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Re: [Xen-devel] [RFC Patch] Support for making an E820 PCI hole in tools

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC Patch] Support for making an E820 PCI hole in toolstack (xl + xm)
From: Keir Fraser <keir@xxxxxxx>
Date: Mon, 15 Nov 2010 17:48:55 +0000
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, bruce.edge@xxxxxxxxx, gianni.tedesco@xxxxxxxxxx, stefano.stabellini@xxxxxxxxxxxxx
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Thread-topic: [Xen-devel] [RFC Patch] Support for making an E820 PCI hole in toolstack (xl + xm)
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On 15/11/2010 17:03, "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx> wrote:

> On Sat, Nov 13, 2010 at 07:40:30AM +0000, Keir Fraser wrote:
>> Why doesn't the guest punch its own hole, by relocating RAM above 4GB?
>  1). Did not work for me - I am not sure why but I had the hardest time do
>      hypervisor_populate_physmap - it would just hang the guest.

For a PV guest you don't need to do any alloc/free/move memory hypercalls.
You rewrite your own p2m to relocate mfns where you want them in pfn space.
Then some hypercalls just to update the m2p array to match.

>  2). It is much simple to parse the E820 in the Linux kernel than actually
>      creating new E820 entries in the kernel (hypercall), making a bunch of
>      hypervisor calls that unmap, then remap the space, filling out the P2M
>      with INVALID_MFN, and doing all of that before the "real" Linux kernel
>      actually starts (all would have to be done in xen_start_kernel).
>      I have a sinking feeling tha the upstream community would not like it
>      this that much.

Well it is all quite Xen specific, so I'm surprised.

>> That's what all HVM guests do (in hvmloader).
>   3). Which is also part of the Xen tool-stack.
> Keir, I think you posted it at some point - was there a standard 'indent'
> incantention for the tools/libxc StyleGuide (which is similar to to the xen/*
> one) - I can't find it in my mail archive...

I think someone else worked one out, but I don't have it to hand I'm afraid.

 -- Keir

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