Re: [Xen-devel] Walking an HVM's shadow page tables and other memory management questions.

[Keir Fraser <keir@xxxxxxxxxxxxx>]

The phys-to-machine mechanism needs to be taught about foreign mappings. Currently it will always assume that the pages mapped into the p2m belong to the local domain. 

For encoding I would suggest the p2m entries have PAGE_PRESENT clear and then use some special encoding of the N-1 other bits to indicate a foreign page. I expect then shadow code may need modifying to pass around a foreign domain pointer in some contexts.

 -- Keir

On 6/7/07 20:09, "Roger Cruz" <rcruz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> It looks like get_page_and_type is returning 0.
>  
> (XEN) mm.c:633:d3 l1e_get_flags(l1e) =0x63, shadow_mode_external(d)= 0x4000, current->domain=0x3,get_page_and_type=0x0, get_page(page, d)=0x0
> (XEN) mm.c:639:d3 Error getting mfn 14f0d4 (pfn 1697) from L1 entry 000000014f0d4063 for dom3
>  
> Domain 2 is the grantor and Domain 3 is the grantee in this example.  It appears to me that it is failing because dom3 is not the owner of the shared page
>  
>        if ( unlikely((x & PGC_count_mask) == 0) ||  /* Not allocated? */
>             unlikely((nx & PGC_count_mask) == 0) || /* Count overflow? */
>             unlikely(d != _domain) )               /* Wrong owner? */
>  
> Any suggestions?




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