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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 00066C43381 for ; Tue, 2 Apr 2019 02:41:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C80072084B for ; Tue, 2 Apr 2019 02:41:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728712AbfDBClZ (ORCPT ); Mon, 1 Apr 2019 22:41:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60514 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726411AbfDBClZ (ORCPT ); Mon, 1 Apr 2019 22:41:25 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 15549308339B; Tue, 2 Apr 2019 02:41:25 +0000 (UTC) Received: from xz-x1 (dhcp-14-116.nay.redhat.com [10.66.14.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AF356601A5; Tue, 2 Apr 2019 02:41:17 +0000 (UTC) Date: Tue, 2 Apr 2019 10:41:15 +0800 From: Peter Xu To: Alex Williamson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, eric.auger@redhat.com, cohuck@redhat.com Subject: Re: [PATCH] vfio/type1: Limit DMA mappings per container Message-ID: <20190402024115.GA11008@xz-x1> References: <155414977872.12780.13728555131525362206.stgit@gimli.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <155414977872.12780.13728555131525362206.stgit@gimli.home> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Tue, 02 Apr 2019 02:41:25 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 01, 2019 at 02:16:52PM -0600, Alex Williamson wrote: [...] > @@ -1081,8 +1088,14 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu, > goto out_unlock; > } > > + if (!atomic_add_unless(&iommu->dma_avail, -1, 0)) { > + ret = -ENOSPC; > + goto out_unlock; > + } > + > dma = kzalloc(sizeof(*dma), GFP_KERNEL); > if (!dma) { > + atomic_inc(&iommu->dma_avail); This should be the only special path to revert the change. Not sure whether this can be avoided by simply using atomic_read() or even READ_ONCE() (I feel like we don't need atomic ops with dma_avail because we've had the mutex but it of course it doesn't hurt...) to replace atomic_add_unless() above to check against zero then we do +1/-1 in vfio_[un]link_dma() only. But AFAICT this patch is correct. Reviewed-by: Peter Xu Thanks, -- Peter Xu