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 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 A9733C6778A for ; Mon, 2 Jul 2018 13:14:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 62ABC24DFC for ; Mon, 2 Jul 2018 13:14:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 62ABC24DFC 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 S1752646AbeGBNOL (ORCPT ); Mon, 2 Jul 2018 09:14:11 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:60098 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751626AbeGBNOD (ORCPT ); Mon, 2 Jul 2018 09:14:03 -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 83FA618A; Mon, 2 Jul 2018 06:14:03 -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 EF6533F5AD; Mon, 2 Jul 2018 06:14:00 -0700 (PDT) Subject: Re: [PATCH v3 15/20] kvm: arm/arm64: Allow tuning the physical address size for VM To: Suzuki K Poulose , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, james.morse@arm.com, cdall@kernel.org, eric.auger@redhat.com, julien.grall@arm.com, will.deacon@arm.com, catalin.marinas@arm.com, punit.agrawal@arm.com, qemu-devel@nongnu.org, Peter Maydel , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= References: <1530270944-11351-1-git-send-email-suzuki.poulose@arm.com> <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> From: Marc Zyngier Organization: ARM Ltd Message-ID: Date: Mon, 2 Jul 2018 14:13:59 +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: <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> 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 On 29/06/18 12:15, Suzuki K Poulose wrote: > Allow specifying the physical address size for a new VM via > the kvm_type argument for KVM_CREATE_VM ioctl. This allows > us to finalise the stage2 page table format as early as possible > and hence perform the right checks on the memory slots without > complication. The size is encoded as Log2(PA_Size) in the bits[7:0] > of the type field and can encode more information in the future if > required. The IPA size is still capped at 40bits. Can't we relax this? There is no technical reason (AFAICS) not to allow going down to 36bit IPA if the user has requested it. If we run on a 36bit IPA system, the default would fail. But if the user specified "please give me a 36bit IPA VM", we could satisfy that requirement and allow them to run their stupidly small guest! Thanks, M. -- Jazz is not dead. It just smells funny... From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38358) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fZyeh-00044t-1T for qemu-devel@nongnu.org; Mon, 02 Jul 2018 09:14:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fZyeb-000212-Vf for qemu-devel@nongnu.org; Mon, 02 Jul 2018 09:14:11 -0400 Received: from foss.arm.com ([217.140.101.70]:39320) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fZyeb-00020Q-1k for qemu-devel@nongnu.org; Mon, 02 Jul 2018 09:14:05 -0400 References: <1530270944-11351-1-git-send-email-suzuki.poulose@arm.com> <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> From: Marc Zyngier Message-ID: Date: Mon, 2 Jul 2018 14:13:59 +0100 MIME-Version: 1.0 In-Reply-To: <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3 15/20] kvm: arm/arm64: Allow tuning the physical address size for VM List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Suzuki K Poulose , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, james.morse@arm.com, cdall@kernel.org, eric.auger@redhat.com, julien.grall@arm.com, will.deacon@arm.com, catalin.marinas@arm.com, punit.agrawal@arm.com, qemu-devel@nongnu.org, Peter Maydel , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= On 29/06/18 12:15, Suzuki K Poulose wrote: > Allow specifying the physical address size for a new VM via > the kvm_type argument for KVM_CREATE_VM ioctl. This allows > us to finalise the stage2 page table format as early as possible > and hence perform the right checks on the memory slots without > complication. The size is encoded as Log2(PA_Size) in the bits[7:0] > of the type field and can encode more information in the future if > required. The IPA size is still capped at 40bits. Can't we relax this? There is no technical reason (AFAICS) not to allow going down to 36bit IPA if the user has requested it. If we run on a 36bit IPA system, the default would fail. But if the user specified "please give me a 36bit IPA VM", we could satisfy that requirement and allow them to run their stupidly small guest! Thanks, M. -- Jazz is not dead. It just smells funny... From mboxrd@z Thu Jan 1 00:00:00 1970 From: marc.zyngier@arm.com (Marc Zyngier) Date: Mon, 2 Jul 2018 14:13:59 +0100 Subject: [PATCH v3 15/20] kvm: arm/arm64: Allow tuning the physical address size for VM In-Reply-To: <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> References: <1530270944-11351-1-git-send-email-suzuki.poulose@arm.com> <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 29/06/18 12:15, Suzuki K Poulose wrote: > Allow specifying the physical address size for a new VM via > the kvm_type argument for KVM_CREATE_VM ioctl. This allows > us to finalise the stage2 page table format as early as possible > and hence perform the right checks on the memory slots without > complication. The size is encoded as Log2(PA_Size) in the bits[7:0] > of the type field and can encode more information in the future if > required. The IPA size is still capped at 40bits. Can't we relax this? There is no technical reason (AFAICS) not to allow going down to 36bit IPA if the user has requested it. If we run on a 36bit IPA system, the default would fail. But if the user specified "please give me a 36bit IPA VM", we could satisfy that requirement and allow them to run their stupidly small guest! Thanks, M. -- Jazz is not dead. It just smells funny...