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=-2.2 required=3.0 tests=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 AB55DC2BB55 for ; Wed, 15 Apr 2020 16:05:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 90FA221734 for ; Wed, 15 Apr 2020 16:05:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2410199AbgDOQFy (ORCPT ); Wed, 15 Apr 2020 12:05:54 -0400 Received: from foss.arm.com ([217.140.110.172]:47960 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2410192AbgDOQFu (ORCPT ); Wed, 15 Apr 2020 12:05:50 -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 B41691FB; Wed, 15 Apr 2020 09:05:49 -0700 (PDT) Received: from [192.168.2.22] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 894FB3F6C4; Wed, 15 Apr 2020 09:05:48 -0700 (PDT) Subject: Re: [PATCH kvmtool v3] Add emulation for CFI compatible flash memory To: Ard Biesheuvel , Alexandru Elisei , sami.mujawar@arm.com Cc: Will Deacon , Julien Thierry , kvm@vger.kernel.org, Raphael Gault , Linux ARM , kvmarm References: <20200221165532.90618-1-andre.przywara@arm.com> <2d3bad43-10a5-3ee1-72e7-e1da1d6c65dd@arm.com> From: =?UTF-8?Q?Andr=c3=a9_Przywara?= Autocrypt: addr=andre.przywara@arm.com; prefer-encrypt=mutual; keydata= xsFNBFNPCKMBEAC+6GVcuP9ri8r+gg2fHZDedOmFRZPtcrMMF2Cx6KrTUT0YEISsqPoJTKld tPfEG0KnRL9CWvftyHseWTnU2Gi7hKNwhRkC0oBL5Er2hhNpoi8x4VcsxQ6bHG5/dA7ctvL6 kYvKAZw4X2Y3GTbAZIOLf+leNPiF9175S8pvqMPi0qu67RWZD5H/uT/TfLpvmmOlRzNiXMBm kGvewkBpL3R2clHquv7pB6KLoY3uvjFhZfEedqSqTwBVu/JVZZO7tvYCJPfyY5JG9+BjPmr+ REe2gS6w/4DJ4D8oMWKoY3r6ZpHx3YS2hWZFUYiCYovPxfj5+bOr78sg3JleEd0OB0yYtzTT esiNlQpCo0oOevwHR+jUiaZevM4xCyt23L2G+euzdRsUZcK/M6qYf41Dy6Afqa+PxgMEiDto ITEH3Dv+zfzwdeqCuNU0VOGrQZs/vrKOUmU/QDlYL7G8OIg5Ekheq4N+Ay+3EYCROXkstQnf YYxRn5F1oeVeqoh1LgGH7YN9H9LeIajwBD8OgiZDVsmb67DdF6EQtklH0ycBcVodG1zTCfqM AavYMfhldNMBg4vaLh0cJ/3ZXZNIyDlV372GmxSJJiidxDm7E1PkgdfCnHk+pD8YeITmSNyb 7qeU08Hqqh4ui8SSeUp7+yie9zBhJB5vVBJoO5D0MikZAODIDwARAQABzS1BbmRyZSBQcnp5 d2FyYSAoQVJNKSA8YW5kcmUucHJ6eXdhcmFAYXJtLmNvbT7CwXsEEwECACUCGwMGCwkIBwMC BhUIAgkKCwQWAgMBAh4BAheABQJTWSV8AhkBAAoJEAL1yD+ydue63REP/1tPqTo/f6StS00g NTUpjgVqxgsPWYWwSLkgkaUZn2z9Edv86BLpqTY8OBQZ19EUwfNehcnvR+Olw+7wxNnatyxo D2FG0paTia1SjxaJ8Nx3e85jy6l7N2AQrTCFCtFN9lp8Pc0LVBpSbjmP+Peh5Mi7gtCBNkpz KShEaJE25a/+rnIrIXzJHrsbC2GwcssAF3bd03iU41J1gMTalB6HCtQUwgqSsbG8MsR/IwHW XruOnVp0GQRJwlw07e9T3PKTLj3LWsAPe0LHm5W1Q+euoCLsZfYwr7phQ19HAxSCu8hzp43u zSw0+sEQsO+9wz2nGDgQCGepCcJR1lygVn2zwRTQKbq7Hjs+IWZ0gN2nDajScuR1RsxTE4WR lj0+Ne6VrAmPiW6QqRhliDO+e82riI75ywSWrJb9TQw0+UkIQ2DlNr0u0TwCUTcQNN6aKnru ouVt3qoRlcD5MuRhLH+ttAcmNITMg7GQ6RQajWrSKuKFrt6iuDbjgO2cnaTrLbNBBKPTG4oF D6kX8Zea0KvVBagBsaC1CDTDQQMxYBPDBSlqYCb/b2x7KHTvTAHUBSsBRL6MKz8wwruDodTM 4E4ToV9URl4aE/msBZ4GLTtEmUHBh4/AYwk6ACYByYKyx5r3PDG0iHnJ8bV0OeyQ9ujfgBBP B2t4oASNnIOeGEEcQ2rjzsFNBFNPCKMBEACm7Xqafb1Dp1nDl06aw/3O9ixWsGMv1Uhfd2B6 