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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 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 0776EC31E40 for ; Sat, 3 Aug 2019 18:05:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C1FAD21726 for ; Sat, 3 Aug 2019 18:05:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564855534; bh=NvLz+V5uiaEIZFYvMNrg/1o0YQBwMMp7TsyzgawILvs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=oGzRtGs84MYxwCAmiu58PadnEgrYmUiD7wAXesoLn/IRV3sJ/9SNqmqsDCAW6Og6/ Dh2/ElPEn09S/yVlbj9WPWJGUxmBDmTLteqZFzKtG15wV9d50U5lvvjMJ57gxpey3s dJfTdsrCoI9SwImVm28p6pzDpj4QVkP3GSgtQdFM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728531AbfHCSFd (ORCPT ); Sat, 3 Aug 2019 14:05:33 -0400 Received: from inca-roads.misterjones.org ([213.251.177.50]:48507 "EHLO inca-roads.misterjones.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728366AbfHCSFd (ORCPT ); Sat, 3 Aug 2019 14:05:33 -0400 Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why) by cheepnis.misterjones.org with esmtpsa (TLSv1.2:AES256-GCM-SHA384:256) (Exim 4.80) (envelope-from ) id 1htyPF-0002A1-0t; Sat, 03 Aug 2019 20:05:25 +0200 Date: Sat, 3 Aug 2019 19:05:22 +0100 From: Marc Zyngier To: Steven Price Cc: Catalin Marinas , Paolo Bonzini , Radim =?UTF-8?B?S3LEjW3DocWZ?= , Russell King , Will Deacon , James Morse , Julien Thierry , Suzuki K Pouloze , kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/9] arm64: Stolen time support Message-ID: <20190803190522.5fec8f7d@why> In-Reply-To: <20190802145017.42543-1-steven.price@arm.com> References: <20190802145017.42543-1-steven.price@arm.com> Organization: Approximate X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2 Aug 2019 15:50:08 +0100 Steven Price wrote: Hi Steven, > This series add support for paravirtualized time for arm64 guests and > KVM hosts following the specification in Arm's document DEN 0057A: > > https://developer.arm.com/docs/den0057/a > > It implements support for stolen time, allowing the guest to > identify time when it is forcibly not executing. > > It doesn't implement support for Live Physical Time (LPT) as there are > some concerns about the overheads and approach in the above > specification, and I expect an updated version of the specification to > be released soon with just the stolen time parts. Thanks for posting this. My current concern with this series is around the fact that we allocate memory from the kernel on behalf of the guest. It is the first example of such thing in the ARM port, and I can't really say I'm fond of it. x86 seems to get away with it by having the memory allocated from userspace, why I tend to like more. Yes, put_user is more expensive than a straight store, but this isn't done too often either. What is the rational for your current approach? Thanks, M. -- Without deviation from the norm, progress is not possible. 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=-2.5 required=3.0 tests=MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 B818BC433FF for ; Sat, 3 Aug 2019 18:05:35 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 4F15A206A2 for ; Sat, 3 Aug 2019 18:05:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F15A206A2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id C24E64A567; Sat, 3 Aug 2019 14:05:34 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id O2zNujYzDewt; Sat, 3 Aug 2019 14:05:33 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id BC0D94A54E; Sat, 3 Aug 2019 14:05:33 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id EC2BA4A54E for ; Sat, 3 Aug 2019 14:05:31 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id TXqdKB12vHIt for ; Sat, 3 Aug 2019 14:05:31 -0400 (EDT) Received: from inca-roads.misterjones.org (inca-roads.misterjones.org [213.251.177.50]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id E5C664A4A9 for ; Sat, 3 Aug 2019 14:05:30 -0400 (EDT) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why) by cheepnis.misterjones.org with esmtpsa (TLSv1.2:AES256-GCM-SHA384:256) (Exim 4.80) (envelope-from ) id 1htyPF-0002A1-0t; Sat, 03 Aug 2019 20:05:25 +0200 Date: Sat, 3 Aug 2019 19:05:22 +0100 From: Marc Zyngier To: Steven Price Subject: Re: [PATCH 0/9] arm64: Stolen time support