linux-kernel - Re: [kvmtool test PATCH 24/24] kvmtool: arm: Add support for creating VM with PA size

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Message-ID: <c04ac446-ec16-6ec9-383a-e93f0e2d7275@redhat.com>
Date:   Thu, 5 Jul 2018 09:58:50 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Peter Maydell <peter.maydell@...aro.org>,
        Will Deacon <will.deacon@....com>
Cc:     Christoffer Dall <cdall@...nel.org>,
        kvm-devel <kvm@...r.kernel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Punit Agrawal <punit.agrawal@....com>,
        lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
        QEMU Developers <qemu-devel@...gnu.org>,
        kvmarm@...ts.cs.columbia.edu,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [kvmtool test PATCH 24/24] kvmtool: arm: Add support for creating
 VM with PA size

Hi,

On 07/05/2018 09:51 AM, Peter Maydell wrote:
> On 4 July 2018 at 16:51, Will Deacon <will.deacon@....com> wrote:
>> On Wed, Jul 04, 2018 at 03:41:18PM +0100, Marc Zyngier wrote:
>>> Not really. Let's say I want my IPA space split in two: memory covers
>>> the low 47 bit, and I want MMIO spanning the top 47 bit. With your
>>> scheme, you'd end-up with a 47bit IPA space, while you really want 48
>>> bits (MMIO space implemented by userspace isn't registered to the
>>> kernel).
>>
>> That still sounds quite niche for a VM. Does QEMU do that?
> 
> Not at 47 bits, but we have RAM up to the 256GB mark, and
> MMIO above that (including a large PCI window), so the general
> arrangement of having the top end of the IPA space not
> necessarily be things we've told the kernel about definitely
> exists.

Is this document (2012) still a reference document?
http://infocenter.arm.com/help/topic/com.arm.doc.den0001c/DEN0001C_principles_of_arm_memory_maps.pdf
(especially Fig 5?)

Peter, comments in QEMU hw/arm/virt.c suggested next RAM chunk should be
added at 2TB. This doc suggests to put it at 8TB. I understand the PA
memory map only is suggested but shouldn't we align?

Thanks

Eric

> 
> thanks
> -- PMM
> _______________________________________________
> kvmarm mailing list
> kvmarm@...ts.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
> 

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