Re: [Xen-devel] [PATCH 2 of 2] x86/mm: New mem access type to log access

[Tim Deegan <tim@xxxxxxx>]

At 16:58 -0500 on 29 Nov (1322585905), Andres Lagar-Cavilla wrote:
> @@ -1162,10 +1167,13 @@ int p2m_mem_access_check(unsigned long g
>          }
>          else
>          {
> -            /* A listener is not required, so clear the access restrictions 
> */
> -            p2m_lock(p2m);
> -            p2m->set_entry(p2m, gfn, mfn, PAGE_ORDER_4K, p2mt, 
> p2m_access_rwx);
> -            p2m_unlock(p2m);
> +            if ( p2ma != p2m_access_n2rwx )
> +            {
> +                /* A listener is not required, so clear the access 
> restrictions */
> +                p2m_lock(p2m);
> +                p2m->set_entry(p2m, gfn, mfn, PAGE_ORDER_4K, p2mt, 
> p2m_access_rwx);
> +                p2m_unlock(p2m);
> +            }
>              return 1;
>          }

This logic is getting a bit convoluted, and I'm not sure it's correct.
If a page is marked n2rwx and there's no listener, it looks like this
will cause it to spin forever re-taking the fault rather than pausing it
waiting for the listener to attach.

Cheers,

Tim.

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