Re: [Xen-devel] [PATCH] EPT: refine epte_present test

[Tim Deegan <tim@xxxxxxx>]

At 04:58 -0800 on 19 Jan (1326949088), Andres Lagar-Cavilla wrote:
> > Hi,
> >
> > I agree with the idea of this patch but:
> >
> >> +static inline bool_t is_epte_valid(ept_entry_t *e)
> >> +{
> >> +    ept_entry_t rights = { .epte = 0 };
> >> +
> >> +    /* Not valid if empty */
> >> +    if (e->epte == 0) return 0;
> >> +
> >> +    /* Not valid if mfn not valid */
> >> +    if ( !mfn_valid(e->mfn) ) return 0;
> >> +
> >> +    /* Not valid if rights different from those of
> >> +     * its p2m type and access combination */
> >> +    ept_p2m_type_to_flags(&rights, e->sa_p2mt, e->access);
> >> +    if ( epte_permissions(&rights) != epte_permissions(e) )
> >> +        return 0;
> >
> > This is a rather odd set of tests.  Since we construct EPT pagetables
> > ourselves, I think that we only need to test for uninitialised entries
> > and explicitly invalid entries.
> >
> > Does this patch work for you?
> 
> It will achieve the stated goal. I am curious as to whether we should
> check for p2m_broken. In any case:
> Acked-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>

Thanks.  I've committed the patch as-is; I think in the current code
p2m_ram_broken doesn't need a special case.

Cheers,

Tim.

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