Re: [Xen-devel] [PATCH] fix memory exchange hypercall.

On Thu, Mar 15, 2007 at 01:58:56PM +0000, Keir Fraser wrote:

> > - If the p2m entry is cleared which isn't followed by
> >   clearing PGC_allocaed and put_page() without any recording,
> >   there is no easy way to free the page until domain destruction.
> 
> This is true. Arguably guest_physmap_add_page() should test-and-clear
> PGC_allocated if there was already a page mapped at that address. Or it
> should fail. Or we should expect the guest not to do something this silly.
> 
> Really the correct answer is not immediately clear. I guess the first option
> makes most sense though, perhaps with a gdprintk(XENLOG_WARNING).

The ia64 p2m already adopted the first option without warning.
So the guest_physmap_remove_page() depends on PGC_allocated bit.
What's the expected behavior of guset_physmap_remove_page() with
PGC_allocated? It shouldn't touch the bit?

Thanks a lot for your clarification.
-- 
yamahata

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