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Re: [Qemu-devel] vm state save/restore question

From: Alexander Graf
Subject: Re: [Qemu-devel] vm state save/restore question
Date: Wed, 20 Jun 2012 02:05:42 +0200

On 20.06.2012, at 01:52, Benjamin Herrenschmidt wrote:

> On Wed, 2012-06-20 at 01:30 +0200, Alexander Graf wrote:
>>> We support the paravirtualized -M pseries in full emu as well, in which
>>> case the hashed page table is handled by qemu itself who implements the
>>> H_ENTER & co hypercalls. So it's very similar, except that qemu doesn't
>>> have to ask the kernel to get a snapshot :-)
>>> So I can flush out the storage format and two stage process inside qemu,
>>> and then bother with the kvm/kernel interface.
>>> Normal "bare metal" operation in qemu (or even KVM "PR") doesn't require
>>> this as in that case the hash table is just a normal part of the guest
>>> memory, it's only an issue when doing paravirtualized guest such as
>>> pseries (aka PAPR).
>> IIRC we still allocate it outside of normal guest memory, so you don't get 
>> the migration for free :).
> You haven't ready my post properly :-)

Ugh. Right. I haven't :). For Non-pseries VMs, the HTAB is always in guest RAM, 
so it's migrated automatically. Only pseries is special in keeping it outside.


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