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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 899BBC54FD0 for ; Mon, 20 Apr 2020 11:55:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 67DCF214AF for ; Mon, 20 Apr 2020 11:55:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="CZBJhyvq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726889AbgDTLzM (ORCPT ); Mon, 20 Apr 2020 07:55:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726893AbgDTLzI (ORCPT ); Mon, 20 Apr 2020 07:55:08 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1967C061A0C; Mon, 20 Apr 2020 04:55:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=u/v02NGC1oFgel1iBcflEpVS3DgIiIJMM0PTdku3nhQ=; b=CZBJhyvq0qUv3KTenjC17+groE HnljLoftFJKoNw5UOVlCYJYof/UFLtQmL5/bX9LjqyUMTo4QRE86om9NvcRONyDDMnOGVceoX+gxR 7skTn5ckWCZHYOoqhWpc3hd4V0HDNyIsFAeYa6bSvpq+bEiu36bK96SxuGk8hfmwqr6BmJyvF1Agl HpKhYqUL4S0RwC/jfr0C4LVaGSMhF+rV//Dtv4Y+Z4h74jcigb+DMo9NGcvEiyfLss4bI4oEpwBN3 Xpok6CGILMN9GEeWX+JNL2XSTrGhDYNJ1ex2JKAcJsF3nBgda4YwkG6sQ2olGScYX1ORh8O6xszEf Esp1wo2w==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jQV0y-0006P9-DC; Mon, 20 Apr 2020 11:55:04 +0000 Date: Mon, 20 Apr 2020 04:55:04 -0700 From: Christoph Hellwig To: Christian =?iso-8859-1?Q?K=F6nig?= Cc: Christoph Hellwig , Jean-Philippe Brucker , iommu@lists.linux-foundation.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, joro@8bytes.org, catalin.marinas@arm.com, will@kernel.org, robin.murphy@arm.com, kevin.tian@intel.com, baolu.lu@linux.intel.com, Jonathan.Cameron@huawei.com, jacob.jun.pan@linux.intel.com, zhangfei.gao@linaro.org, jgg@ziepe.ca, xuzaibo@huawei.com Subject: Re: [PATCH v5 02/25] iommu/sva: Manage process address spaces Message-ID: <20200420115504.GA20664@infradead.org> References: <20200414170252.714402-1-jean-philippe@linaro.org> <20200414170252.714402-3-jean-philippe@linaro.org> <20200416072852.GA32000@infradead.org> <20200416085402.GB1286150@myrica> <20200416121331.GA18661@infradead.org> <20200420074213.GA3180232@myrica> <20200420081034.GA17305@infradead.org> <6b195512-fa73-9a49-03d8-1ed92e86f607@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6b195512-fa73-9a49-03d8-1ed92e86f607@amd.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Mon, Apr 20, 2020 at 01:44:56PM +0200, Christian König wrote: > Am 20.04.20 um 10:10 schrieb Christoph Hellwig: > > On Mon, Apr 20, 2020 at 09:42:13AM +0200, Jean-Philippe Brucker wrote: > > > Right, I can see the appeal. I still like having a single mmu notifier per > > > mm because it ensures we allocate a single PASID per mm (as required by > > > x86). I suppose one alternative is to maintain a hashtable of mm->pasid, > > > to avoid iterating over all bonds during allocation. > > Given that the PASID is a pretty generic and important concept can > > we just add it directly to the mm_struct and allocate it lazily once > > we first need it? > > Well the problem is that the PASID might as well be device specific. E.g. > some devices use 16bit PASIDs, some 15bit, some other only 12bit. > > So what could (at least in theory) happen is that you need to allocate > different PASIDs for the same process because different devices need one. This directly contradicts the statement from Jean-Philippe above that x86 requires a single PASID per mm_struct. If we may need different PASIDs for different devices and can actually support this just allocating one per [device, mm_struct] would make most sense of me, as it doesn't couple otherwise disjoint state.