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=-15.5 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 D90D7C433DB for ; Tue, 5 Jan 2021 17:11:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A603722CF7 for ; Tue, 5 Jan 2021 17:11:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729926AbhAERLk (ORCPT ); Tue, 5 Jan 2021 12:11:40 -0500 Received: from mail-wr1-f42.google.com ([209.85.221.42]:42833 "EHLO mail-wr1-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726151AbhAERLj (ORCPT ); Tue, 5 Jan 2021 12:11:39 -0500 Received: by mail-wr1-f42.google.com with SMTP id m5so36845819wrx.9; Tue, 05 Jan 2021 09:11:22 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=xJK/r8p/by9FBkOupFAoyDbfZBUjbXuGcfwcyoGTbxo=; b=bjG4+MEnVE71pJnAB0bk+/SQkyHuEWsF7kzjrfiUoqTxeFKj+/KkPs+fijCSkTLC6e gGjugJzLBtFZ96PqL0ND+hTBJyWUztgE2YbOl3NRCFBbxAcMlpJMwcdhU3oiLZ9zefKM HbNYyCWC4Lj40IPqEw5yTVU7O6IwsXyiz/pMESE9GKu75dGIVfFJ0jI7OA2A6Gf5wu6A LX51hyBhY83dusBugFVQWj4C3C97RbtZ3W7CIm2bz22hA+2q0nKt6LZ37jJ583SevBoo 8ChPaSV1wKLm5hZWDMAnYzYpv0UMjj6DNxY3X0EzyvaIFT75U1FvAWihe+bGf1LuLI9v oZDw== X-Gm-Message-State: AOAM533UV7iBKgPXMqMYgwaLPz4qA4wtHrUcyVm7mMYQj+6r7oGDQzsm PNaM8mOWcaBjJl2R7qe6fuw6b5TTTZc= X-Google-Smtp-Source: ABdhPJwwQhKHTvXqjkUoaoc28eF6ttd0kJkNKYR0quC5RSyRLD0T9CFJfhAC22jsSrmEW+R9C8mVDg== X-Received: by 2002:adf:ba0c:: with SMTP id o12mr550774wrg.322.1609866656716; Tue, 05 Jan 2021 09:10:56 -0800 (PST) Received: from liuwe-devbox-debian-v2 ([51.145.34.42]) by smtp.gmail.com with ESMTPSA id g191sm155385wmg.39.2021.01.05.09.10.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Jan 2021 09:10:56 -0800 (PST) Date: Tue, 5 Jan 2021 17:10:54 +0000 From: Wei Liu To: Michael Kelley Cc: Wei Liu , Sasha Levin , vkuznets , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "x86@kernel.org" , "hpa@zytor.com" , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "stable@kernel.org" , KY Srinivasan , Haiyang Zhang , Stephen Hemminger Subject: Re: [PATCH] x86/hyper-v: guard against cpu mask changes in hyperv_flush_tlb_others() Message-ID: <20210105171054.7s2ggrlbsod7pigo@liuwe-devbox-debian-v2> References: <20201001013814.2435935-1-sashal@kernel.org> <87o8lm9te3.fsf@vitty.brq.redhat.com> <20201001115359.6jhhrybemnhizgok@liuwe-devbox-debian-v2> <20201001130400.GE2415204@sasha-vm> <20201005145851.hdyaeqo3celt2wtr@liuwe-devbox-debian-v2> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 05, 2021 at 04:59:10PM +0000, Michael Kelley wrote: > From: Wei Liu Sent: Monday, October 5, 2020 7:59 AM > > > > On Sat, Oct 03, 2020 at 05:40:15PM +0000, Michael Kelley wrote: > > > From: Sasha Levin Sent: Thursday, October 1, 2020 6:04 AM > > > > > > > > On Thu, Oct 01, 2020 at 11:53:59AM +0000, Wei Liu wrote: > > > > >On Thu, Oct 01, 2020 at 11:40:04AM +0200, Vitaly Kuznetsov wrote: > > > > >> Sasha Levin writes: > > > > >> > > > > >> > cpumask can change underneath us, which is generally safe except when we > > > > >> > call into hv_cpu_number_to_vp_number(): if cpumask ends up empty we pass > > > > >> > num_cpu_possible() into hv_cpu_number_to_vp_number(), causing it to read > > > > >> > garbage. As reported by KASAN: > > > > >> > > > > > >> > [ 83.504763] BUG: KASAN: slab-out-of-bounds in hyperv_flush_tlb_others > > > > (include/asm-generic/mshyperv.h:128 arch/x86/hyperv/mmu.c:112) > > > > >> > [ 83.908636] Read of size 4 at addr ffff888267c01370 by task kworker/u8:2/106 > > > > >> > [ 84.196669] CPU: 0 PID: 106 Comm: kworker/u8:2 Tainted: G W 5.4.60 #1 > > > > >> > [ 84.196669] Hardware name: Microsoft Corporation Virtual Machine/Virtual > > Machine, > > > > BIOS 090008 12/07/2018 > > > > >> > [ 84.196669] Workqueue: writeback wb_workfn (flush-8:0) > > > > >> > [ 84.196669] Call Trace: > > > > >> > [ 84.196669] dump_stack (lib/dump_stack.c:120) > > > > >> > [ 