From mboxrd@z Thu Jan  1 00:00:00 1970
From: joro@8bytes.org (Joerg Roedel)
Date: Thu, 10 Nov 2016 15:40:07 +0100
Subject: Summary of LPC guest MSI discussion in Santa Fe
In-Reply-To: <20161109130114.3e17bba9@t450s.home>
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 <20161108163508.1bcae0c2@t450s.home> <58228F71.6020108@redhat.com>
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Message-ID: <20161110144007.GC2078@8bytes.org>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, Nov 09, 2016 at 01:01:14PM -0700, Alex Williamson wrote:
> Well, it's not like QEMU or libvirt stumbling through sysfs to figure
> out where holes could be in order to instantiate a VM with matching
> holes, just in case someone might decide to hot-add a device into the
> VM, at some point, and hopefully they don't migrate the VM to another
> host with a different layout first, is all that much less disgusting or
> foolproof. It's just that in order to dynamically remove a page as a
> possible DMA target we require a paravirt channel, such as a balloon
> driver that's able to pluck a specific page.  In some ways it's
> actually less disgusting, but it puts some prerequisites on
> enlightening the guest OS.  Thanks,

I think it is much simpler if libvirt/qemu just go through all
potentially assignable devices on a system and pre-exclude any addresses
from guest RAM beforehand, rather than doing something like this with
paravirt/ballooning when a device is hot-added. There is no guarantee
that you can take a page away from a linux-guest.


	Joerg