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Date: Tue, 25 Oct 2011 09:18:09 -0400 (EDT)
From: Dave Anderson <anderson@redhat.com>
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Subject: Re: [Qemu-devel] [Question] dump memory when host pci device is
	used by guest
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, Jan Kiszka <jan.kiszka@siemens.com>, "Richard W.M. Jones" <rjones@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>, Avi Kivity <avi@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>



----- Original Message -----
> On 10/25/2011 10:23 AM, Avi Kivity wrote:
> > On 10/25/2011 10:06 AM, Wen Congyang wrote:
> >> Hi, Avi Kivity, Dave Anderson
> >>
> >> I have two questions about it:
> >>
> >> 1. How to know the guest's physical base address in qemu?
> >
> > In fact, it's impossible.
> >
> > Perhaps crash can scan through the core looking for a signature.  Need
> > to be careful since multiple signatures may be detected (a kdump kernel,
> > a kernel image in pagecache, or a nested guest).
> 
> Crash uses a heuristic based on the IDT base to identify the base from
> migrate-to-file output.  It also needs CR3 in order to read from virtual
> address.

Just to clarify -- the need for the IDT base and cr3 is *only* true for 
KVM dumps using the "savevm" format.  

With ELF-format kdumps, the phys_base is simply determined from the PT_LOAD
segment that describes the kernel's __START_KERNEL_map region.  I don't know
why that couldn't be done in this proposed case.  
 
Dave