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 4FDE0C433EF for ; Sat, 30 Apr 2022 07:33:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1382291AbiD3Hgq (ORCPT ); Sat, 30 Apr 2022 03:36:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52524 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346476AbiD3Hgp (ORCPT ); Sat, 30 Apr 2022 03:36:45 -0400 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 71AC1CE139 for ; Sat, 30 Apr 2022 00:33:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1651304004; x=1682840004; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=R2jqEuLVanUhC0qbR2y40hAg+OH/oqq58hrMD8YsY64=; b=HGhbcXLvAyqVMMbj8+ls2Snpty1lTm1dSdlOb1OGi3cZ+jJDTKPf8RB6 rga21jw8o9jCodUhkO/atqjEtt1MCb9ixsWddaFPnJgQ1n4alU3KgULLJ N8naZ8Wj4K/eV1dMOGhEMhsSO5wvqg1c5ZkiAWKkbt69Ks4bjSlELFSFg 0fUjqpYOe3h3rqfLnPlCt+X36QS7Y6HPZZ0PKojLPMVAYTmQVWcf9FbXq m3DyfVFK8qDyLaMmtpxbeHNdpCybQEnV+OyXl/oQr8LIzgi6crQp1WXG7 3N3s3PuqpWJgrVjkfDoB9lUjPHxHkS/Pn8YsuQA8N1N48HQcOjEB7rR99 Q==; X-IronPort-AV: E=McAfee;i="6400,9594,10332"; a="266683588" X-IronPort-AV: E=Sophos;i="5.91,187,1647327600"; d="scan'208";a="266683588" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Apr 2022 00:33:24 -0700 X-IronPort-AV: E=Sophos;i="5.91,187,1647327600"; d="scan'208";a="582650317" Received: from aliu1-mobl.ccr.corp.intel.com (HELO [10.255.30.71]) ([10.255.30.71]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Apr 2022 00:33:19 -0700 Message-ID: <3ea91623-97ea-f318-70db-55f08922d7ce@linux.intel.com> Date: Sat, 30 Apr 2022 15:33:17 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit Content-Language: en-US To: Fenghua Yu , Jean-Philippe Brucker Cc: Dave Hansen , Tony Luck , Ashok Raj , Ravi V Shankar , Peter Zijlstra , robin.murphy@arm.com, Dave Hansen , x86 , linux-kernel , iommu , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Josh Poimboeuf , zhangfei.gao@linaro.org, Thomas Gleixner , will@kernel.org References: <22b659c7-e972-7a56-2bd7-8df3b4820d4e@intel.com> <8c044e49-74bb-df56-8a60-663013c0910e@intel.com> <63582490-a794-fd11-0380-44b27cc660b7@intel.com> <044595e6-e5d0-26c2-af8e-fc9d06906179@linux.intel.com> From: Baolu Lu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/4/30 06:19, Fenghua Yu wrote: > Hi, Jean and Baolu, > > On Fri, Apr 29, 2022 at 03:34:36PM +0100, Jean-Philippe Brucker wrote: >> On Fri, Apr 29, 2022 at 06:51:17AM -0700, Fenghua Yu wrote: >>> Hi, Baolu, >>> >>> On Fri, Apr 29, 2022 at 03:53:57PM +0800, Baolu Lu wrote: >>>> On 2022/4/28 16:39, Jean-Philippe Brucker wrote: >>>>>> The address space is what the OOM killer is after. That gets refcounted >>>>>> with mmget()/mmput()/mm->mm_users. The OOM killer is satiated by the >>>>>> page freeing done in __mmput()->exit_mmap(). >>>>>> >>>>>> Also, all the VMAs should be gone after exit_mmap(). So, even if >>>>>> vma->vm_file was holding a reference to a device driver, that reference >>>>>> should be gone by the time __mmdrop() is actually freeing the PASID. >>>>> >>>>> I agree with all that. The concern was about tearing down the PASID in the >>>>> IOMMU and device from the release() MMU notifier, which would happen in >>>>> exit_mmap(). But doing the teardown at or before __mmdrop() is fine. And >>>>> since the IOMMU drivers need to hold mm->mm_count anyway between bind() >>>>> and unbind(), I think Fenghua's fix works. >>>> >>>> But I didn't find mmgrab()/mmdrop() get called in both arm and intel >>>> IOMMU drivers. >>>> >>>> $ git grep mmgrab drivers/iommu/ >>>> [no output] >>>> >>>> Do we need to add these in a separated fix patch, or I missed anything >>>> here? >>> >>> On both ARM and X86, sva_bind() calls mmu_notifier_register()->mmgrab() and >>> sva_unbind() calls mmu_notifier_unregister()/mmu_notifier_put()->mmdrop(). >> >> Yes, although for Arm I realized the mmu_notifier grab wasn't sufficient >> so I sent a separate fix that should go in 5.18 as well >> https://lore.kernel.org/linux-iommu/20220426130444.300556-1-jean-philippe@linaro.org/ >> The Arm driver still touches the arch mm context after mmu_notifier_put(). >> I don't think X86 has that problem. > > I think so too. On X86, the mm is not used after mmu_notifier_unregister(). > > In case of supervisor mode SVM (i.e. svm is bound to init_mm), the code > is right too because init_mm and its PASID cannot be dropped and > mmu_notifier_register()/mmu_notifier_unregister() are not called. > > So I think no extra fix patch is needed on X86. Thanks, Fenghua and Jean. It's clear to me now. Jean, another quick question about the iommu_sva_bind_device() /** * iommu_sva_bind_device() - Bind a process address space to a device * @dev: the device * @mm: the mm to bind, caller must hold a reference to it * @drvdata: opaque data pointer to pass to bind callback This interface requires the caller to take a reference to mm. Which reference should it take, mm->mm_count or mm->mm_users? It's better to make it explicit in this comment. Best regards, baolu