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=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 6BFAAC2D0E2 for ; Tue, 22 Sep 2020 20:22:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16E732223E for ; Tue, 22 Sep 2020 20:22:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726617AbgIVUWI (ORCPT ); Tue, 22 Sep 2020 16:22:08 -0400 Received: from mga05.intel.com ([192.55.52.43]:8645 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726448AbgIVUWI (ORCPT ); Tue, 22 Sep 2020 16:22:08 -0400 IronPort-SDR: Xj93aYAV3LMQ1eJ8O7eHnc4n3iEMVqN+NrfnivW0ucUtIrS/vZZyn5zZeXH/BpEFssEpx44wxk NX5BLjC69P/A== X-IronPort-AV: E=McAfee;i="6000,8403,9752"; a="245538604" X-IronPort-AV: E=Sophos;i="5.77,291,1596524400"; d="scan'208";a="245538604" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Sep 2020 13:22:07 -0700 IronPort-SDR: 8CxwxhWgoL4Wn/YAMFmwoR54aP+Ht5jSCTlmmo9xGJ9mHUqC7zXk1hIDa44dNUPY85rDkB/xCt jmWVuCIQi6Sw== X-IronPort-AV: E=Sophos;i="5.77,291,1596524400"; d="scan'208";a="382436019" Received: from jacob-builder.jf.intel.com (HELO jacob-builder) ([10.7.199.155]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Sep 2020 13:22:07 -0700 Date: Tue, 22 Sep 2020 13:24:12 -0700 From: Jacob Pan To: Joerg Roedel Cc: Jacob Pan , iommu@lists.linux-foundation.org, LKML , Alex Williamson , Lu Baolu , David Woodhouse , Jonathan Corbet , Jean-Philippe Brucker , Eric Auger , Yi Liu , "Tian, Kevin" , Raj Ashok , Wu Hao , Yi Sun , jacob.jun.pan@linux.intel.com Subject: Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format Message-ID: <20200922132412.614d4461@jacob-builder> In-Reply-To: <20200918101108.672c2f5a@jacob-builder> References: <1599861476-53416-1-git-send-email-jacob.jun.pan@linux.intel.com> <1599861476-53416-4-git-send-email-jacob.jun.pan@linux.intel.com> <20200918094450.GP31590@8bytes.org> <20200918101108.672c2f5a@jacob-builder> Organization: OTC X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-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 Hi Joerg, I sent out v10 with Randy's comments addressed but I didn't change this patch. Does my explanation below make sense? I am hoping to make it in v5.10 since many other pieces depend on it, your guidance is much appreciated. Jacob On Fri, 18 Sep 2020 10:11:08 -0700, Jacob Pan wrote: > Hi Joerg, > > On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel wrote: > > > On Fri, Sep 11, 2020 at 02:57:52PM -0700, Jacob Pan wrote: > > > There can be multiple vendor-specific PASID data formats used in UAPI > > > structures. This patch adds enum type with a last entry which makes > > > range checking much easier. > > > > But it also makes it much easier to screw up the numbers (which are ABI) > > by inserting a new value into the middle. I prefer defines here, or > > alternativly BUILD_BUG_ON() checks for the numbers. > > > I am not following, the purpose of IOMMU_PASID_FORMAT_LAST *is* for > preparing the future insertion of new value into the middle. > The checking against IOMMU_PASID_FORMAT_LAST is to protect ABI > compatibility by making sure that out of range format are rejected in all > versions of the ABI. > For example, in v5.10, ABI has IOMMU_PASID_FORMAT_LAST = 2, then user data > with format = 2 will be rejected. So this user app will not work or > released. > > Now say in v5.11, we add one more format in the middle and set > IOMMU_PASID_FORMAT_LAST = 3. Then user data with the new format = 2 can > be supported. > > Without the checking for IOMMU_PASID_FORMAT_LAST, at v5.10 time the user > binary may succeed and become legacy binary that we cannot break in v5.11. > This renders format = 2 unusable for v5.11. > > I thought enum makes it less susceptible to programming errors than > defines by making sure the ascending order. I might have missed your > point, could you elaborate? > > > Regards, > > > > Joerg > > > > > > > > Suggested-by: Alex Williamson > > > Reviewed-by: Eric Auger > > > Signed-off-by: Jacob Pan > > > --- > > > include/uapi/linux/iommu.h | 8 ++++++-- > > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h > > > index b42acc8fe007..7cc6ee6c41f7 100644 > > > --- a/include/uapi/linux/iommu.h > > > +++ b/include/uapi/linux/iommu.h > > > @@ -298,11 +298,16 @@ struct iommu_gpasid_bind_data_vtd { > > > IOMMU_SVA_VTD_GPASID_PCD | > > > \ IOMMU_SVA_VTD_GPASID_PWT) > > > > > > +enum iommu_pasid_data_format { > > > + IOMMU_PASID_FORMAT_INTEL_VTD = 1, > > > + IOMMU_PASID_FORMAT_LAST, > > > +}; > > > + > > > /** > > > * struct iommu_gpasid_bind_data - Information about device and guest > > > PASID binding > > > * @argsz: User filled size of this data > > > * @version: Version of this data structure > > > - * @format: PASID table entry format > > > + * @format: PASID table entry format of enum > > > iommu_pasid_data_format type > > > * @flags: Additional information on guest bind request > > > * @gpgd: Guest page directory base of the guest mm to bind > > > * @hpasid: Process address space ID used for the guest mm in > > > host IOMMU @@ -321,7 +326,6 @@ struct iommu_gpasid_bind_data { > > > __u32 argsz; > > > #define IOMMU_GPASID_BIND_VERSION_1 1 > > > __u32 version; > > > -#define IOMMU_PASID_FORMAT_INTEL_VTD 1 > > > __u32 format; > > > __u32 addr_width; > > > #define IOMMU_SVA_GPASID_VAL (1 << 0) /* guest PASID valid */ > > > -- > > > 2.7.4 > > > Thanks, > > Jacob Thanks, Jacob