Re: [Xen-devel] Page tables in Xen

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> In my understanding, in PV, page table is allocated within guest OS,
> however, every update will go through xen via explicit hypercalls.
> in HVM, those update will be intercepted by xen.

In PV, explicit hypercalls are not always used to update the pagetables.  
Using the "writeable pagetables" API it's possible to update the pagetables 
simply by writing to the pagetable memory (Xen then traps this and does the 
appropriate validation before applying the update).

These days, explicit hypercalls are still used for batching updates for 
performance reasons (places where trapping lots of writeable pagetable 
updates would cause a performance hit).

Cheers,
Mark

> Please correct me if I'm wrong.
>
> On Nov 28, 2007 5:49 AM, Haifeng He <hehaifeng2nd@xxxxxxxxx> wrote:
> > Hi,
> >
> > I have a question about memory page tables in Xen. As far as I
> > understood, every modification
> > to page table will go through Xen(hypervisor). Is it so that all page
> > tables are actually allocated
> > in Xen(hypervisor) instead of guest OS(domain)? Also, is it the case
> > that Xen(hypervisor) needs to
> > maintain a page table for each process running in every domain?
> >
> > Thanks
> >
> > Haifeng
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel



-- 
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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