Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751669Ab1FNM6q (ORCPT ); Tue, 14 Jun 2011 08:58:46 -0400 Received: from casper.infradead.org ([85.118.1.10]:45601 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751292Ab1FNM6m convert rfc822-to-8bit (ORCPT ); Tue, 14 Jun 2011 08:58:42 -0400 Subject: Re: [PATCH v4 3.0-rc2-tip 2/22] 2: uprobes: Breakground page replacement. From: Peter Zijlstra To: Srikar Dronamraju Cc: Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Masami Hiramatsu , Hugh Dickins , Christoph Hellwig , Andi Kleen , Thomas Gleixner , Jonathan Corbet , Oleg Nesterov , Andrew Morton , Jim Keniston , Roland McGrath , Ananth N Mavinakayanahalli , LKML In-Reply-To: <20110613085955.GD27130@linux.vnet.ibm.com> References: <20110607125804.28590.92092.sendpatchset@localhost6.localdomain6> <20110607125835.28590.25476.sendpatchset@localhost6.localdomain6> <1307660609.2497.1773.camel@laptop> <20110613085955.GD27130@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Tue, 14 Jun 2011 14:57:29 +0200 Message-ID: <1308056249.19856.34.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2216 Lines: 55 On Mon, 2011-06-13 at 14:29 +0530, Srikar Dronamraju wrote: > * Peter Zijlstra [2011-06-10 01:03:29]: > > > On Tue, 2011-06-07 at 18:28 +0530, Srikar Dronamraju wrote: > > > + vaddr_old = kmap_atomic(old_page, KM_USER0); > > > + vaddr_new = kmap_atomic(new_page, KM_USER1); > > > + > > > + memcpy(vaddr_new, vaddr_old, PAGE_SIZE); > > > + /* poke the new insn in, ASSUMES we don't cross page boundary */ > > > + addr = vaddr; > > > + vaddr &= ~PAGE_MASK; > > > + memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz); > > > + > > > + kunmap_atomic(vaddr_new); > > > + kunmap_atomic(vaddr_old); > > > > > > > + vaddr_new = kmap_atomic(page, KM_USER0); > > > + vaddr &= ~PAGE_MASK; > > > + memcpy(opcode, vaddr_new + vaddr, uprobe_opcode_sz); > > > + kunmap_atomic(vaddr_new); > > > > > > > > > Both sequences in resp {write,read}_opcode() assume the opcode doesn't > > cross page boundaries but don't in fact have any assertions validating > > this assumption. > > > > read_opcode and write_opcode reads/writes just one breakpoint instruction > I had the below note just above the write_opcode definition. > > /* > * NOTE: > * Expect the breakpoint instruction to be the smallest size instruction for > * the architecture. If an arch has variable length instruction and the > * breakpoint instruction is not of the smallest length instruction > * supported by that architecture then we need to modify read_opcode / > * write_opcode accordingly. This would never be a problem for archs that > * have fixed length instructions. > */ Whoever reads comments anyway? :-) > Do we have archs which have a breakpoint instruction which isnt of the > smallest instruction size for that arch. If we do have can we change the > write_opcode/read_opcode while we support that architecture? Why not put a simple WARN_ON_ONCE() in there that checks the assumption? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/