Re: [Xen-devel] Live migration with MMIO pages

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 31/10/07 16:34, "Kieran Mansley" <kmansley@xxxxxxxxxxxxxx> wrote:

> Yes.  The reason it's failing is that sh_page_fault() in
> xen/arch/x86/mm/shadow/multi.c thinks it's a bad gfn:
> 
>     if ( !p2m_is_valid(p2mt) || (!(p2m_is_mmio(p2mt) || mfn_valid
> (gmfn))) )
>     {
>         perfc_incr(shadow_fault_bail_bad_gfn);
>         SHADOW_PRINTK("BAD gfn=%"SH_PRI_gfn" gmfn=%"PRI_mfn"\n",
>                       gfn_x(gfn), mfn_x(gmfn));
>         goto not_a_shadow_fault;
>     }
> 
> I think the problem is that set_mmio_p2m_entry() isn't getting called
> when the IO mapping is established.  There are three places where
> iomem_permit_access() is called:

No, basically that pagefault-handler check is nonsense for a PV guest. We
don't have a p2m table in Xen for PV guests because they are not 'translated
mode'. So there is nowhere for us to store the 'mmio' p2m type.

Perhaps Tim has a good idea what to do here. Adding a
!shadow_mode_translate() condition to the if statement would probably work
but I'm not sure it's the neatest answer.

 -- Keir



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