Re: [Xen-devel] [PATCH V2 3/3] xen: eliminate scalability issues from initial mapping setup

[Juergen Gross]

On 09/17/2014 04:42 PM, David Vrabel wrote:
> On 17/09/14 15:20, Juergen Gross wrote:
> > On 09/17/2014 04:07 PM, David Vrabel wrote:
> > > Are you missing a ClearPagePinned(..) here?
> >
> > Probably, yes.
>
> Jan pointed out that this is not needed.
>
> > > > @@ -1529,6 +1604,22 @@ static pte_t __init mask_rw_pte(pte_t *ptep,
> > > > pte_t pte)
> > > >    #else /* CONFIG_X86_64 */
> > > >    static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte)
> > > >    {
> > > > +    unsigned long pfn;
> > > > +
> > > > +    if (xen_feature(XENFEAT_writable_page_tables) ||
> > > > +        xen_feature(XENFEAT_auto_translated_physmap) ||
> > > > +        xen_start_info->mfn_list >= __START_KERNEL_map)
> > > > +        return pte;
> > > > +
> > > > +    /*
> > > > +     * Pages belonging to the initial p2m list mapped outside the
> > > > default
> > > > +     * address range must be mapped read-only.
> > >
> > > Why?  I didn't think was anything special about these MFNs.
> >
> > The hypervisor complained when I did otherwise. I think the main reason
> > is that the hypervisor will set up some more page tables to be able to
> > map then mfn_list outside the "normal" address range. They are located
> > in the range starting at xen_start_info->first_p2m_pfn (otherwise the
> > info in first_p2m_pfn and nr_p2m_frames wouldn't be needed).
>
> Ok. Can you expand the comment to say this?

Already did. :-)


Juergen
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