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=-0.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 371BBC432C0 for ; Mon, 18 Nov 2019 16:27:26 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E91F3218AE for ; Mon, 18 Nov 2019 16:27:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="zQTzjQCf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E91F3218AE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:36592 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iWjs4-0002i7-7n for qemu-devel@archiver.kernel.org; Mon, 18 Nov 2019 11:27:24 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:47284) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iWjr7-0001j3-2x for qemu-devel@nongnu.org; Mon, 18 Nov 2019 11:26:26 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iWjr5-0001KG-C2 for qemu-devel@nongnu.org; Mon, 18 Nov 2019 11:26:24 -0500 Received: from mail-oi1-x242.google.com ([2607:f8b0:4864:20::242]:34878) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1iWjr5-0001Jj-67 for qemu-devel@nongnu.org; Mon, 18 Nov 2019 11:26:23 -0500 Received: by mail-oi1-x242.google.com with SMTP id n16so15868826oig.2 for ; Mon, 18 Nov 2019 08:26:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=XIkGnW1aRZhqvnzNNKG7aAGx1vjkLpHYjgJTUtfIq7s=; b=zQTzjQCfPHL8cSUxxFIptzbn+pteWPqD0rc+uq29QAZYKZPTkbtvDpErjq0Rbh8nMJ KaN+cWOFwgrPfxUbtf1Tdt/TcQOCnSwLhJi8a5PBv0Gxz5Zy0oZB2I+qBfPmoWmfIV22 XIoHho33pfS88oEBvJNsAWOOKQHtec4YjYiZElC9WAi05TDkz5P0x49FGjj/4oiUVfou msBMJCdeRZyTelz4RCkWBKL/EPI11T6mAK8p1162UrwtCJiXP4tZAZrJcLMdMfIMlc1n j/viMZkl0niBfC/pDIqzdcxKdgZ4Su6OC+gJqsrEStfjzto/l1FwBOosJ5C1tItX9o2N 84FA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=XIkGnW1aRZhqvnzNNKG7aAGx1vjkLpHYjgJTUtfIq7s=; b=jnvWv7lCQeXkyHvMaA00T7zXGByvMKRufNG+goefXZkA5mq77fX34qf8A29BWgXaat 14doxwtzds3WjCudf4ZOoGahHswaXTxYmJL0lwIsRgxeJe2fNsNOcDk1B0xOCXIkISOc UTKeWL0F8T0liFyYiEjfkDbJ4slUCnEc9uokm6XXGuDAK7NzKc8MnCJWl9Sjp1Ze+AnG HiPdu/3dUIZL5aSX+fUz3UFz2WCVMoaO9rsHq0dnKlKtZzOcc2QxLNZYaL6znk6tn3VR r9EJdLQtMBisM0ijeJY7Clsm8yfl5p3IQDEzM5KSMkdZ9Zgdrxb04UNzIdTSl2vUYKLk RzlA== X-Gm-Message-State: APjAAAW2s4+1nyIE8twKnzv+Aq3HGI4oI3uBTK6CnqagnpQLOEPmXKOl wILzJ7gH0d5uXurmDtYoIuKhY5YkC5oykND1J5Qd/A== X-Google-Smtp-Source: APXvYqzMMBcq8p0iHwjVeLutW1NH6INXLSoD0KnncDtLz0IsKh7lZ9N4dlh16MXdp/8uyPbx4f2H2JcenB8O3lUr3cA= X-Received: by 2002:aca:cf12:: with SMTP id f18mr19906448oig.48.1574094381951; Mon, 18 Nov 2019 08:26:21 -0800 (PST) MIME-Version: 1.0 References: <20191017044232.27601-1-richard.henderson@linaro.org> In-Reply-To: <20191017044232.27601-1-richard.henderson@linaro.org> From: Peter Maydell Date: Mon, 18 Nov 2019 16:26:10 +0000 Message-ID: Subject: Re: [PATCH 0/4] target/arm vector improvements To: Richard Henderson Content-Type: text/plain; charset="UTF-8" X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:4864:20::242 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-arm , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 17 Oct 2019 at 05:42, Richard Henderson wrote: > > The first patch has been seen before. > > https://patchwork.ozlabs.org/patch/1115039/ > > It had a bug and I didn't fix it right away and then forgot. > Fixed now; I had mixed up the operand ordering for aarch32. Since Alex had a nit on patch 1 I'm going to assume you'll respin this series once we're reopen for 5.0 development. > The comment in patch 2 about ARMv8.4-DIT is perhaps a stretch, > but re-reading the pmull instruction description in the current > ARM ARM brought it to mind. > > Since TCG is officially not in the security domain, it's > probably not a bug to just claim to support DIT without > actually doing anything to ensure the algorithms used are in > fact timing independent of the data. > > On the other hand, I expect the bit distribution of stuff > going through these sort of hashing algorithms to approach > 50% 1's and 0's, so I also don't think we gain anything on > average to terminate the loop early. > > Thoughts on DIT specifically? I think we have two plausible choices for DIT: (1) don't implement it, since we can't make the timing guarantees it suggests (2) implement it but not actually change our behaviour: this is technically a lie to the guest, but it means that guest OS handling of the PSTATE.DIT bit etc can be tested At the moment we by default do (1). I think we should probably postpone doing (2) until somebody actually asks us for it. thanks -- PMM