Re: [Xen-devel] [PATCH v6] x86/altp2m: Aggregate get entry and populate into common funcs

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Tue, Apr 23, 2019 at 8:30 AM Alexandru Stefan ISAILA
<aisaila@xxxxxxxxxxxxxxx> wrote:
>
> The code for getting the entry and then populating was repeated in
> p2m_change_altp2m_gfn() and in p2m_set_altp2m_mem_access().
>
> The code is now in one place with a bool param that lets the caller choose
> if it populates after get_entry().
>
> If remapping is being done then both the old and new gfn's should be
> unshared in the hostp2m for keeping things consistent. The page type
> of old_gfn was already checked whether it's p2m_ram_rw and bail if it
> wasn't so functionality-wise this just simplifies things as a user
> doesn't have to request unsharing manually before remapping.
> Now, if the new_gfn is invalid it shouldn't query the hostp2m as
> that is effectively a request to remove the entry from the altp2m.
> But provided that scenario is used only when removing entries that
> were previously remapped/copied to the altp2m, those entries already
> went through P2M_ALLOC | P2M_UNSHARE before, so it won't have an
> affect so the core function get_altp2m_entry() is calling
> __get_gfn_type_access() with P2M_ALLOC | P2M_UNSHARE.
>
> altp2m_get_entry_direct() is also called in p2m_set_suppress_ve()
> because on a new altp2m view the function will fail with invalid mfn if
> p2m->set_entry() was not called before.
>
> Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>

Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>

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