Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752137AbdF3PpF convert rfc822-to-8bit (ORCPT ); Fri, 30 Jun 2017 11:45:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:58188 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751072AbdF3PpD (ORCPT ); Fri, 30 Jun 2017 11:45:03 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5A91C22BE6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org MIME-Version: 1.0 In-Reply-To: <20170630131148.yszdjakekrwqlf6k@treble> References: <20170629175333.bicpvbwo4d5pdbak@treble> <20170629190559.ttw52ahwtsjynayx@treble> <20170629214134.c36krjhvzegwkfjk@treble> <20170630021249.cqkszxaqtwakmzpg@treble> <20170630131148.yszdjakekrwqlf6k@treble> From: Andy Lutomirski Date: Fri, 30 Jun 2017 08:44:40 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 6/8] x86/entry: add unwind hint annotations To: Josh Poimboeuf Cc: Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , live-patching@vger.kernel.org, Linus Torvalds , Jiri Slaby , Ingo Molnar , "H. Peter Anvin" , Peter Zijlstra , Mike Galbraith Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2260 Lines: 63 On Fri, Jun 30, 2017 at 6:11 AM, Josh Poimboeuf wrote: > On Thu, Jun 29, 2017 at 10:41:44PM -0700, Andy Lutomirski wrote: >> On Thu, Jun 29, 2017 at 10:05 PM, Andy Lutomirski wrote: >> > Hmm. There's another option that might be considerably nicer, though: >> > put the IRQ stack at a known (at link time) position *in percpu >> > space*. (Presumably it already is -- I haven't checked.) Then we do: >> > >> > .macro ENTER_IRQ_STACK old_rsp >> > DEBUG_ENTRY_ASSERT_IRQS_OFF >> > movq %rsp, \old_rsp >> > incl PER_CPU_VAR(irq_count) >> > >> > /* >> > * Right now, if we just incremented irq_count to zero, we've >> > * claimed the IRQ stack but we haven't switched to it yet. >> > * Anything that can interrupt us here without using IST >> > * must be *extremely* careful to limit its stack usage. >> > */ >> > jnz .Lpush_old_rsp_\@ >> > movq \old_rsp, PER_CPU_VAR(top_word_in_irq_stack) >> > movq PER_CPU_VAR(irq_stack_ptr), %rsp >> > .Lpush_old_rsp_\@: >> > pushq \old_rsp >> > .endm >> > >> >> How about the two commits here (well, soon to be there once gitweb catches up): >> >> https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_irq_stack&id=0f56a55bb133cd53ccb78ca51378086296618322 >> >> If you like them, want to add them to your series? > > The second patch looks good to me, thanks. I can pick up the patches. > > A few comments about the first patch: > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_irq_stack&id=3e2aa2102cc1c5e60d4a8637bff78d0478a55059 > > - It uses a '693:' label instead of '.Lirqs_off_\@:' Touché! > > - There's a comment I don't follow: > > "Anything that can interrupt us here without using IST must be > *extremely* careful to limit its stack usage." > > What specifically could interrupt there without using IST? #DB, later on in the series. I'll update the comment. > > - Since do_softirq_own_stack() is a callable function, I think it still > needs to save rbp. Whoops. > > - Why change the "jmp error_exit" to "ret" in > xen_do_hypervisor_callback()? To match the other change I made there. I removed both.