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



(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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