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 X-Spam-Level: X-Spam-Status: No, score=-11.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 353BFC4363A for ; Thu, 22 Oct 2020 09:24:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B7C242417D for ; Thu, 22 Oct 2020 09:24:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="qHxb0cXD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2895871AbgJVJYm (ORCPT ); Thu, 22 Oct 2020 05:24:42 -0400 Received: from mx2.suse.de ([195.135.220.15]:49764 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2508564AbgJVJYm (ORCPT ); Thu, 22 Oct 2020 05:24:42 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1603358680; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=CvoA3+uVzibS3Bv3IS1AE3ffCg+FdCpAtcx7xV/jTjQ=; b=qHxb0cXD8V947WK/zTGCy4JRPTiiPnWbfjoUGIGDV7kIGwcQV3wtHATNop4KSafd8Iyz7r dBJYSt86g9B3azGQnNR+okxaki8tQWdFxwj+3+cWV+URNQDUZ0IsvxcYdKnXDvEJFSlUs+ jbrllajztgztGwWmyQ26pACn0y2fEX0= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 8F8D1AC3C; Thu, 22 Oct 2020 09:24:40 +0000 (UTC) Subject: Re: [PATCH] x86/alternative: don't call text_poke() in lazy TLB mode To: xen-devel@lists.xenproject.org, x86@kernel.org, linux-kernel@vger.kernel.org Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Andy Lutomirski References: <20201009144225.12019-1-jgross@suse.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: <28ccccfe-b95b-5c4d-af27-5004e9f02c40@suse.com> Date: Thu, 22 Oct 2020 11:24:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20201009144225.12019-1-jgross@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09.10.20 16:42, Juergen Gross wrote: > When running in lazy TLB mode the currently active page tables might > be the ones of a previous process, e.g. when running a kernel thread. > > This can be problematic in case kernel code is being modified via > text_poke() in a kernel thread, and on another processor exit_mmap() > is active for the process which was running on the first cpu before > the kernel thread. > > As text_poke() is using a temporary address space and the former > address space (obtained via cpu_tlbstate.loaded_mm) is restored > afterwards, there is a race possible in case the cpu on which > exit_mmap() is running wants to make sure there are no stale > references to that address space on any cpu active (this e.g. is > required when running as a Xen PV guest, where this problem has been > observed and analyzed). > > In order to avoid that, drop off TLB lazy mode before switching to the > temporary address space. > > Fixes: cefa929c034eb5d ("x86/mm: Introduce temporary mm structs") > Signed-off-by: Juergen Gross Can anyone look at this, please? It is fixing a real problem which has been seen several times. Juergen > --- > arch/x86/kernel/alternative.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index cdaab30880b9..cd6be6f143e8 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -807,6 +807,15 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) > temp_mm_state_t temp_state; > > lockdep_assert_irqs_disabled(); > + > + /* > + * Make sure not to be in TLB lazy mode, as otherwise we'll end up > + * with a stale address space WITHOUT being in lazy mode after > + * restoring the previous mm. > + */ > + if (this_cpu_read(cpu_tlbstate.is_lazy)) > + leave_mm(smp_processor_id()); > + > temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); > switch_mm_irqs_off(NULL, mm, current); > >