Re: [Xen-devel] [PATCH v4 08/16] xen/mm: Drop the parameter mfn from populate_pt_range

[Julien Grall <julien.grall@xxxxxxx>]

Hi Wei,

On 22/02/18 16:35, Wei Liu wrote:
> On Wed, Feb 21, 2018 at 02:02:51PM +0000, Julien Grall wrote:
> > The function populate_pt_range is used to populate in advance the
> > page-table but it will not do the actual mapping. So passing the MFN in
> > parameter is pointless. Note that the only caller pass 0...
> >
> > At the same time replace 0 by INVALID_MFN to make clear the MFN is
> > invalid.
> The mfn parameter is the first mfn of a consecutive nr MFNs passed to
> map_pages_to_xen. Putting INVALID_MFN isn't helping -- the value written
> to page table(s) will wrap around to 0.
>
> And I think starting from 0 to avoid overflow is probably a better
> behaviour. If you really want to make sure all entries are filled with
> INVALID_MFN you should call map_pages_to_xen for nr times with each
> page.
I am not sure to understand this. From its name, populate_pt_range 
should only create the intermediate tables. The leaf entry will stay 
invalid. So how the value of mfn matters? Is it because the code is 
written in a such way that passing INVALID_MFN will result to undefined 
behavior?
Cheers,

--
Julien Grall

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