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 8D297C3279B for ; Fri, 6 Jul 2018 13:49:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4E0C123E08 for ; Fri, 6 Jul 2018 13:49:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E0C123E08 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 S1754098AbeGFNtg (ORCPT ); Fri, 6 Jul 2018 09:49:36 -0400 Received: from foss.arm.com ([217.140.101.70]:37138 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753683AbeGFNtf (ORCPT ); Fri, 6 Jul 2018 09:49:35 -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 91C83ED1; Fri, 6 Jul 2018 06:49:34 -0700 (PDT) Received: from [10.1.206.73] (en101.cambridge.arm.com [10.1.206.73]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0F4C93F5AD; Fri, 6 Jul 2018 06:49:31 -0700 (PDT) Subject: Re: [PATCH v3 15/20] kvm: arm/arm64: Allow tuning the physical address size for VM To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, james.morse@arm.com, marc.zyngier@arm.com, cdall@kernel.org, eric.auger@redhat.com, julien.grall@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> <20180704155104.GN4828@arm.com> <12d1832a-1a13-7dd4-662b-addf58400789@arm.com> From: Suzuki K Poulose Message-ID: Date: Fri, 6 Jul 2018 14:49:30 +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: <12d1832a-1a13-7dd4-662b-addf58400789@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/07/18 23:03, Suzuki K Poulose wrote: > On 07/04/2018 04:51 PM, Will Deacon wrote: >> Hi Suzuki, >> >> On Fri, Jun 29, 2018 at 12:15:35PM +0100, 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. >>> >>> Cc: Marc Zyngier >>> Cc: Christoffer Dall >>> Cc: Peter Maydel >>> Cc: Paolo Bonzini >>> Cc: Radim Krčmář >>> Signed-off-by: Suzuki K Poulose >>> --- >>>   arch/arm/include/asm/kvm_mmu.h   |  2 ++ >>>   arch/arm64/include/asm/kvm_arm.h | 10 +++------- >>>   arch/arm64/include/asm/kvm_mmu.h |  2 ++ >>>   include/uapi/linux/kvm.h         | 10 ++++++++++ >>>   virt/kvm/arm/arm.c               | 24 ++++++++++++++++++++++-- >>>   5 files changed, 39 insertions(+), 9 deletions(-) >> >> [...] >> >>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >>> index 4df9bb6..fa4cab0 100644 >>> --- a/include/uapi/linux/kvm.h >>> +++ b/include/uapi/linux/kvm.h >>> @@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { >>>   #define KVM_S390_SIE_PAGE_OFFSET 1 >>>   /* >>> + * On arm/arm64, machine type can be used to request the physical >>> + * address size for the VM. Bits [7-0] have been reserved for the >>> + * PA size shift (i.e, log2(PA_Size)). For backward compatibility, >>> + * value 0 implies the default IPA size, which is 40bits. >>> + */ >>> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK    0xff >>> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x)        \ >>> +    ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) >> >> This seems like you're allocating quite a lot of bits in a non-extensible >> interface to a fairly esoteric parameter. Would it be better to add another >> ioctl, or condense the number of sizes you support instead? > > As I explained in the other thread, we need the size as soon as the VM > is created. The major challenge is keeping the backward compatibility by > mapping 0 to 40bits. I will give it a thought. Here is one option. We could re-use the {V}TCR_ELx.{I}PS field format, which occupies 3 bits and has the following definitions. (ID_AA64MMFR0_EL1:PARange also has the field definitions, except that the field is 4bits wide, but only 3bits are used) 000 32 bits, 4GB. 001 36 bits, 64GB. 010 40 bits, 1TB. 011 42 bits, 4TB. 100 44 bits, 16TB. 101 48 bits, 256TB. 110 52 bits, 4PB But we need to map 0 => 40bits IPA to make our ABI backward compatible. So we could use the additional one bit to indicate that IPA size is requested in the 3 bits. i.e, machine_type: Bit [2:0] - Requested IPA size. Values follow VTCR_EL2.PS format. Bit [3] - 1 => IPA Size bits (Bits[2:0]) requested. 0 => Not requested The only minor down side is restricting to the predefined values above, which is not a real issue for a VM. Thoughts ? Suzuki