Re: [Xen-devel] [PATCH v2 07/25] arm/altp2m: Add altp2m init/teardown routines.

[Julien Grall <julien.grall@xxxxxxx>]

On 05/08/16 07:53, Sergej Proskurin wrote:
> Hi Julien,
Hello Sergej,

> On 08/03/2016 08:12 PM, Julien Grall wrote:
> > On 01/08/16 18:10, Sergej Proskurin wrote:
> > > +int altp2m_init(struct domain *d)
> > > +{
> > > +    unsigned int i;
> > > +
> > > +    spin_lock_init(&d->arch.altp2m_lock);
> > > +
> > > +    for ( i = 0; i < MAX_ALTP2M; i++ )
> > > +    {
> > > +        d->arch.altp2m_p2m[i] = NULL;
> > > +        d->arch.altp2m_vttbr[i] = INVALID_VTTBR;
> > I don't think altp2m_vttbr is useful. There is no real performance
> > impact to free the whole altp2m if the altp2m is destroyed (see
> > altp2m_destroy_by_id) and re-allocated afterwards.
> >
> > The code will actually much simpler. With this solution you will be
> > able to detect if an altp2m is available by testin altp2m_p2m[i] is NULL.
> This is true. I did not want to free the entire domain got every time
> the hostp2m got changed, while altp2m was active (see
> altp2m_propagate_change). But it would not introduce much more overhead
> when it does. Thank you.
I think you misunderstood my point. When you flush the altp2m you only 
need to reset lowest_mapped_gfn and max_mapped_gfn aside freeing 
intermediate page table.
The altp2m should be fully freed when it get destroyed, nobody will use 
it anyway. This will also simplify a lot the logic.
Regards,

--
Julien Grall

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