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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A786CC433F5 for ; Wed, 5 Jan 2022 06:09:44 +0000 (UTC) Received: from localhost ([::1]:46012 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1n4zUV-0004YA-Ai for qemu-devel@archiver.kernel.org; Wed, 05 Jan 2022 01:09:43 -0500 Received: from eggs.gnu.org ([209.51.188.92]:59418) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n4zSi-0003o6-0q for qemu-devel@nongnu.org; Wed, 05 Jan 2022 01:07:53 -0500 Received: from mga03.intel.com ([134.134.136.65]:54371) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n4zSf-0002MY-F1 for qemu-devel@nongnu.org; Wed, 05 Jan 2022 01:07:51 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1641362869; x=1672898869; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:in-reply-to; bh=07p9MpW9zMg9Qp6lAa6OCqWxIJ+2lO0bV8d8+HqWdzA=; b=Ws/mM52/omj2Mut3ufcLB7BKQpHPmd+uSgN7vrWld/caCla0qf/tylFB fCpMHojKuJ22QseYnOtMmspct1BMqVluyMc6FmM77A8Dkv+deqgVg5Qt4 itLgt05qQReZUuHOghaqClMOXap5hZqyvru+3MY0GycgDSRypvQ/2d/VA dxzAK+FbVza/i2n6464sRBuoTHqiIMSNnkvUK4lmCT1LRSXGgdeOO5mWU 9gT9G4GVzRO+XGhawcW9NMCI58Z+HEumZmVqfv63bkvA+4D69PBYnkLXd q080V+DTPKpq3Yp60Fs0HQtnd4ZdkzTKjvxhl5inc7HSfwJOYJf4VTXT8 Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10217"; a="242334640" X-IronPort-AV: E=Sophos;i="5.88,262,1635231600"; d="scan'208";a="242334640" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jan 2022 22:07:45 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.88,262,1635231600"; d="scan'208";a="526379627" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.192.101]) by orsmga008.jf.intel.com with ESMTP; 04 Jan 2022 22:07:38 -0800 Date: Wed, 5 Jan 2022 14:07:04 +0800 From: Chao Peng To: Sean Christopherson Subject: Re: [PATCH v3 kvm/queue 03/16] mm/memfd: Introduce MEMFD_OPS Message-ID: <20220105060704.GA25009@chaop.bj.intel.com> References: <20211223123011.41044-1-chao.p.peng@linux.intel.com> <20211223123011.41044-4-chao.p.peng@linux.intel.com> <95d13ac7da32aa1530d6883777ef3279e4ad825d.camel@linux.intel.com> <20211231023853.GB7255@chaop.bj.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Received-SPF: none client-ip=134.134.136.65; envelope-from=chao.p.peng@linux.intel.com; helo=mga03.intel.com X-Spam_score_int: -46 X-Spam_score: -4.7 X-Spam_bar: ---- X-Spam_report: (-4.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.372, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Chao Peng Cc: Wanpeng Li , jun.nakajima@intel.com, kvm@vger.kernel.org, david@redhat.com, qemu-devel@nongnu.org, "J . Bruce Fields" , linux-mm@kvack.org, "H . Peter Anvin" , ak@linux.intel.com, Jonathan Corbet , Joerg Roedel , x86@kernel.org, Hugh Dickins , Robert Hoo , Ingo Molnar , Borislav Petkov , luto@kernel.org, Thomas Gleixner , Vitaly Kuznetsov , Jim Mattson , dave.hansen@intel.com, susie.li@intel.com, Jeff Layton , linux-kernel@vger.kernel.org, john.ji@intel.com, Yu Zhang , linux-fsdevel@vger.kernel.org, Paolo Bonzini , Andrew Morton , "Kirill A . Shutemov" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jan 04, 2022 at 05:38:38PM +0000, Sean Christopherson wrote: > On Fri, Dec 31, 2021, Chao Peng wrote: > > On Fri, Dec 24, 2021 at 11:53:15AM +0800, Robert Hoo wrote: > > > On Thu, 2021-12-23 at 20:29 +0800, Chao Peng wrote: > > > > From: "Kirill A. Shutemov" > > > > > > > > +static void notify_fallocate(struct inode *inode, pgoff_t start, > > > > pgoff_t end) > > > > +{ > > > > +#ifdef CONFIG_MEMFD_OPS > > > > + struct shmem_inode_info *info = SHMEM_I(inode); > > > > + const struct memfd_falloc_notifier *notifier; > > > > + void *owner; > > > > + bool ret; > > > > + > > > > + if (!info->falloc_notifier) > > > > + return; > > > > + > > > > + spin_lock(&info->lock); > > > > + notifier = info->falloc_notifier; > > > > + if (!notifier) { > > > > + spin_unlock(&info->lock); > > > > + return; > > > > + } > > > > + > > > > + owner = info->owner; > > > > + ret = notifier->get_owner(owner); > > > > + spin_unlock(&info->lock); > > > > + if (!ret) > > > > + return; > > > > + > > > > + notifier->fallocate(inode, owner, start, end); > > > > > > I see notifier->fallocate(), i.e. memfd_fallocate(), discards > > > kvm_memfd_fallocate_range()'s return value. Should it be checked? > > > > I think we can ignore it, just like how current mmu_notifier does, > > the return value of __kvm_handle_hva_range is discarded in > > kvm_mmu_notifier_invalidate_range_start(). Even when KVM side failed, > > it's not fatal, it should not block the operation in the primary MMU. > > If the return value is ignored, it'd be better to have no return value at all so > that it's clear fallocate() will continue on regardless of whether or not the > secondary MMU callback succeeds. E.g. if KVM can't handle the fallocate() for > whatever reason, then knowing that fallocate() will continue on means KVM should > mark the VM as dead so that the broken setup cannot be abused by userspace. After a close look, kvm_unmap_gfn_range() actually does not return a error code, so it's safe to not return in kvm_memfd_handle_range(). Chao