it6wh1HDCn9HpekgouR2HLMvdd3Y//GG89irEasjzENZPsK82PS0bvkxxIHRFm0pikF4ljIb 6tca2sxFr/H7CCtWYZjZzPgnOPtnagN0qVVyEM7L5f7KjGb1/o5EDkVR2SVSSjrlmNdTL2Rd zaPqrBoxuR/y/n856deWqS1ZssOpqwKhxT1IVlF6S47CjFJ3+fiHNjkljLfxzDyQXwXCNoZn BKcW9PvAMf6W1DGASoXtsMg4HHzZ5fW+vnjzvWiC4pXrcP7Ivfxx5pB+nGiOfOY+/VSUlW/9 GdzPlOIc1bGyKc6tGREH5lErmeoJZ5k7E9cMJx+xzuDItvnZbf6RuH5fg3QsljQy8jLlr4S6 8YwxlObySJ5K+suPRzZOG2+kq77RJVqAgZXp3Zdvdaov4a5J3H8pxzjj0yZ2JZlndM4X7Msr P5tfxy1WvV4Km6QeFAsjcF5gM+wWl+mf2qrlp3dRwniG1vkLsnQugQ4oNUrx0ahwOSm9p6kM CIiTITo+W7O9KEE9XCb4vV0ejmLlgdDV8ASVUekeTJkmRIBnz0fa4pa1vbtZoi6/LlIdAEEt PY6p3hgkLLtr2GRodOW/Y3vPRd9+rJHq/tLIfwc58ZhQKmRcgrhtlnuTGTmyUqGSiMNfpwAR AQABwsFfBBgBAgAJBQJTTwijAhsMAAoJEAL1yD+ydue64BgP/33QKczgAvSdj9XTC14wZCGE U8ygZwkkyNf021iNMj+o0dpLU48PIhHIMTXlM2aiiZlPWgKVlDRjlYuc9EZqGgbOOuR/pNYA JX9vaqszyE34JzXBL9DBKUuAui8z8GcxRcz49/xtzzP0kH3OQbBIqZWuMRxKEpRptRT0wzBL O31ygf4FRxs68jvPCuZjTGKELIo656/Hmk17cmjoBAJK7JHfqdGkDXk5tneeHCkB411p9WJU vMO2EqsHjobjuFm89hI0pSxlUoiTL0Nuk9Edemjw70W4anGNyaQtBq+qu1RdjUPBvoJec7y/ EXJtoGxq9Y+tmm22xwApSiIOyMwUi9A1iLjQLmngLeUdsHyrEWTbEYHd2sAM2sqKoZRyBDSv ejRvZD6zwkY/9nRqXt02H1quVOP42xlkwOQU6gxm93o/bxd7S5tEA359Sli5gZRaucpNQkwd KLQdCvFdksD270r4jU/rwR2R/Ubi+txfy0dk2wGBjl1xpSf0Lbl/KMR5TQntELfLR4etizLq Xpd2byn96Ivi8C8u9zJruXTueHH8vt7gJ1oax3yKRGU5o2eipCRiKZ0s/T7fvkdq+8beg9ku fDO4SAgJMIl6H5awliCY2zQvLHysS/Wb8QuB09hmhLZ4AifdHyF1J5qeePEhgTA+BaUbiUZf i4aIXCH3Wv6K Organization: ARM Ltd. Message-ID: Date: Wed, 15 Apr 2020 17:05:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 15/04/2020 16:43, Ard Biesheuvel wrote: Hi Ard, > On Tue, 7 Apr 2020 at 17:15, Alexandru Elisei wrote: >> >> Hi, >> >> I've tested this patch by running badblocks and fio on a flash device inside a >> guest, everything worked as expected. >> >> I've also looked at the flowcharts for device operation from Intel Application >> Note 646, pages 12-21, and they seem implemented correctly. >> >> A few minor issues below. >> >> On 2/21/20 4:55 PM, Andre Przywara wrote: >>> From: Raphael Gault >>> >>> The EDK II UEFI firmware implementation requires some storage for the EFI >>> variables, which is typically some flash storage. >>> Since this is already supported on the EDK II side, we add a CFI flash >>> emulation to kvmtool. >>> This is backed by a file, specified via the --flash or -F command line >>> option. Any flash writes done by the guest will immediately be reflected >>> into this file (kvmtool mmap's the file). >>> The flash will be limited to the nearest power-of-2 size, so only the >>> first 2 MB of a 3 MB file will be used. >>> >>> This implements a CFI flash using the "Intel/Sharp extended command >>> set", as specified in: >>> - JEDEC JESD68.01 >>> - JEDEC JEP137B >>> - Intel Application Note 646 >>> Some gaps in those specs have been