Re: [Xen-devel] [PATCH for-4.13] xen/arm: mm: Allow generic xen page-tables helpers to be called early

[Julien Grall <julien.grall@xxxxxxx>]

(+ Andrew and Jan)

Hi,

On 11/10/2019 01:27, Stefano Stabellini wrote:
> On Thu, 10 Oct 2019, Julien Grall wrote:
> > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> > index be23acfe26..a6637ce347 100644
> > --- a/xen/arch/arm/mm.c
> > +++ b/xen/arch/arm/mm.c
> > @@ -964,11 +964,40 @@ static int create_xen_table(lpae_t *entry)
> >   
> >   static lpae_t *xen_map_table(mfn_t mfn)
> >   {
> > +    /*
> > +     * We may require to map the page table before map_domain_page() is
> > +     * useable. The requirements here is it must be useable as soon as
> > +     * page-tables are allocated dynamically via alloc_boot_pages().
> > +     *
> > +     * We need to do the check on physical address rather than virtual
> > +     * address to avoid truncation on Arm32. Therefore is_kernel() cannot
> > +     * be used.
> > +     */
> > +    if ( system_state == SYS_STATE_early_boot )
> > +    {
> > +        const mfn_t mstart = virt_to_mfn(_start);
> > +        const mfn_t mend = virt_to_mfn(_end);
> > +
> > +        if ( (mfn_x(mstart) <= mfn_x(mfn)) && (mfn_x(mfn) < mfn_x(mend)) )
> > +        {
> The patch is good. Actually I noticed that we already have
> is_xen_fixed_mfn(), looks like it is made for this. I think we should
> use it here, except that is_xen_fixed_mfn has:
Thanks, I thought we had one but I couldn't remember the name :(.

>       (mfn_to_maddr(mfn) <= virt_to_maddr(&_end)))
>
> I think it should actually be:
>
>       (mfn_to_maddr(mfn) < virt_to_maddr(&_end)))
>
> Maybe we could fix that at the same time in one patch? However, it is
> the same definition as on x86, so I don't know what is going on there.
For Arm we should definitely use < and not <=.

I am assuming this is the same for x86. Andrew? Jan?

Cheers,

--
Julien Grall

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