dave.hansen@linux.intel.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, aarcange@redhat.com, n-horiguchi@ah.jp.nec.com, vbabka@suse.cz, jack@suse.cz, Oleg Nesterov Subject: Re: [PATCH] mm, gup: introduce concept of "foreign" get_user_pages() Message-ID: <20160125131723.GB17206@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20160122180219.164259F1@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20160122180219.164259F1@viggo.jf.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-TM-AS-MML: disable x-cbid: 16012513-0009-0000-0000-00000A26D55C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > One of Vlastimil's comments made me go dig back in to the uprobes > code's use of get_user_pages(). I decided to change both of them > to be "foreign" accesses. > > This also fixes the nommu breakage that Vlastimil noted last time. > > Srikar, I'd appreciate if you can have a look at the uprobes.c > modifications, especially the comment. I don't think this will > change any behavior, but I want to make sure the comment is > accurate. > > --- > > From: Dave Hansen > > For protection keys, we need to understand whether protections > should be enforced in software or not. In general, we enforce > protections when working on our own task, but not when on others. > We call these "current" and "foreign" operations. > > This patch introduces a new get_user_pages() variant: > > get_user_pages_foreign() > > We modify the vanilla get_user_pages() so it can no longer be > used on mm/tasks other than 'current/current->mm', which is by > far the most common way it is called. Using it makes a few of > the call sites look a bit nicer. > > In other words, get_user_pages_foreign() is a replacement for > when get_user_pages() is called on non-current tsk/mm. > > This also switches get_user_pages_(un)locked() over to be like > get_user_pages() and not take a tsk/mm. There is no > get_user_pages_foreign_(un)locked(). If someone wants that > behavior they just have to use "__" variant and pass in > FOLL_FOREIGN explicitly. > > The uprobes is_trap_at_addr() location holds mmap_sem and > calls get_user_pages(current->mm) on an instruction address. This > makes it a pretty unique gup caller. Being an instruction access > and also really originating from the kernel (vs. the app), I opted > to consider this a 'foreign' access where protection keys will not > be enforced. > Changes for uprobes.c looks good to me. Acked-by: Srikar Dronamraju > Signed-off-by: Dave Hansen > Cc: Andrew Morton > Cc: Kirill A. Shutemov > Cc: Andrea Arcangeli > Cc: Naoya Horiguchi > Cc: Srikar Dronamraju > Cc: vbabka@suse.cz > Cc: jack@suse.cz > diff -puN kernel/events/uprobes.c~get_current_user_pages kernel/events/uprobes.c > --- a/kernel/events/uprobes.c~get_current_user_pages 2016-01-22 08:43:42.602473969 -0800 > +++ b/kernel/events/uprobes.c 2016-01-22 09:36:14.203845894 -0800 > @@ -299,7 +299,7 @@ int uprobe_write_opcode(struct mm_struct > > retry: > /* Read the page with vaddr into memory */ > - ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma); > + ret = get_user_pages_foreign(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma); > if (ret <= 0) > return ret; > > @@ -1700,7 +1700,13 @@ static int is_trap_at_addr(struct mm_str > if (likely(result == 0)) > goto out; > > - result = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL); > + /* > + * The NULL 'tsk' here ensures that any faults that occur here > + * will not be accounted to the task. 'mm' *is* current->mm, > + * but we treat this as a 'foreign' access since it is > + * essentially a kernel access to the memory. > + */ > + result = get_user_pages_foreign(NULL, mm, vaddr, 1, 0, 1, &page, NULL); > if (result < 0) > return result; > -- Thanks and Regards Srikar Dronamraju