Re: [XenARM] Xen-ARM and paravirt_ops?

[maheen butt <maheen_butt26@xxxxxxxxx>]

________________________________
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
To: maheen_butt26@xxxxxxxxx 
Cc: Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>; 
xen-arm@xxxxxxxxxxxxxxxxxxx; sbuk.suh@xxxxxxxxxxx; keir@xxxxxxx; 
community.manager@xxxxxxx 
Sent: Friday, August 10, 2012 2:59 PM
Subject: Re: Xen-ARM and paravirt_ops?

On Fri, 10 Aug 2012, maheen butt wrote:
> Hi,
> I came to know from Xen-ARM wiki and other related pages that ARM  port is 
> based on 
> xen-unstable and it can boot a Linux 3.0 based virtual machine (dom 0). for 
> reference
> https://lkml.org/lkml/2011/11/29/265
> 
> As Xen-ARM can boot Linux 3.0, it means that this hypervisor is using 
> paravirt_ops infrastructure of kernel. I want to know that did you explicitly 
> add paravirt_ops support in kernel for ARM?

The xen-unstable based ARM port uses the new virtualization extensions
introduced recently by ARM. Therefore it requires a Cortex-A15 processor
or newer in order to work. On the other hand no paravirt_ops support is
necessary in the kernel, as we are using nested paging in hardware.

What is the relationship between nested paging and paravirt_ops? paravirt_ops 
is 
 hypervisor-agnostic interface between the hypervisor and guest kernels where 
as 
nested paging increase the performance of hardware virtualization by providing 
hardware 
support for page-table virtualization. Its hard for me to understand 
relationship between two.
(the relationship is that if one is present other can be ignored)
will you please explain it.


> As far as I know paravirt_ops is an infrastructure given by Linux kernel to 
> support 
> hypervisor. and http://wiki.xensource.com/xenwiki/XenParavirtOps tells that
> at present paravirt_ops is available for x86_32, x86_64 and ia64 
> architectures.
> If this the case that you have add support of paravirt_ops in Linux kernel 
> for ARM
> architecture then what is the level of complexity for adding this kind of 
> support?

The level of complexity is non-trivial, fortunately we managed to avoid
it.

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