Message-ID: <20190803190522.5fec8f7d@why> In-Reply-To: <20190802145017.42543-1-steven.price@arm.com> References: <20190802145017.42543-1-steven.price@arm.com> Organization: Approximate X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false Cc: kvm@vger.kernel.org, Catalin Marinas , linux-doc@vger.kernel.org, Russell King , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Fri, 2 Aug 2019 15:50:08 +0100 Steven Price wrote: Hi Steven, > This series add support for paravirtualized time for arm64 guests and > KVM hosts following the specification in Arm's document DEN 0057A: > > https://developer.arm.com/docs/den0057/a > > It implements support for stolen time, allowing the guest to > identify time when it is forcibly not executing. > > It doesn't implement support for Live Physical Time (LPT) as there are > some concerns about the overheads and approach in the above > specification, and I expect an updated version of the specification to > be released soon with just the stolen time parts. Thanks for posting this. My current concern with this series is around the fact that we allocate memory from the kernel on behalf of the guest. It is the first example of such thing in the ARM port, and I can't really say I'm fond of it. x86 seems to get away with it by having the memory allocated from userspace, why I tend to like more. Yes, put_user is more expensive than a straight store, but this isn't done too often either. What is the rational for your current approach? Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 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 15DAFC32750 for ; Sat, 3 Aug 2019 18:05:36 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 DFB5F206A2 for ; 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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1htyPP-0006EL-0k; Sat, 03 Aug 2019 18:05:35 +0000 Received: from inca-roads.misterjones.org ([213.251.177.50]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1htyPL-0006E1-Qj for linux-arm-kernel@lists.infradead.org; Sat, 03 Aug 2019 18:05:33 +0000 Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why) by cheepnis.misterjones.org with esmtpsa (TLSv1.2:AES256-GCM-SHA384:256) (Exim 4.80) (envelope-from ) id 1htyPF-0002A1-0t; Sat, 03 Aug 2019 20:05:25 +0200 Date: Sat, 3 Aug 2019 19:05:22 +0100 From: Marc Zyngier To: Steven Price Subject: Re: [PATCH 0/9] arm64: Stolen time support Message-ID: <20190803190522.5fec8f7d@why> In-Reply-To: <20190802145017.42543-1-steven.price@arm.com> References: <20190802145017.42543-1-steven.price@arm.com> Organization: Approximate X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190803_110532_013890_CEAB0CA8 X-CRM114-Status: GOOD ( 12.08 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, Radim =?UTF-8?B?S3LEjW3DocWZ?= , Catalin Marinas , Suzuki K Pouloze , linux-doc@vger.kernel.org, Russell King , linux-kernel@vger.kernel.org, James Morse , linux-arm-kernel@lists.infradead.org, Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, Julien Thierry Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 2 Aug 2019 15:50:08 +0100 Steven Price wrote: Hi Steven, > This series add support for paravirtualized time for arm64 guests and > KVM hosts following the specification in Arm's document DEN 0057A: > > https://developer.arm.com/docs/den0057/a > > It implements support for stolen time, allowing the guest to > identify time when it is forcibly not executing. > > It doesn't implement support for Live Physical Time (LPT) as there are > some concerns about the overheads and approach in the above > specification, and I expect an updated version of the specification to > be released soon with just the stolen time parts. Thanks for posting this. My current concern with this series is around the fact that we allocate memory from the kernel on behalf of the guest. It is the first example of such thing in the ARM port, and I can't really say I'm fond of it. x86 seems to get away with it by having the memory allocated from userspace, why I tend to like more. Yes, put_user is more expensive than a straight store, but this isn't done too often either. What is the rational for your current approach? Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel