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Re: [Xen-devel] question about running vm change its mem maxsize

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Subject: Re: [Xen-devel] question about running vm change its mem maxsize
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Wed, 21 Mar 2007 04:12:28 +0000
Cc: Daniel Stodden <stodden@xxxxxxxxxx>, tgh <tianguanhua@xxxxxxxxxx>
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> how does hvm guest deal with its physical memory?
> when it boots up, is its physical memory allocated and its virtual
> memory not all allocated or what does its do?

An HVM guest sees a memory model that looks like a normal PC:

The HVM guest's BIOS runs, starts the bootloader.  The bootloader starts the 
OS kernel.  The kernel comes up in real mode, does some setup and switches to 
protected mode[1], then it builds some pagetables and switches to paged mode, 

[1] sometimes (e.g. using grub and an OS supporting the multiboot standard) 
the bootloader may do the real->protected mode switch, but the sequence of 
events is otherwise pretty similar.

Hope that helps.

> could you help me
> Thanks in advance
> >>  that is  during guest-linux
> >> running,it  will  request  some memory  which  it will  get ,for the
> >> guest ,its memory (both its physical memory and its virtual memory)is
> >> dynamical allocated,while raditional linux has its physical memory when
> >> it boot up ,while gets virtual memory dynamically,is it right?
> >
> > yes. see the xen interface manual on this topic, namely the chapters on
> > memory management and the hypercall reference for page table and
> > physical memory management. not sure if this gets entirely clear,
> > though, i sometimes tend to get confused myself. especially guest side
> > vm tends to be complex, but that's quite natural.
> >
> >> could you help me
> >> thanks in advance
> >
> > hth,
> > dns
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Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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