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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 BDFD6C6778C for ; Thu, 5 Jul 2018 14:15:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8260F24112 for ; Thu, 5 Jul 2018 14:15:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8260F24112 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753845AbeGEOPx (ORCPT ); Thu, 5 Jul 2018 10:15:53 -0400 Received: from foss.arm.com ([217.140.101.70]:50576 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753785AbeGEOPv (ORCPT ); Thu, 5 Jul 2018 10:15:51 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6E52318A; Thu, 5 Jul 2018 07:15:51 -0700 (PDT) Received: from [10.1.206.75] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0DDA83F5BA; Thu, 5 Jul 2018 07:15:47 -0700 (PDT) Subject: Re: [kvmtool test PATCH 22/24] kvmtool: arm64: Add support for guest physical address size To: Auger Eric , Julien Grall , Will Deacon Cc: Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, james.morse@arm.com, cdall@kernel.org, catalin.marinas@arm.com, punit.agrawal@arm.com, qemu-devel@nongnu.org References: <1530270944-11351-1-git-send-email-suzuki.poulose@arm.com> <1530270944-11351-23-git-send-email-suzuki.poulose@arm.com> <20180704140943.GF4828@arm.com> <8c9bb3cd-f673-17f3-656f-66b7e14fc73c@arm.com> <20180704155231.GP4828@arm.com> From: Marc Zyngier Organization: ARM Ltd Message-ID: <29208b59-0224-00d2-0e2a-6f53a0cbc963@arm.com> Date: Thu, 5 Jul 2018 15:15:46 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 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 Hi Eric, On 05/07/18 14:46, Auger Eric wrote: > Hi Marc, > > On 07/05/2018 03:20 PM, Marc Zyngier wrote: >> On 05/07/18 13:47, Julien Grall wrote: >>> Hi Will, >>> >>> On 04/07/18 16:52, Will Deacon wrote: >>>> On Wed, Jul 04, 2018 at 04:00:11PM +0100, Julien Grall wrote: >>>>> On 04/07/18 15:09, Will Deacon wrote: >>>>>> On Fri, Jun 29, 2018 at 12:15:42PM +0100, Suzuki K Poulose wrote: >>>>>>> Add an option to specify the physical address size used by this >>>>>>> VM. >>>>>>> >>>>>>> Signed-off-by: Suzuki K Poulose >>>>>>> --- >>>>>>> arm/aarch64/include/kvm/kvm-config-arch.h | 5 ++++- >>>>>>> arm/include/arm-common/kvm-config-arch.h | 1 + >>>>>>> 2 files changed, 5 insertions(+), 1 deletion(-) >>>>>>> >>>>>>> diff --git a/arm/aarch64/include/kvm/kvm-config-arch.h b/arm/aarch64/include/kvm/kvm-config-arch.h >>>>>>> index 04be43d..dabd22c 100644 >>>>>>> --- a/arm/aarch64/include/kvm/kvm-config-arch.h >>>>>>> +++ b/arm/aarch64/include/kvm/kvm-config-arch.h >>>>>>> @@ -8,7 +8,10 @@ >>>>>>> "Create PMUv3 device"), \ >>>>>>> OPT_U64('\0', "kaslr-seed", &(cfg)->kaslr_seed, \ >>>>>>> "Specify random seed for Kernel Address Space " \ >>>>>>> - "Layout Randomization (KASLR)"), >>>>>>> + "Layout Randomization (KASLR)"), \ >>>>>>> + OPT_INTEGER('\0', "phys-shift", &(cfg)->phys_shift, \ >>>>>>> + "Specify maximum physical address size (not " \ >>>>>>> + "the amount of memory)"), >>>>>> >>>>>> Given that this is a shift value, I think the help message could be more >>>>>> informative. Something like: >>>>>> >>>>>> "Specify maximum number of bits in a guest physical address" >>>>>> >>>>>> I think I'd actually leave out any mention of memory, because this does >>>>>> actually have an effect on the amount of addressable memory in a way that I >>>>>> don't think we want to describe in half of a usage message line :) >>>>> Is there any particular reasons to expose this option to the user? >>>>> >>>>> I have recently sent a series to allow the user to specify the position >>>>> of the RAM [1]. With that series in mind, I think the user would not really >>>>> need to specify the maximum physical shift. Instead we could automatically >>>>> find it. >>>> >>>> Marc makes a good point that it doesn't help for MMIO regions, so I'm trying >>>> to understand whether we can do something differently there and avoid >>>> sacrificing the type parameter. >>> >>> I am not sure to understand this. kvmtools knows the memory layout >>> (including MMIOs) of the guest, so couldn't it guess the maximum >>> physical shift for that? >> >> That's exactly what Will was trying to avoid, by having KVM to compute >> the size of the IPA space based on the registered memslots. We've now >> established that it doesn't work, so what we need to define is: >> >> - whether we need another ioctl(), or do we carry on piggy-backing on >> the CPU type, > kvm type I guess I really meant target here. Whatever you pass as a "-cpu" on your QEMU command line. >> - assuming the latter, whether we can reduce the number of bits used in >> the ioctl parameter by subtly encoding the IPA size. > Getting benefit from your Freudian slip, how should guest CPU PARange > and maximum number of bits in a guest physical address relate? Freudian? I'm not on the sofa yet... ;-) > My understanding is they are not correlated at the moment and our guest > PARange is fixed at the moment. But shouldn't they? > > On Intel there is > qemu-system-x86_64 -M pc,accel=kvm -cpu SandyBridge,phys-bits=36 > or > qemu-system-x86_64 -M pc,accel=kvm -cpu SandyBridge,host-phys-bits=true > > where phys-bits, as far as I understand has a a similar semantics as the > PARange. I think there is value in having it global, just like on x86. We don't really support heterogeneous guests anyway. Independently, we should also repaint/satinize PARange so that the guest observes the same thing, no matter what CPU it runs on (an A53/A57 system could be confusing in that respect). Thanks, M. -- Jazz is not dead. It just smells funny...