Re: [Xen-devel] [PATCHv4 04/14] xen: remove scratch frames for ballooned pages and m2p override

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 27 Jan 2015, David Vrabel wrote:
> On 27/01/15 10:57, Stefano Stabellini wrote:
> > On Mon, 26 Jan 2015, David Vrabel wrote:
> >> The scratch frame mappings for ballooned pages and the m2p override
> >> are broken.  Remove them in preparation for replacing them with
> >> simpler mechanisms that works.
> >>
> >> The scratch pages did not ensure that the page was not in use.  In
> >> particular, the foreign page could still be in use by hardware.  If
> >> the guest reused the frame the hardware could read or write that
> >> frame.
> >>
> >> The m2p override did not handle the same frame being granted by two
> >> different grant references.  Trying an M2P override lookup in this
> >> case is impossible.
> >>
> >> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> > 
> > [...]
> > 
> >>  int set_foreign_p2m_mapping(struct gnttab_map_grant_ref *map_ops,
> >>                        struct gnttab_map_grant_ref *kmap_ops,
> >>                        struct page **pages, unsigned int count)
> >>  {
> >>    int i, ret = 0;
> >> -  bool lazy = false;
> >>    pte_t *pte;
> >>  
> >>    if (xen_feature(XENFEAT_auto_translated_physmap))
> >>            return 0;
> >>  
> >> -  if (kmap_ops &&
> >> -      !in_interrupt() &&
> >> -      paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
> >> -          arch_enter_lazy_mmu_mode();
> >> -          lazy = true;
> >> +  if (kmap_ops) {
> >> +          ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
> >> +                                          kmap_ops, count);
> >> +          if (ret)
> >> +                  goto out;
> >>    }
> > 
> > I think that you should explain why you are adding one more grant table
> > mapping to a function meant to work on the p2m/m2p.  Everything else is
> > clear.
> 
> I'm not.  This function has always done this.

Can you be more specific please?

I cannot see a call to HYPERVISOR_grant_table_op among the lines you are
removing from this function in this patch.

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