filled by looking at real devices and >>> other implementations (QEMU, Linux kernel driver). >>> >>> At the moment this relies on DT to advertise the base address of the >>> flash memory (mapped into the MMIO address space) and is only enabled >>> for ARM/ARM64. The emulation itself is architecture agnostic, though. >>> >>> This is one missing piece toward a working UEFI boot with kvmtool on >>> ARM guests, the other is to provide writable PCI BARs, which is WIP. >>> > > I have given this a spin with UEFI built for kvmtool, and it appears > to be working correctly. However, I noticed that it is intolerably > slow, which seems to be caused by the fact that both array mode and > command mode (or whatever it is called in the CFI spec) are fully > emulated, whereas in the QEMU implementation (for instance), the > region is actually exposed to the guest using a read-only KVM memslot > in array mode, and so the read accesses are made natively. Yes, I have been thinking about this, but didn't implement it this way for the following reasons: 1) The use case here is pure UEFI firmware load, which should not be too much affected by performance. At least this what I was thinking so far. Your "intolerably slow" make me wonder if this assumption is not true. Can you elaborate on that? Do you have any numbers? Is that due to the trapping or something else? 2) As you mentioned, we need to switch between trapping and mapping, upon the guest switching between array mode and command mode. So that just adds complexity. Given 1) it didn't seem worth to do. > It is also causing problems in the UEFI implementation, as we can no > longer use unaligned accesses to read from the region, which is > something the code currently relies on (and which works fine on actual > hardware as long as you use normal non-cacheable mappings) So this is something I was discussing with Sami about already: It seems to me that a parallel memory mapped flash chip is actually a device, just with the twist of behaving with normal (ROM) memory semantics under certain circumstances. So for write accesses and read access in any of the query modes we would definitely need to use device memory and MMIO accessors, otherwise the compiler could mess up the carefully crafted access semantics. So does EDK-2 use separate mappings for both cases? Does it make sure to not access the array when being in command mode? I couldn't find any trace of two mappings in the Linux driver, IIRC. > Are there any plans to implement this as well? I am aware that this is > a big ask, but for the general utility of this feature, I think it is > rather important. I wasn't aware that this has a significant impact, so avoided the added complexity. I doesn't sound like a big deal, though, so I might have a look at it. Cheers, Andre