Re: [Xen-devel] Forwarding page faults from within Xen

[Jacob Gorm Hansen <jacob@xxxxxxxx>]

On Mon, 2004-03-22 at 12:51, Keir Fraser wrote:
> > hi,
> > 

> Well, you need *some* way of executing and informing the domain to
> tell it about the fault. So there has to be *some* pinned
> always-accessible memory to be able to do this. If you get rid of this
> constraint on the guest-OS stack, then you'll still need some other
> memory buffer to store fault info -- there has to be some back
> stop. So I don't think you save yourself any pain.

Hmm, I suppose you are right about that then... I keep forgetting the
price all the luxury features of L4 came at.

> As for network buffers, how would we present the fault to the guest
> OS? The neatest answer to all this that I can see is to use shadow
> page tables and use this to get Xen to log pages as they are dirtied.
> Anything which involves the guest OS itself receiving 'page faults'
> for events which occurred under its feet just sounds hideous to me!
> :-)

Actually, my problem is not as much the network buffer pages, put the
pagetables pointing to them. Right now I identify these and take care of
them specially so that my checkpoint is consistent, but it is a bit
unclear to me what happens if I write-protect them. Will Xen kill me, or
just silently change the protection bits?

Jacob



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