Re: [Xen-devel] [PATCH 1 of 2] x86/mm: When mem event automatically promotes access rights, let other subsystems know

[Tim Deegan <tim@xxxxxxx>]

At 08:39 -0800 on 01 Dec (1322728771), Andres Lagar-Cavilla wrote:
> > I wonder whether, rather than trying to enumerate all the acceptable
> > cases here, you could just remember that p2m_mem_access_check() changed
> > something and always return 1 in that case.
> >
> That's the behavior without this patch, isn't it?

Yes, but that's not the _interesting_ change in this patch. :) 
The interesting thing is that you can upgrade the access rights and also
pass the fault to the mmio emulator without returning and retrying in
between. 

That is, I thin the change from 

    if (access fixup) return 1
    handle MMIO
    ...
    return 0 /* unhandled -- crash */

to 

   if (access fixup) remember we've done something
   handle MMIO
   ...
   if (we did a fixup above)
     return 1  /* try again */
   else
     return 0  /* crash */

does what you want without making the handler much bigger and more
brittle. 

Tim.

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