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=-12.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 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 767E7C43214 for ; Fri, 6 Aug 2021 20:17:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E33C61179 for ; Fri, 6 Aug 2021 20:17:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244840AbhHFUSH (ORCPT ); Fri, 6 Aug 2021 16:18:07 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:49173 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244847AbhHFUSG (ORCPT ); Fri, 6 Aug 2021 16:18:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628281069; 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=AKEtsVz7WfVjpfJzqxqaNsm5zdfVw1TUqK/dikMgDyg=; b=OQqYZhFczGH6MYKOP8lN3nl3oacMiUftAEXLuro3l4wA0olmI5letaJw9qhkJJjVjUMby4 RHHF8qwq2uFZLtmp1puQb/zR+hwt2j0yHAfmYZHD1ppk5PdruJLxOXu4S0ipczUENDLsQ/ DeoMBhbaBGz3FCc5QQxtpZKCAetTu70= Received: from mail-oi1-f198.google.com (mail-oi1-f198.google.com [209.85.167.198]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-310-gw8WJ027NEecfzruw_vgcA-1; Fri, 06 Aug 2021 16:17:48 -0400 X-MC-Unique: gw8WJ027NEecfzruw_vgcA-1 Received: by mail-oi1-f198.google.com with SMTP id v128-20020aca61860000b029025c02a6228cso4694726oib.21 for ; Fri, 06 Aug 2021 13:17:47 -0700 (PDT) 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:in-reply-to :references:mime-version:content-transfer-encoding; bh=AKEtsVz7WfVjpfJzqxqaNsm5zdfVw1TUqK/dikMgDyg=; b=OkRA1mQP4BODsgG3ANqV19SHE+OHkMNT9h0Cui9NBR5Zutbat8QaDcQ2cYSJk3XH5U 2v8qOgvmHumgoToace0zeA8NPMqTw2rOrRQeP6HIcALcACRbYhHWNDi1SimSl9mt3T7/ VURCdBB1yTr3WlMX11LD6hU99uxrQRpEZEL7wJwi8vu8PPUzn2BDvXIXqpHwqu/OFDBG HKTJeuwyXcAYVbzRIfB16emk1p1PT60vf7W4A5D9twpwGzcj4ab3jP0n8WkfmsE6Ehj9 yCOrrR9a6CDNUPlShgF3N6BaDYqcxLQwLZuargfdQirmqpFX5Yj2ApICM1j5RB7ojDpa R0kg== X-Gm-Message-State: AOAM531FpIpo3os9ooOMj193FfO+QQDR7g/PYMloseS1anUycjEKZXeg 9p2lU8inPjpP4vjAdm3/FepzIJRuH2JRVCTYKQJ/u+YNYZensUryNu3aVfFvYxjEptpxaqelwwC xIhPaSnVX3z7Ij4ENHLajDerT X-Received: by 2002:a05:6808:b3c:: with SMTP id t28mr8529925oij.138.1628281067382; Fri, 06 Aug 2021 13:17:47 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwE/+radWlM0jhMSuigAQ6bd02/LEk6hSW+AqhKdTvsnB5GbjLi4CMMD+utdEDRsQXhnxTuVg== X-Received: by 2002:a05:6808:b3c:: with SMTP id t28mr8529912oij.138.1628281067157; Fri, 06 Aug 2021 13:17:47 -0700 (PDT) Received: from redhat.com ([198.99.80.109]) by smtp.gmail.com with ESMTPSA id 7sm164527oth.69.2021.08.06.13.17.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Aug 2021 13:17:46 -0700 (PDT) Date: Fri, 6 Aug 2021 14:17:45 -0600 From: Alex Williamson To: Jason Gunthorpe Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, peterx@redhat.com Subject: Re: [PATCH 3/7] vfio/pci: Use vfio_device_unmap_mapping_range() Message-ID: <20210806141745.1d8c3e0a.alex.williamson@redhat.com> In-Reply-To: <20210806010418.GF1672295@nvidia.com> References: <162818167535.1511194.6614962507750594786.stgit@omen> <162818325518.1511194.1243290800645603609.stgit@omen> <20210806010418.GF1672295@nvidia.com> X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 5 Aug 2021 22:04:18 -0300 Jason Gunthorpe wrote: > On Thu, Aug 05, 2021 at 11:07:35AM -0600, Alex Williamson wrote: > > @@ -2281,15 +2143,13 @@ static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data) > > > > vdev = container_of(device, struct vfio_pci_device, vdev); > > > > - /* > > - * Locking multiple devices is prone to deadlock, runaway and > > - * unwind if we hit contention. > > - */ > > - if (!vfio_pci_zap_and_vma_lock(vdev, true)) { > > + if (!down_write_trylock(&vdev->memory_lock)) { > > vfio_device_put(device); > > return -EBUSY; > > } > > Now that this is simplified so much, I wonder if we can drop the > memory_lock and just use the dev_set->lock? > > That avoids the whole down_write_trylock thing and makes it much more > understandable? Hmm, that would make this case a lot easier, but using a mutex, potentially shared across multiple devices, taken on every non-mmap read/write doesn't really feel like a good trade-off when we're currently using a per device rwsem to retain concurrency here. Thanks, Alex