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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 881C7C3A5A2 for ; Tue, 3 Sep 2019 22:15:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 568EF21883 for ; Tue, 3 Sep 2019 22:15:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=shipmail.org header.i=@shipmail.org header.b="gzAlelyj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726441AbfICWPe (ORCPT ); Tue, 3 Sep 2019 18:15:34 -0400 Received: from ste-pvt-msa1.bahnhof.se ([213.80.101.70]:12727 "EHLO ste-pvt-msa1.bahnhof.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725977AbfICWPe (ORCPT ); Tue, 3 Sep 2019 18:15:34 -0400 Received: from localhost (localhost [127.0.0.1]) by ste-pvt-msa1.bahnhof.se (Postfix) with ESMTP id AAA2C3F671; Wed, 4 Sep 2019 00:15:31 +0200 (CEST) Authentication-Results: ste-pvt-msa1.bahnhof.se; dkim=pass (1024-bit key; unprotected) header.d=shipmail.org header.i=@shipmail.org header.b=gzAlelyj; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at bahnhof.se Received: from ste-pvt-msa1.bahnhof.se ([127.0.0.1]) by localhost (ste-pvt-msa1.bahnhof.se [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Mux16M2QUtvF; Wed, 4 Sep 2019 00:15:30 +0200 (CEST) Received: from mail1.shipmail.org (h-205-35.A357.priv.bahnhof.se [155.4.205.35]) (Authenticated sender: mb878879) by ste-pvt-msa1.bahnhof.se (Postfix) with ESMTPA id 41A923F40A; Wed, 4 Sep 2019 00:15:27 +0200 (CEST) Received: from localhost.localdomain (h-205-35.A357.priv.bahnhof.se [155.4.205.35]) by mail1.shipmail.org (Postfix) with ESMTPSA id A05D8360160; Wed, 4 Sep 2019 00:15:26 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=shipmail.org; s=mail; t=1567548926; bh=nIA64ocI+n5D4OB+HLLwxnXOxaEz/oh4I3ffyVh/4nI=; h=Subject:From:To:Cc:References:Date:In-Reply-To:From; b=gzAlelyj5XfF8b0pUv5ucT29pTfUWzHP+CHn+fdiPmCWMNfcMMYM/NgEKnnzNigLa rXY9n015AJAntQ8+AkhcwiR3QzM+/D4MknyfY0yLeZU4v8NM8DZwIDYXOa5Dx3p3RL 7/OtoeIHgTVIiPT7kVVZla9sAEl+lsHl9M83Z7vc= Subject: Re: [PATCH v2 3/4] drm/ttm, drm/vmwgfx: Correctly support support AMD memory encryption From: =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28VMware=29?= To: Andy Lutomirski Cc: Dave Hansen , Daniel Vetter , dri-devel , pv-drivers@vmware.com, VMware Graphics , Linux Kernel Mailing List , Tom Lendacky , Thomas Hellstrom , Peter Zijlstra , Dave Hansen , Heiko Carstens , Christian Borntraeger , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Thomas Gleixner , =?UTF-8?Q?Christian_K=c3=b6nig?= References: <20190903131504.18935-1-thomas_os@shipmail.org> <20190903131504.18935-4-thomas_os@shipmail.org> <6d0fafcc-b596-481b-7b22-1f26f0c02c5c@intel.com> <7fa3b178-b9b4-2df9-1eee-54e24d48342e@intel.com> <44b094c8-63fe-d9e5-1bf4-7da0788caccf@shipmail.org> Organization: VMware Inc. Message-ID: <6d122d62-9c96-4c29-8d06-02f7134e5e2a@shipmail.org> Date: Wed, 4 Sep 2019 00:15:26 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <44b094c8-63fe-d9e5-1bf4-7da0788caccf@shipmail.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/4/19 12:08 AM, Thomas Hellström (VMware) wrote: > On 9/3/19 11:46 PM, Andy Lutomirski wrote: >> On Tue, Sep 3, 2019 at 2:05 PM Thomas Hellström (VMware) >> wrote: >>> On 9/3/19 10:51 PM, Dave Hansen wrote: >>>> On 9/3/19 1:36 PM, Thomas Hellström (VMware) wrote: >>>>> So the question here should really be, can we determine already at >>>>> mmap >>>>> time whether backing memory will be unencrypted and adjust the *real* >>>>> vma->vm_page_prot under the mmap_sem? >>>>> >>>>> Possibly, but that requires populating the buffer with memory at mmap >>>>> time rather than at first fault time. >>>> I'm not connecting the dots. >>>> >>>> vma->vm_page_prot is used to create a VMA's PTEs regardless of if they >>>> are created at mmap() or fault time.  If we establish a good >>>> vma->vm_page_prot, can't we just use it forever for demand faults? >>> With SEV I think that we could possibly establish the encryption flags >>> at vma creation time. But thinking of it, it would actually break with >>> SME where buffer content can be moved between encrypted system memory >>> and unencrypted graphics card PCI memory behind user-space's back. That >>> would imply killing all user-space encrypted PTEs and at fault time set >>> up new ones pointing to unencrypted PCI memory.. >>> >>>> Or, are you concerned that if an attempt is made to demand-fault page >>>> that's incompatible with vma->vm_page_prot that we have to SEGV? >>>> >>>>> And it still requires knowledge whether the device DMA is always >>>>> unencrypted (or if SEV is active). >>>> I may be getting mixed up on MKTME (the Intel memory encryption) and >>>> SEV.  Is SEV supported on all memory types?  Page cache, hugetlbfs, >>>> anonymous?  Or just anonymous? >>> SEV AFAIK encrypts *all* memory except DMA memory. To do that it uses a >>> SWIOTLB backed by unencrypted memory, and it also flips coherent DMA >>> memory to unencrypted (which is a very slow operation and patch 4 deals >>> with caching such memory). >>> >> I'm still lost.  You have some fancy VMA where the backing pages >> change behind the application's back.  This isn't particularly novel >> -- plain old anonymous memory and plain old mapped files do this too. >> Can't you all the insert_pfn APIs and call it a day?  What's so >> special that you need all this magic?  ISTM you should be able to >> allocate memory that's addressable by the device (dma_alloc_coherent() >> or whatever) and then map it into user memory just like you'd map any >> other page. >> >> I feel like I'm missing something here. > > Yes, so in this case we use dma_alloc_coherent(). > > With SEV, that gives us unencrypted pages. (Pages whose linear kernel > map is marked unencrypted). With SME that (typcially) gives us > encrypted pages. In both these cases, vm_get_page_prot() returns > an encrypted page protection, which lands in vma->vm_page_prot. > > In the SEV case, we therefore need to modify the page protection to > unencrypted. Hence we need to know whether we're running under SEV and > therefore need to modify the protection. If not, the user-space PTE > would incorrectly have the encryption flag set. > > /Thomas > > And, of course, had we not been "fancy", we could have used dma_mmap_coherent(), which in theory should set up the correct user-space page protection. But now we're moving stuff around so we can't. /Thomas