RE: [Xen-devel] [patch] more correct pfn_valid()

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

>    #define pfn_valid(_pfn)     ((_pfn) < max_page)
> 
> Since max_page is now above the out-of-range io, the 
> pfn_valid() returns "valid". And hence get_page() is called, 
> but returns an error given that the page count is zero ("not 
> allocated") which ultimately ends up that the ioremap() for 
> several device drivers fails with ENOMEM.
> 
> While attached patch fixes this problem (from empirical 
> evidence), there may be a better solution.

I think the best fix is to have the frame_table cover the whole of
physical ram, and then mark non-ram pages in the frame_table.

To save some memory, we could map the frame_table in virtual address
space, then use __get_user when reading from it (a fault indicates a
non-ram page too)

Best,
Ian

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