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Re: [Xen-devel] xen crash during Dom0 boot

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] xen crash during Dom0 boot
From: Christoph Egger <Christoph.Egger@xxxxxxx>
Date: Thu, 14 Apr 2011 16:44:20 +0200
Cc: Tim, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Deegan <Tim.Deegan@xxxxxxxxxx>
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On 04/14/11 15:33, Konrad Rzeszutek Wilk wrote:

The reason is that guest_walk_tables() in xen/arch/x86/mm/guest_walk.c  fakes
l1e entries for 2mb pages but not for 1gb pages.
A workaround is to assign the Dom0 not more than 2 GB RAM  via
the dom0_mem  xen boot parameter.

But if you use 4KB pages then the workaround is not neccessary, right?

Right. Same counts for 2MB pages.

This can only be reproduced with Dom0 kernels which use the autotranslation
feature (Linux Dom0 does, NetBSD Dom0 doesn't, don't know about other Dom0).

Autotranslation feature.. you mean that pagetables are not updated via
the Linux kernel, but instead by the Xen hypervisor?

With the autotranslation feature the pv guest does not need to be aware about the fact that the guest physical address space is not the host physical address. Xen maintains a shadow page table for it.

W/o the autotranslation feature the pv guest is aware of it and handles
the translation itself.


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