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

[Tim Deegan <tim@xxxxxxx>]

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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