Re: [PATCH v10 01/19] KVM: s390: pv: leak the topmost page table when destroy fails

[Claudio Imbrenda]

On Mon, 16 May 2022 09:22:09 +0200
Nico Boehr <nrb@xxxxxxxxxxxxx> wrote:

> On Thu, 2022-04-14 at 10:02 +0200, Claudio Imbrenda wrote:
> 
> [...]
> > +/**
> > + * s390_replace_asce - Try to replace the current ASCE of a gmap
> > with
> > + * another equivalent one.
> > + * @gmap the gmap
> > + *
> > + * If the allocation of the new top level page table fails, the ASCE
> > is not
> > + * replaced.
> > + * In any case, the old ASCE is always removed from the list.
> > Therefore the
> > + * caller has to make sure to save a pointer to it beforehands,
> > unless an
> > + * intentional leak is intended.
> > + */
> > +int s390_replace_asce(struct gmap *gmap)
> > +{
> >   
> [...]
> > +       /* Set new table origin while preserving existing ASCE
> > control bits */
> > +       asce = (gmap->asce & ~_ASCE_ORIGIN) | __pa(table);
> > +       WRITE_ONCE(gmap->asce, asce);  
> 
> Can someone concurrently touch the control bits?

should not happen, nobody is using the ASCE while we replace it

moreover, all callers of s390_replace_asce hold kvm->lock, as do all
functions changing the ASCE