From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05AA0C43334 for ; Fri, 17 Jun 2022 14:52:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1382884AbiFQOwZ (ORCPT ); Fri, 17 Jun 2022 10:52:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54652 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1382593AbiFQOwX (ORCPT ); Fri, 17 Jun 2022 10:52:23 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 445ED41611 for ; Fri, 17 Jun 2022 07:52:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=G4AnqWACppeg9bBHgdGkT1GET6BfWkp9HpS86zAfg54=; b=NsP6V3fPC0mZxJhJCiW9GMp3pu TQ9/d5W4gWOpsVhUFeILg/vHYralItAh5fIHvMmabefmn3eVIjaCTF7JR6iSU8U1tJkC55N5GdSyS Gfc2VjCELKnLxmJd6I188QkdZ8zsBs9Ldqdyk42THEm2TolzYGRFhAmRBHqjOBIm3osrQ5J6FvcbG taUNClZ2d2VOubVbkA/XxJZoJTmHUihaofPmRedqkopZ6DAMzlWV3y8bvQKIapV0ituwL5Jsmxjau jVRcI26pFAEFsMRUgVToi9TSmUabKF0L5FnlASIa0VG8HF9HCvvwrn8Nlzlk8o0ieNLtA8yFYhQo5 ztMCLTUg==; Received: from dhcp-077-249-017-003.chello.nl ([77.249.17.3] helo=worktop.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1o2DKS-008iO0-TS; Fri, 17 Jun 2022 14:52:15 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 9F93E9816B5; Fri, 17 Jun 2022 16:52:06 +0200 (CEST) Date: Fri, 17 Jun 2022 16:52:06 +0200 From: Peter Zijlstra To: Stephane Eranian Cc: LKML , Eric Dumazet , jpoimboe@redhat.com, Steven Rostedt Subject: Re: [RFC] pr_warn_once() issue in x86 MSR extable code Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 17, 2022 at 02:08:52PM +0300, Stephane Eranian wrote: > Hi, > > Some changes to the way invalid MSR accesses are reported by the kernel is > causing some problems with messages printed on the console. > > We have seen several cases of ex_handler_msr() printing invalid MSR > accesses once but > the callstack multiple times causing confusion on the console. > > The last time the exception MSR code was modified (5.16) by PeterZ was: > > d52a7344bdfa x86/msr: Remove .fixup usage: > > if (!safe && wrmsr && pr_warn_once("unchecked MSR access error: ...")) > show_stack_regs(regs); > > Note that this code pattern was also present, though in a different > form, before this commit. > > The problem here is that another earlier commit (5.13): > > a358f40600b3 once: implement DO_ONCE_LITE for non-fast-path "do once" > functionality > > Modifies all the pr_*_once() calls to always return true claiming that > no caller is ever > checking the return value of the functions. > > This is why we are seeing the callstack printed without the associated > printk() msg. > > I believe that having the pr_*_once() functions return true the first > time they are called > is useful especially when extra information, such as callstack, must > be printed to help > track the origin of the problem. > > The exception handling code seems to be the only place where the > return value is checked > for pr_warn_once(). A minimal change would be to create another > version of that function > that calls DO_ONCE() instead of DO_ONCE_LITE(), e.g., pr_warn_once_return(). > > I can post a patch to that effect if we all agree on the approach. > > Thanks. How about something like this? diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index dba2197c05c3..331310c29349 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -94,16 +94,18 @@ static bool ex_handler_copy(const struct exception_table_entry *fixup, static bool ex_handler_msr(const struct exception_table_entry *fixup, struct pt_regs *regs, bool wrmsr, bool safe, int reg) { - if (!safe && wrmsr && - pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n", - (unsigned int)regs->cx, (unsigned int)regs->dx, - (unsigned int)regs->ax, regs->ip, (void *)regs->ip)) + if (__ONCE_LITE_IF(!safe && wrmsr)) { + pr_warn("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n", + (unsigned int)regs->cx, (unsigned int)regs->dx, + (unsigned int)regs->ax, regs->ip, (void *)regs->ip); show_stack_regs(regs); + } - if (!safe && !wrmsr && - pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n", - (unsigned int)regs->cx, regs->ip, (void *)regs->ip)) + if (__ONCE_LITE_IF(!safe && !wrmsr)) { + pr_warn("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n", + (unsigned int)regs->cx, regs->ip, (void *)regs->ip); show_stack_regs(regs); + } if (!wrmsr) { /* Pretend that the read succeeded and returned 0. */ diff --git a/include/linux/once_lite.h b/include/linux/once_lite.h index 861e606b820f..63c3bbcef694 100644 --- a/include/linux/once_lite.h +++ b/include/linux/once_lite.h @@ -9,15 +9,27 @@ */ #define DO_ONCE_LITE(func, ...) \ DO_ONCE_LITE_IF(true, func, ##__VA_ARGS__) -#define DO_ONCE_LITE_IF(condition, func, ...) \ + +#define __ONCE_LITE_IF(condition) \ ({ \ static bool __section(".data.once") __already_done; \ - bool __ret_do_once = !!(condition); \ + bool __ret_cond = !!(condition); \ + bool __ret_once = false; \ \ if (unlikely(__ret_do_once && !__already_done)) { \ __already_done = true; \ - func(__VA_ARGS__); \ + __ret_once = true; \ } \ + unlikely(__ret_once); \ + }) + +#define DO_ONCE_LITE_IF(condition, func, ...) \ + ({ \ + bool __ret_do_once = !!(condition); \ + \ + if (__ONCE_LITE_IF(__ret_do_once)) \ + func(__VA_ARGS__); \ + \ unlikely(__ret_do_once); \ })