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 88341C43463 for ; Fri, 18 Sep 2020 17:09:21 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 228D221534 for ; Fri, 18 Sep 2020 17:09:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 228D221534 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id CB90F87A75; Fri, 18 Sep 2020 17:09:20 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id jWO92SdHTFtH; Fri, 18 Sep 2020 17:09:20 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by whitealder.osuosl.org (Postfix) with ESMTP id 3E55B87A29; Fri, 18 Sep 2020 17:09:20 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1F912C0888; Fri, 18 Sep 2020 17:09:20 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 50A05C0051 for ; Fri, 18 Sep 2020 17:09:18 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 3CD2887A75 for ; Fri, 18 Sep 2020 17:09:18 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id bUJDI-cUGiig for ; Fri, 18 Sep 2020 17:09:15 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by whitealder.osuosl.org (Postfix) with ESMTPS id 46F7E87A29 for ; Fri, 18 Sep 2020 17:09:15 +0000 (UTC) IronPort-SDR: s9dUNjLo8DTFTvGoFiFPVr95uc03RYkDO5yC5OvZV5PcFUDFH2pxqkwJtvBY1Nja/U84IokPpP Bdo62S47pA5g== X-IronPort-AV: E=McAfee;i="6000,8403,9748"; a="157387655" X-IronPort-AV: E=Sophos;i="5.77,274,1596524400"; d="scan'208";a="157387655" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Sep 2020 10:09:06 -0700 IronPort-SDR: 36xZojZG7hFQ6U+N7qlCL+5QTKGKJmvm3ksrt5N9Dqbfkd434G1c6xHARWB1J9c7oHdayituyf 9Ut6ZjLCQYtg== X-IronPort-AV: E=Sophos;i="5.77,274,1596524400"; d="scan'208";a="307938060" Received: from jacob-builder.jf.intel.com (HELO jacob-builder) ([10.7.199.155]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Sep 2020 10:09:05 -0700 Date: Fri, 18 Sep 2020 10:11:08 -0700 From: Jacob Pan To: Joerg Roedel Subject: Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format Message-ID: <20200918101108.672c2f5a@jacob-builder> In-Reply-To: <20200918094450.GP31590@8bytes.org> 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> Organization: OTC X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Cc: "Tian, Kevin" , Jacob Pan , Raj Ashok , Jonathan Corbet , Jean-Philippe Brucker , iommu@lists.linux-foundation.org, LKML , Alex Williamson , Wu Hao , David Woodhouse , Yi Sun X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" 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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu