Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751762AbdITVTL (ORCPT ); Wed, 20 Sep 2017 17:19:11 -0400 Received: from mail-pf0-f177.google.com ([209.85.192.177]:50400 "EHLO mail-pf0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751465AbdITVTJ (ORCPT ); Wed, 20 Sep 2017 17:19:09 -0400 X-Google-Smtp-Source: AOwi7QCrF1DYrVsb/fuSIKIGrNZVqAGk8pfYIFc6ZXJly+gyYoR4XRbzjw5orNNYMjj3cQ7J0CY9Cg== Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (1.0) Subject: Re: [PATCH 2/2] x86/asm: Fix inline asm call constraints for clang From: Andy Lutomirski X-Mailer: iPhone Mail (14G60) In-Reply-To: <20170920210731.kbcibdmbd4b3ppfi@treble> Date: Wed, 20 Sep 2017 14:19:07 -0700 Cc: Dmitry Vyukov , "H. Peter Anvin" , "x86@kernel.org" , LKML , Ingo Molnar , Thomas Gleixner , Andy Lutomirski , Linus Torvalds , Alexander Potapenko , Matthias Kaehlcke , Arnd Bergmann , Peter Zijlstra , Andrey Ryabinin Message-Id: References: <31e96e6bcfcb47725e15a093b9c31660dfaad430.1505846562.git.jpoimboe@redhat.com> <7e39ef18-3e60-8cc9-ec4f-1cd02ade171f@zytor.com> <20170920210731.kbcibdmbd4b3ppfi@treble> To: Josh Poimboeuf Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v8KLJG1G030931 Content-Length: 1665 Lines: 39 > On Sep 20, 2017, at 2:07 PM, Josh Poimboeuf wrote: > >> On Wed, Sep 20, 2017 at 08:01:02PM +0200, Dmitry Vyukov wrote: >>> On Wed, Sep 20, 2017 at 7:46 PM, H. Peter Anvin wrote: >>>> On 09/20/17 10:38, Dmitry Vyukov wrote: >>>> >>>> I think we need just the frame itself and RSP pointing below this >>>> frame. If we don't have a frame, CALL instruction will smash whatever >>>> RSP happens to point to. Compiler doesn't have to setup RSP to point >>>> below used part of stack in leaf functions. >>>> >>> >>> In the kernel it does. Redzoning is not allowed in the kernel, because >>> interrupts or exceptions would also smash the redzone. >> >> I see... But it's the same for user-space signals, the first thing a >> signal should do is to skip the redzone. I guess interrupt handlers >> should switch to interrupt stack which avoids smashing redzone >> altogether. Do you mean nested interrupts/exceptions in interrupts? >> In my experience frames in leaf functions can have pretty large >> performance penalty. Wonder if we have we considered changing >> interrupt/exception handlers to avoid smashing redzones and disable >> leaf frames? > > Currently, on x86-64, I believe all exceptions have their own dedicated > stacks in the kernel, but IRQs still come in on the task's kernel stack. > > Andy, do you know if there's a reason why IRQs don't use a dedicated IST > stack? > Because IST is awful due to recursion issues. We immediately switch to an IRQ stack, though. If the kernel wanted a redzone, it would have to use IST for everything, which would entail a bunch of unpleasant hackery. > -- > Josh