Re: [Xen-devel] [PATCH 11/18] arm/altp2m: Make flush_tlb_domain ready for altp2m.

[Julien Grall <julien.grall@xxxxxxx>]

On 05/07/16 21:21, Sergej Proskurin wrote:
> On 07/05/2016 05:37 PM, Julien Grall wrote:
> > > When altp2m is active, the hostp2m is not used. All changes are applied
> > > directly to the individual altp2m views. As far as I know, the only
> > > situations, where a mapping is removed from a specific p2m view is in
> > > the functions unmap_regions_rw_cache, unmap_mmio_regions, and
> > > guest_physmap_remove_page. Each one of these functions provide, however
> > > the hostp2m to the function apply_p2m_changes, where the mapping is
> > > eventually removed. So, we definitely remove mappings from the hostp2m.
> > > However, these would not be removed from the associated altp2m views.
> > >
> > > Can you state a scenario, when and why pages might need to be removed at
> > > run time from the hostp2m? In that case, maybe it would make sense to
> > > extend the three functions (unmap_regions_rw_cache, unmap_mmio_regions,
> > > and guest_physmap_remove_page) to additionally remove the mappings from
> > > all available altp2m views?
> > All the functions, you mentioned can be called after the domain has been
> > created. If you grep guest_physmap_remove_page in the code source, you
> > will find that it is used to unmap grant entry from the memory (see
> > replace_grant_host_mapping) or when decreasing the memory reservation
> > (see do_memory_op).
> >
> > Note that, from my understanding, x86 has the same problem.
> Yes, the x86 implementation works similarly to the one for ARM. I will
> need to think about that. One solution could simply extend the
> previously mentioned functions by unmapping the particular entry in all
> currently available altp2m views (assuming, we allocate the altp2m views
> on demand, as discussed in patch #05).
>
> Whatever the solution will be, it will need to be ported to the x86
> implementation as well.
Actually, the x86 code is propagating the change (see 
p2m_altp2m_propagate_change). I missed it while going the code the first 
time.
Cheers,

--
Julien Grall

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