[Xen-devel] Re: [Question] Why code differs in construct_dom0?

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

By deliberately making dom0's p2m mapping discontiguous we can detect bugs
where dom0 is incorrectly assuming pseudophys contiguous memory is machine
contiguous. We had nasty bugs of this sort in dom0's block layer many years
ago.

 -- Keir

On 20/11/08 09:07, "Shan, Haitao" <haitao.shan@xxxxxxxxx> wrote:

> Hi, Keir,
> 
> Please see the code shown below. I don't understand why pfn's definitions are
> different depending on whether NDEBUG is defined or not. Can you tell me why?
>  
>     while ( pfn < nr_pages )
>     {
>         if ( (page = alloc_chunk(d, nr_pages - d->tot_pages)) == NULL )
>             panic("Not enough RAM for DOM0 reservation.\n");
>         while ( pfn < d->tot_pages )
>         {
>             mfn = page_to_mfn(page);
> #ifndef NDEBUG
> #define pfn (nr_pages - 1 - (pfn - (alloc_epfn - alloc_spfn)))
> #endif
>             if ( !is_pv_32on64_domain(d) )
>                 ((unsigned long *)vphysmap_start)[pfn] = mfn;
>             else
>                 ((unsigned int *)vphysmap_start)[pfn] = mfn;
>             set_gpfn_from_mfn(mfn, pfn);
> #undef pfn
>             page++; pfn++;
>         }
>     }
> 
> Best Regards
> Haitao Shan



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