Re: [Xen-devel] [RFC 20/22] xen/arm: p2m: Re-implement p2m_insert_mapping using p2m_set_entry

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 06/09/2016 19:57, Stefano Stabellini wrote:
> On Thu, 28 Jul 2016, Julien Grall wrote:
> > The function p2m_insert_mapping can be re-implemented using the generic
> > function p2m_set_entry.
> >
> > Note that the mapping is not reverted anymore if Xen fails to insert a
> > mapping. This was added to ensure the MMIO are not kept half-mapped
> > in case of failure and to follow the x86 counterpart. This was removed
> > on the x86 part by commit c3c756bd "x86/p2m: use large pages for MMIO
> > mappings" and I think we should let the caller taking care of it.
> >
> > Finally drop the operation INSERT in apply_* as nobody is using it
> > anymore. Note that the functios could have been dropped in one go at the
>                            ^ functions
>
> > end, however I find easier to drop the operations one by one avoiding a
> > big deletion in the patch that convert the last operation.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> >
> > ---
> >     Whilst there is no safety checks on what is replaced in the P2M
> >     (such as foreign/grant mapping as x86 does), we may want to add it
> >     ensuring the guest is not doing something dumb. Any opinions?
> We don't necessarily need to protect a guest from its own dumbness, as
> long as we can correctly deal with it (account for grant and foreign
> mappings replaced this way).
I think this could be a good improvement for the future and help 
debugging potential bug in the guest.
Anyway, it is not strictly necessary today given that all the reference 
counting should be done properly. I will add it in my todo list.
> Given that the old code doesn't do it anyway:
>
> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Thank you!

Regards,

--
Julien Grall

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