Re: [Xen-devel] remove entry in shadow table

[HANNAS YAYA Issa <issa.hannasyaya@xxxxxxxxxxx>]

Ok
I have no problem with overhead since I remove only 100 pages.
Thank you

Hannas

On Thu, 9 Apr 2015 11:27:16 +0100, Tim Deegan wrote:
> Hi,
>
> At 18:15 +0200 on 06 Apr (1428344115), HANNAS YAYA Issa wrote:
> > I want to remove entry of a given page in the shadow page table so 
> > that
> > when the next time the guest access to the page there is page fault.
> > Here is what I try to do:
> >
> > 1. I have a timer which wake up every 30 seconds and remove entry in
> > the shadow by calling
> > sh_remove_all_mappings(d->vcpu[0], _mfn(page_to_mfn(page)))
> > here "d" is the domain and "page" is the page that I want to remove
> > from the shadow page table.
> > 2. In the function "sh_page_fault()" I get the gmfn and compare it 
> > with
> > the mfn of the page that I removed earlier from the shadow page 
> > table.
> > Is this method correct?
> Yes, though it may be extremely slow if you're doing it for large
> numbers of mfns, since sh_remove_all_mappings() may have to do a
> brute-force search of all PTEs for each one.
>
> You should probably put your check for the gmfn in _sh_propagate(),
> rather than sh_page_fault().  That way it will also see things like
> prefetched mappings.
>
> > I also get this error: "sh error: sh_remove_all_mappings(): can't 
> > find
> > all mappings of mfn"
> That usually means that there's a mapping of that frame from another
> domain.
>
> Tim.

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