Re: [PATCH V2 2/7] xen/grants: support allocating consecutive grants

[Oleksandr <olekstysh@xxxxxxxxx>]

On 12.05.22 00:09, Boris Ostrovsky wrote:


Hello Boris


> On 5/11/22 2:00 PM, Oleksandr wrote:
> > On 07.05.22 21:19, Oleksandr Tyshchenko wrote:
> >
> > Hello Boris, Stefano
> >
> >
> > > From: Juergen Gross <jgross@xxxxxxxx>
> > >
> > > For support of virtio via grant mappings in rare cases larger mappings
> > > using consecutive grants are needed. Support those by adding a bitmap
> > > of free grants.
> > >
> > > As consecutive grants will be needed only in very rare cases (e.g. when
> > > configuring a virtio device with a multi-page ring), optimize for the
> > > normal case of non-consecutive allocations.
> > >
> > > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > > ---
> > > Changes RFC -> V1:
> > >     - no changes
> > >     Changes V1 -> V2:
> > >     - no changes
> >
> > May I please ask for the review here?
>
>
> I had a quick look but I am stuck on get_free_seq(), I need to stare 
> at it some more. Unless someone else reviews this, I will try to get 
> to this in the next couple of days.

Thank you!


> One thing I did notice is
>
>
> > > @@ -1452,6 +1624,13 @@ int gnttab_init(void)
> > >           }
> > >       }
> > >   +    i = gnttab_interface->grefs_per_grant_frame * 
> > > max_nr_grant_frames;
> > > +    gnttab_free_bitmap = bitmap_zalloc(i, GFP_KERNEL);
> > > +    if (!gnttab_free_bitmap) {
> > > +        ret = -ENOMEM;
> > > +        goto ini_nomem;
> > > +    }
>
> This overwrites 'i' and will break error handling at ini_nomem.

Indeed, will fix. Thank you for pointing this out.


> -boris
--
Regards,

Oleksandr Tyshchenko