84.196669] print_address_description.constprop.0 (mm/kasan/report.c:375) > > > > >> > [ 84.196669] __kasan_report.cold (mm/kasan/report.c:507) > > > > >> > [ 84.196669] kasan_report (arch/x86/include/asm/smap.h:71 > > > > mm/kasan/common.c:635) > > > > >> > [ 84.196669] hyperv_flush_tlb_others (include/asm-generic/mshyperv.h:128 > > > > arch/x86/hyperv/mmu.c:112) > > > > >> > [ 84.196669] flush_tlb_mm_range (arch/x86/include/asm/paravirt.h:68 > > > > arch/x86/mm/tlb.c:798) > > > > >> > [ 84.196669] ptep_clear_flush (arch/x86/include/asm/tlbflush.h:586 mm/pgtable- > > > > generic.c:88) > > > > >> > > > > > >> > Fixes: 0e4c88f37693 ("x86/hyper-v: Use cheaper > > > > HVCALL_FLUSH_VIRTUAL_ADDRESS_{LIST,SPACE} hypercalls when possible") > > > > >> > Cc: Vitaly Kuznetsov > > > > >> > Cc: stable@kernel.org > > > > >> > Signed-off-by: Sasha Levin > > > > >> > --- > > > > >> > arch/x86/hyperv/mmu.c | 4 +++- > > > > >> > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > >> > > > > > >> > diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c > > > > >> > index 5208ba49c89a9..b1d6afc5fc4a3 100644 > > > > >> > --- a/arch/x86/hyperv/mmu.c > > > > >> > +++ b/arch/x86/hyperv/mmu.c > > > > >> > @@ -109,7 +109,9 @@ static void hyperv_flush_tlb_others(const struct cpumask > > > > *cpus, > > > > >> > * must. We will also check all VP numbers when walking the > > > > >> > * supplied CPU set to remain correct in all cases. > > > > >> > */ > > > > >> > - if (hv_cpu_number_to_vp_number(cpumask_last(cpus)) >= 64) > > > > >> > + int last = cpumask_last(cpus); > > > > >> > + > > > > >> > + if (last < num_possible_cpus() && > > hv_cpu_number_to_vp_number(last) >= > > > > 64) > > > > >> > goto do_ex_hypercall; > > > > >> > > > > >> In case 'cpus' can end up being empty (I'm genuinely suprised it can) > > > > > > > > I was just as surprised as you and spent the good part of a day > > > > debugging this. However, a: > > > > > > > > WARN_ON(cpumask_empty(cpus)); > > > > > > > > triggers at that line of code even though we check for cpumask_empty() > > > > at the entry of the function. > > > > > > What does the call stack look like when this triggers? I'm curious about > > > the path where the 'cpus' could be changing while the flush call is in > > > progress. > > > > > > I wonder if CPUs could ever be added to the mask? Removing CPUs can > > > be handled with some care because an unnecessary flush doesn't hurt > > > anything. But adding CPUs has serious correctness problems. > > > > > > > The cpumask_empty check is done before disabling irq. Is it possible > > the mask is modified by an interrupt? > > > > If there is a reliable way to trigger this bug, we may be able to test > > the following patch. > > > > diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c > > index 5208ba49c89a..23fa08d24c1a 100644 > > --- a/arch/x86/hyperv/mmu.c > > +++ b/arch/x86/hyperv/mmu.c > > @@ -66,11 +66,13 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus, > > if (!hv_hypercall_pg) > > goto do_native; > > > > - if (cpumask_empty(cpus)) > > - return; > > - > > local_irq_save(flags); > > > > + if (cpumask_empty(cpus)) { > > + local_irq_restore(flags); > > + return; > > + } > > + > > flush_pcpu = (struct hv_tlb_flush **) > > this_cpu_ptr(hyperv_pcpu_input_arg); > > This thread died out 3 months ago without any patches being taken. > I recently hit the problem again at random, though not in a > reproducible way. > > I'd like to take Wei Liu's latest proposal to check for an empty > cpumask *after* interrupts are disabled. I think this will almost > certainly solve the problem, and in a cleaner way than Sasha's > proposal. I'd also suggest adding a comment in the code to note > the importance of the ordering. > Sure. Let me prepare a proper patch. Wei.