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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 0477AC76186 for ; Wed, 24 Jul 2019 17:06:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D776921841 for ; Wed, 24 Jul 2019 17:06:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727935AbfGXRGP (ORCPT ); Wed, 24 Jul 2019 13:06:15 -0400 Received: from foss.arm.com ([217.140.110.172]:44042 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725882AbfGXRGP (ORCPT ); Wed, 24 Jul 2019 13:06:15 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 464CE28; Wed, 24 Jul 2019 10:06:14 -0700 (PDT) Received: from [10.1.197.57] (e110467-lin.cambridge.arm.com [10.1.197.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 769E73F71F; Wed, 24 Jul 2019 10:06:12 -0700 (PDT) Subject: Re: [PATCH] dma-direct: Force unencrypted DMA under SME for certain DMA masks To: "Lendacky, Thomas" , "Kirill A. Shutemov" Cc: "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , Christoph Hellwig , Marek Szyprowski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Lianbo Jiang References: <10b83d9ff31bca88e94da2ff34e30619eb396078.1562785123.git.thomas.lendacky@amd.com> <20190724155530.hlingpcirjcf2ljg@box> From: Robin Murphy Message-ID: Date: Wed, 24 Jul 2019 18:06:11 +0100 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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24/07/2019 17:42, Lendacky, Thomas wrote: > On 7/24/19 10:55 AM, Kirill A. Shutemov wrote: >> On Wed, Jul 10, 2019 at 07:01:19PM +0000, Lendacky, Thomas wrote: >>> @@ -351,6 +355,32 @@ bool sev_active(void) >>> } >>> EXPORT_SYMBOL(sev_active); >>> >>> +/* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */ >>> +bool force_dma_unencrypted(struct device *dev) >>> +{ >>> + /* >>> + * For SEV, all DMA must be to unencrypted addresses. >>> + */ >>> + if (sev_active()) >>> + return true; >>> + >>> + /* >>> + * For SME, all DMA must be to unencrypted addresses if the >>> + * device does not support DMA to addresses that include the >>> + * encryption mask. >>> + */ >>> + if (sme_active()) { >>> + u64 dma_enc_mask = DMA_BIT_MASK(__ffs64(sme_me_mask)); >>> + u64 dma_dev_mask = min_not_zero(dev->coherent_dma_mask, >>> + dev->bus_dma_mask); >>> + >>> + if (dma_dev_mask <= dma_enc_mask) >>> + return true; >> >> Hm. What is wrong with the dev mask being equal to enc mask? IIUC, it >> means that device mask is wide enough to cover encryption bit, doesn't it? > > Not really... it's the way DMA_BIT_MASK works vs bit numbering. Let's say > that sme_me_mask has bit 47 set. __ffs64 returns 47 and DMA_BIT_MASK(47) > will generate a mask without bit 47 set (0x7fffffffffff). So the check > will catch anything that does not support at least 48-bit DMA. Couldn't that be expressed as just: if (sme_me_mask & dma_dev_mask == sme_me_mask) ? Robin.