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 0C18AC433F5 for ; Thu, 10 Feb 2022 17:25:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245206AbiBJRY5 (ORCPT ); Thu, 10 Feb 2022 12:24:57 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:36868 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232479AbiBJRY4 (ORCPT ); Thu, 10 Feb 2022 12:24:56 -0500 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01990E7A for ; Thu, 10 Feb 2022 09:24:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1644513898; x=1676049898; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=eagqL1AoUzAckRlZtQNOqTR4fbpXscTSKvxL87Obws8=; b=GptyW4eaH/s+MjexdvXIec27BzLyglFeEKeMEEilXPeyCIv/cbka8myG 5sEG8m2kP25UpynmgAuYslJSt2FTsMlV65q04o/4t4faxzY8bKxyGUXZU AtmUKWOmRWvxZ9CtuEdyM5Xt3mNyz+kYqj+J56If5WQRaghXCG51NYZ3j AhlmrgbzkdHbp32XZ/CABhVpTCPWOXsTDhYGyYYNWVATxyjwLGw+HzcDD mXoSmf73+8x+9WkHZ3wqyZtJ1v61i2cc4yl8AEEzCBn1F4iJxO3oA+LZQ V1Wn22HNhIMBugBPpSc8OTPD41ahsHhtVo6bgJrL3xLfn7VAePgu5x3mo Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10254"; a="247129652" X-IronPort-AV: E=Sophos;i="5.88,359,1635231600"; d="scan'208";a="247129652" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Feb 2022 09:24:57 -0800 X-IronPort-AV: E=Sophos;i="5.88,359,1635231600"; d="scan'208";a="629764105" Received: from agluck-desk3.sc.intel.com ([172.25.222.60]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Feb 2022 09:24:57 -0800 Date: Thu, 10 Feb 2022 09:24:50 -0800 From: "Luck, Tony" To: Fenghua Yu Cc: Jacob Pan , Thomas Gleixner , Dave Hansen , Ingo Molnar , Borislav Petkov , Peter Zijlstra , Andy Lutomirski , Lu Baolu , Joerg Roedel , Josh Poimboeuf , Ashok Raj , Ravi V Shankar , iommu@lists.linux-foundation.org, x86 , linux-kernel Subject: Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit Message-ID: References: <20220207230254.3342514-1-fenghua.yu@intel.com> <20220207230254.3342514-6-fenghua.yu@intel.com> <20220209191614.5a3b42d4@jacob-builder> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 10, 2022 at 08:27:50AM -0800, Fenghua Yu wrote: > Hi, Jacob, > > On Wed, Feb 09, 2022 at 07:16:14PM -0800, Jacob Pan wrote: > > Hi Fenghua, > > > > On Mon, 7 Feb 2022 15:02:48 -0800, Fenghua Yu wrote: > > > > > @@ -1047,8 +1040,6 @@ struct iommu_sva *intel_svm_bind(struct device > > > *dev, struct mm_struct *mm, void } > > > > > > sva = intel_svm_bind_mm(iommu, dev, mm, flags); > > > - if (IS_ERR_OR_NULL(sva)) > > > - intel_svm_free_pasid(mm); > > If bind fails, the PASID has no IOMMU nor CPU context. It should be safe to > > free here. > > The PASID can not be freed even if bind fails. The PASID allocated earlier > (either in this thread or in another thread) might be populated to other > threads already and being used now. > > Without freeing the PASID on bind failure, the worst case is the PASID might > not be used in the process (and will be freed on process exit anyway). > > This all matches with the PASID life time described in the commit message. But what does this mean for the user that failed that intel_svm_bind_mm()? Here's a scenario: Process sets up to use PASID capable device #1. Everything works, so the process has mm->pasid, and the IOMMU has the tables to map virtual addresses coming from device #1 using that PASID. Now the same process asks to start using PASID capable device #2, but there is a failure at intel_svm_bind_mm(). Fenghua is right that we shouldn't free the PASID. It is in use by at least one thread of the process to access device #1. But what happens with device #2? Does the caller of intel_svm_bind() do the right thing with the IS_ERR_OR_NULL return value to let the user know that device #2 isn't accessible? -Tony