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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C248DC00528 for ; Thu, 3 Aug 2023 19:39:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230445AbjHCTjR (ORCPT ); Thu, 3 Aug 2023 15:39:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34686 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229777AbjHCTjO (ORCPT ); Thu, 3 Aug 2023 15:39:14 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A6643C3B for ; Thu, 3 Aug 2023 12:38:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1691091504; 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=C8fBRKG84oTUzu4cJ0upEFkniwHWsF/Sd26+sDxvy08=; b=BF+mX3/m5A2fldN7HUGVozMMj68lo8e76Y09mcEEJNRcc8RsZgWrC6WTmvfLc72zE6MeHV EDW4sbdpKA33/QCSKrZ8t2z72594fN2OjAjryJISbPWTsILkdCyWd927pk4Xa4qN7YsY3+ FMvs4PH26TxAfUjWg9WN7/U2llluc9E= Received: from mail-io1-f69.google.com (mail-io1-f69.google.com [209.85.166.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-493-v7zvVz-5Nsmi4nPLXSLGIw-1; Thu, 03 Aug 2023 15:38:21 -0400 X-MC-Unique: v7zvVz-5Nsmi4nPLXSLGIw-1 Received: by mail-io1-f69.google.com with SMTP id ca18e2360f4ac-7873f24e7edso109235239f.3 for ; Thu, 03 Aug 2023 12:38:21 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691091500; x=1691696300; h=content-transfer-encoding:mime-version:organization:references :in-reply-to:message-id:subject:cc:to:from:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=C8fBRKG84oTUzu4cJ0upEFkniwHWsF/Sd26+sDxvy08=; b=L8AkKCLq2TU3fTvrCmRLC18WREHH3rDmwmOcApaV50/jrIkmipNwHE64K+ELrioUun D1vPxgYiQcjcLNayFElMkkv78UI1P96Q5UTRFcbJiutddgbymep8YMNoq+uPROvc40C6 MMjxSItNW3yrK3ElIGnNc1Ph5c6ske8XI2wp5YnTXZrz0VQC8icWYMx8TTWkNe1fwKBp nz5SK9PGtZxY2AMCDfrwtpV3KVEuqg0bXabTPeHeWMcTvEXtiLxTEvmBA9sYwvoG4xQc M1SkD7i8ZsUA6EsTCH39+bJ0hsfSgYJAuJPgfVJo90pFOK9OxraZwkgxpuFys9U8eYhi Zmhw== X-Gm-Message-State: ABy/qLYv3iHzVp7XjFl7bs5A4COt3ozEFLJ1v6792Uc4uwVaf/4w9sYY wdG3iF8hMs6AKbXycocjVsf5j1gTrNXTDA+oUDMdyRxMgmZXsCFDiN3LVSvUtP4zsJ1zCUPRzri L4MO/9x71EYt2fu8GjZL7bY/t X-Received: by 2002:a92:d083:0:b0:349:19e:7656 with SMTP id h3-20020a92d083000000b00349019e7656mr13385730ilh.28.1691091500566; Thu, 03 Aug 2023 12:38:20 -0700 (PDT) X-Google-Smtp-Source: APBJJlFozrDPoA3AZ5UQWG5fcKBYQDbRoiwLlBgBEKUdt19LvvvypUn54PZ7JdYNXseH/zc0WqTLYA== X-Received: by 2002:a92:d083:0:b0:349:19e:7656 with SMTP id h3-20020a92d083000000b00349019e7656mr13385718ilh.28.1691091500314; Thu, 03 Aug 2023 12:38:20 -0700 (PDT) Received: from redhat.com ([38.15.60.12]) by smtp.gmail.com with ESMTPSA id t7-20020a92cc47000000b00345d6e8ded4sm176994ilq.25.2023.08.03.12.38.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Aug 2023 12:38:19 -0700 (PDT) Date: Thu, 3 Aug 2023 13:38:12 -0600 From: Alex Williamson To: Dmitry Torokhov Cc: Paolo Bonzini , Greg KH , Sean Christopherson , Roxana Bradescu , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/2] kvm/vfio: ensure kvg instance stays around in kvm_vfio_group_add() Message-ID: <20230803133812.491956b9.alex.williamson@redhat.com> In-Reply-To: <20230714224538.404793-1-dmitry.torokhov@gmail.com> References: <20230714224538.404793-1-dmitry.torokhov@gmail.com> Organization: Red Hat 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 Fri, 14 Jul 2023 15:45:32 -0700 Dmitry Torokhov wrote: > kvm_vfio_group_add() creates kvg instance, links it to kv->group_list, > and calls kvm_vfio_file_set_kvm() with kvg->file as an argument after > dropping kv->lock. If we race group addition and deletion calls, kvg > instance may get freed by the time we get around to calling > kvm_vfio_file_set_kvm(). > > Previous iterations of the code did not reference kvg->file outside of > the critical section, but used a temporary variable. Still, they had > similar problem of the file reference being owned by kvg structure and > potential for kvm_vfio_group_del() dropping it before > kvm_vfio_group_add() had a chance to complete. > > Fix this by moving call to kvm_vfio_file_set_kvm() under the protection > of kv->lock. We already call it while holding the same lock when vfio > group is being deleted, so it should be safe here as well. > > Fixes: 2fc1bec15883 ("kvm: set/clear kvm to/from vfio_group when group add/delete") > Reviewed-by: Alex Williamson > Signed-off-by: Dmitry Torokhov > --- Applied series to vfio next branch for v6.6. There's a minor rebase involved, so please double check the results: https://github.com/awilliam/linux-vfio/commits/next Thanks, Alex > > v3: added Alex's reviewed-by > > v2: updated commit description with the correct "Fixes" tag (per Alex), > expanded commit description to mention issues with the earlier > implementation of kvm_vfio_group_add(). > > virt/kvm/vfio.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c > index 9584eb57e0ed..cd46d7ef98d6 100644 > --- a/virt/kvm/vfio.c > +++ b/virt/kvm/vfio.c > @@ -179,10 +179,10 @@ static int kvm_vfio_group_add(struct kvm_device *dev, unsigned int fd) > list_add_tail(&kvg->node, &kv->group_list); > > kvm_arch_start_assignment(dev->kvm); > + kvm_vfio_file_set_kvm(kvg->file, dev->kvm); > > mutex_unlock(&kv->lock); > > - kvm_vfio_file_set_kvm(kvg->file, dev->kvm); > kvm_vfio_update_coherency(dev); > > return 0;