Re: [Xen-devel] How to boot domU and dom0 from a device tree

From: Julien Grall <julien.grall@arm.com>
To: Stefano Stabellini <sstabellini@kernel.org>,
	Denis Obrezkov <denisobrezkov@gmail.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
	Hunyue Yau <hy-gsoc@hy-research.com>,
	Iain Hunter <drhunter95@gmail.com>
Subject: Re: [Xen-devel] How to boot domU and dom0 from a device tree
Date: Wed, 12 Jun 2019 12:26:03 +0100	[thread overview]
Message-ID: <dca4af7b-6591-cb01-8e75-32438097f65a@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1906111515000.13737@sstabellini-ThinkPad-T480s>

(Moving from xen-users to xen-devel).

On 11/06/2019 23:18, Stefano Stabellini wrote:
> I managed to reproduced the issue, and I know how to get past it.  Try
> using the raw kernel Image (arch/arm64/boot/Image) instead of Image.gz
> for dom0 and domU. That fixed it for me.
> 
> Julien, I didn't manage to figure out what the issue is exactly, but it
> looks like Image.gz loading is broken at the moment.

Do you mean Image.gz is broken from DomU? Because per the log provided by Denis, 
this is working perfectly for Dom0 as we don't create domain in parallel.

By reading the code I can already spot the reason of the first issue reported by 
Denis. For reminder, this is when Dom0 and DomU are using the same module 
address for the gzip Image.

This is because when probing the kernel for Dom0, the module will get 
uncompressed and the module start/end will be updated to point to the uncompress 
version. Because of that, the probe for DomU kernel will not be able to find the 
module (the start addressed changed).

In this case, I think we only want to uncompress the module one time to avoid 
wasting memory. The solution I have in mind requires some rework in Xen, I would 
actually start by probing the information for all the domains, then uncompress 
the kernels modules, and then finish to build the domain.

For the out of memory problem discussed in this e-mail, I think the problem is 
not because of lack of memory in DomU. The problem is related to the 
inflate/gunzip the code. The code is using an heap (see perform_gunzip) where it 
allocates memory from.

I am assuming the kernels for Dom0 and DomU are exactly the same but they are 
coming from different address. Am I correct? If so, I am a bit unsure this 
worked the first time and not the second time. This probably want some debugging 
to understand the problem. Denis, Stefano, can one of you look at it?

Cheers,

-- 
Julien Grall

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