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Re: [Xen-devel] yanked share problem

Unsharing the page doesn't forcibly revoke other domain's mappings to it, it 
just removes their right to create mappings.  DomU_A in your scenario 
wouldn't be able to cause the fault in DomU_B, the mapping to the page would 
be there until domU_B had finished with it.

The moral of the story is: don't grant pages to people who might not give them 
back ;-)


On Tuesday 13 December 2005 23:05, King, Steven R wrote:
> Hi Folks,
> Let's imagine we have two domains, DomU_A and DomU_B.  Being DomU's, the
> two domains don't trust each other, but still desire to safely setup a
> shared memory page.
> The scenario is the following:
> DomU_A acquires a grant reference and shares a page to DomU_B.
> DomU_B gets the grant reference passed from A and maps the shared page.
> DomU_A then, due to bug or badness, unshares the page without telling
> DomU_B.
> DomU_B faults on the next access to the mapped but unshared page.
> Since one DomU causing a fault in another DomU is unacceptable, the two
> domains cannot share memory.  Have I missed something?  I would much
> appreciate being set straight on this.
> Thanks,
> -steve
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