Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751664AbeABISo (ORCPT + 1 other); Tue, 2 Jan 2018 03:18:44 -0500 Received: from mx2.suse.de ([195.135.220.15]:56943 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750736AbeABISn (ORCPT ); Tue, 2 Jan 2018 03:18:43 -0500 Subject: Re: [PATCH] x86: xen: remove the use of VLAIS To: Nick Desaulniers Cc: ghackmann@google.com, mka@google.com, kees@google.com, srhines@google.com, Boris Ostrovsky , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org References: <1514138567-20491-1-git-send-email-nick.desaulniers@gmail.com> From: Juergen Gross Message-ID: Date: Tue, 2 Jan 2018 09:18:40 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <1514138567-20491-1-git-send-email-nick.desaulniers@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: de-DE Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On 24/12/17 19:02, Nick Desaulniers wrote: > Variable Length Arrays In Structs (VLAIS) is not supported by Clang, and > frowned upon by others. > > https://lkml.org/lkml/2013/9/23/500 > > Here, the VLAIS was used because the size of the bitmap returned from > xen_mc_entry() depended on possibly (based on kernel configuration) > runtime sized data. Rather than declaring args as a VLAIS then calling > sizeof on *args, we can define the variable length array (mask) to be a > pointer, and calculate the appropriate sizeof args manually. Further, we > can get rid of the #ifdef's and rely on num_possible_cpus() (thanks to a > helpful checkpatch warning from an earlier version of this patch). Using a pointer for mask seems to be wrong, as it is never initialized. Why don't you just use: DECLARE_BITMAP(mask, NR_CPUS); and drop the #ifdef, while keeping the manual length calculation? Juergen > > Signed-off-by: Nick Desaulniers > --- > arch/x86/xen/mmu_pv.c | 10 ++++------ > 1 file changed, 4 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c > index 4d62c07..966976c 100644 > --- a/arch/x86/xen/mmu_pv.c > +++ b/arch/x86/xen/mmu_pv.c > @@ -1325,20 +1325,18 @@ static void xen_flush_tlb_others(const struct cpumask *cpus, > { > struct { > struct mmuext_op op; > -#ifdef CONFIG_SMP > - DECLARE_BITMAP(mask, num_processors); > -#else > - DECLARE_BITMAP(mask, NR_CPUS); > -#endif > + unsigned long *mask; > } *args; > struct multicall_space mcs; > + const size_t mc_entry_size = sizeof(args->op) + > + sizeof(*args->mask) * BITS_TO_LONGS(num_possible_cpus()); > > trace_xen_mmu_flush_tlb_others(cpus, info->mm, info->start, info->end); > > if (cpumask_empty(cpus)) > return; /* nothing to do */ > > - mcs = xen_mc_entry(sizeof(*args)); > + mcs = xen_mc_entry(mc_entry_size); > args = mcs.args; > args->op.arg2.vcpumask = to_cpumask(args->mask); > >