From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f49.google.com (mail-oi0-f49.google.com [209.85.218.49]) by kanga.kvack.org (Postfix) with ESMTP id 831736B025C for ; Fri, 8 Jan 2016 22:39:54 -0500 (EST) Received: by mail-oi0-f49.google.com with SMTP id p187so5522537oia.2 for ; Fri, 08 Jan 2016 19:39:54 -0800 (PST) Received: from mail-ob0-x244.google.com (mail-ob0-x244.google.com. [2607:f8b0:4003:c01::244]) by mx.google.com with ESMTPS id u12si48018467oie.43.2016.01.08.19.39.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 08 Jan 2016 19:39:53 -0800 (PST) Received: by mail-ob0-x244.google.com with SMTP id oj9so1501619obc.0 for ; Fri, 08 Jan 2016 19:39:53 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <3a259f1cce4a3c309c2f81df715f8c2c9bb80015.1452297867.git.tony.luck@intel.com> Date: Fri, 8 Jan 2016 22:39:53 -0500 Message-ID: Subject: Re: [PATCH v8 1/3] x86: Expand exception table to allow new handling options From: Brian Gerst Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: Tony Luck , Ingo Molnar , Borislav Petkov , Andrew Morton , Andy Lutomirski , Dan Williams , Robert , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , linux-nvdimm , X86 ML On Fri, Jan 8, 2016 at 8:52 PM, Andy Lutomirski wrote: > On Fri, Jan 8, 2016 at 12:49 PM, Tony Luck wrote: >> Huge amounts of help from Andy Lutomirski and Borislav Petkov to >> produce this. Andy provided the inspiration to add classes to the >> exception table with a clever bit-squeezing trick, Boris pointed >> out how much cleaner it would all be if we just had a new field. >> >> Linus Torvalds blessed the expansion with: >> I'd rather not be clever in order to save just a tiny amount of space >> in the exception table, which isn't really criticial for anybody. >> >> The third field is a simple integer indexing into an array of handler >> functions (I thought it couldn't be a relative pointer like the other >> fields because a module may have its ex_table loaded more than 2GB away >> from the handler function - but that may not be actually true. But the >> integer is pretty flexible, we are only really using low two bits now). >> >> We start out with three handlers: >> >> 0: Legacy - just jumps the to fixup IP >> 1: Fault - provide the trap number in %ax to the fixup code >> 2: Cleaned up legacy for the uaccess error hack > > I think I preferred the relative function pointer approach. > > Also, I think it would be nicer if the machine check code would invoke > the handler regardless of which handler (or class) is selected. Then > the handlers that don't want to handle #MC can just reject them. > > Also, can you make the handlers return bool instead of int? I'm hashing up an idea that could eliminate alot of text in the .fixup section, but it needs the integer handler method to work. We have alot of fixup code that does "mov $-EFAULT, reg; jmp xxxx". If we encode the register in the third word, the handler can be generic and no fixup code for each user access would be needed. That would recover alot of the memory used by expanding the exception table. -- Brian Gerst -- 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