Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753543AbbF2Tqn (ORCPT ); Mon, 29 Jun 2015 15:46:43 -0400 Received: from mail-vn0-f52.google.com ([209.85.216.52]:44817 "EHLO mail-vn0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752461AbbF2Tqe (ORCPT ); Mon, 29 Jun 2015 15:46:34 -0400 MIME-Version: 1.0 In-Reply-To: References: Date: Mon, 29 Jun 2015 21:46:33 +0200 Message-ID: Subject: Re: [PATCH v4 00/17] x86: Rewrite exit-to-userspace code From: Richard Weinberger To: Andy Lutomirski Cc: "x86@kernel.org" , LKML , =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= , Rik van Riel , Oleg Nesterov , Denys Vlasenko , Borislav Petkov , Kees Cook , Brian Gerst , Paul McKenney Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4211 Lines: 89 Andy, On Mon, Jun 29, 2015 at 9:33 PM, Andy Lutomirski wrote: > This is the first big batch of x86 asm-to-C conversion patches. > > The exit-to-usermode code is copied in several places and is written > in a nasty combination of asm and C. It's not at all clear what > it's supposed to do, and the way it's structured makes it very hard > to work with. For example, it's not even clear why syscall exit > hooks are called only once per syscall right now. (It seems to be a > side effect of the way that rdi and rdx are handled in the asm loop, > and it seems reliable, but it's still pointlessly complicated.) The > existing code also makes context tracking overly complicated and > hard to understand. Finally, it's nearly impossible for anyone to > change what happens on exit to usermode, since the existing code is > so fragile. > > I tried to clean it up incrementally, but I decided it was too hard. > Instead, this series just replaces the code. It seems to work. > > Context tracking in particular works very differently now. The > low-level entry code checks that we're in CONTEXT_USER and switches > to CONTEXT_KERNEL. The exit code does the reverse. There is no > need to track what CONTEXT_XYZ state we came from, because we > already know. Similarly, SCHEDULE_USER is gone, since we can > reschedule if needed by simply calling schedule() from C code. > > The main things that are missing are that I haven't done the 32-bit > parts (anyone want to help?) and therefore I haven't deleted the old > C code. I also think this may break UML for trivial reasons. > > IRQ context tracking is still messy. One the cleanup progresses > to the point that we can enter CONTEXT_KERNEL in syscalls before > enabling interrupts, we can fully clean up IRQ context tracking. > > Once these land, I'll send some more :) > > Note: we might want to backport patches 1 and 2. > > Changes from v3: > - Add the syscall_arg_fault_32 test. > - Fix a pre-existing bad syscall arg buglet. > - Fix an asm glitch due to a bad rebase. > - Fix a CONFIG_PROVE_LOCKDEP warning. > Borislav: the end result of this series differs from the v3.91 that I > only in the removal of a single trailing tab. The badarg patch is in > a different place now, though, since we might want to backport it. > > Changes from v2: Misplaced the actual list -- sorry. > > Changes from v1: > - Fix bisection failure by squashing the 64-bit native and compat syscall > conversions together. The intermediate state didn't built, and fixing > it isn't worthwhile (the results will be harder to understand). > - Replace context_tracking_assert_state with CT_WARN_ON and ct_state. > - The last two patches are now. I incorrectly thought that we weren't > ready for them yet on 32-bit kernels, but I was wrong. > > Andy Lutomirski (16): > selftests/x86: Add a test for 32-bit fast syscall arg faults > x86/entry/64/compat: Fix bad fast syscall arg failure path > context_tracking: Add ct_state and CT_WARN_ON > notifiers: Assert that RCU is watching in notify_die > x86: Move C entry and exit code to arch/x86/entry/common.c > x86/traps: Assert that we're in CONTEXT_KERNEL in exception entries > x86/entry: Add enter_from_user_mode and use it in syscalls > x86/entry: Add new, comprehensible entry and exit hooks > x86/entry/64: Really create an error-entry-from-usermode code path > x86/entry/64: Migrate 64-bit and compat syscalls to new exit hooks > x86/asm/entry/64: Save all regs on interrupt entry > x86/asm/entry/64: Simplify irq stack pt_regs handling > x86/asm/entry/64: Migrate error and interrupt exit work to C > x86/entry: Remove exception_enter from most trap handlers > x86/entry: Remove SCHEDULE_USER and asm/context-tracking.h > x86/irq: Document how IRQ context tracking works and add an assertion > > Ingo Molnar (1): > uml: Fix do_signal() prototype Do you have a git tree for that? -- Thanks, //richard -- 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/