Re: [Xen-devel] [PATCH v2] xen/arm: p2m: Correctly flush TLB in create_p2m_entries

[Tim Deegan <tim@xxxxxxx>]

At 15:28 +0000 on 14 Jan (1389709716), Ian Campbell wrote:
> On Thu, 2014-01-09 at 16:34 +0000, Julien Grall wrote:
> > Except grant-table (I can't find {get,put}_page for grant-table code???),
> 
> I think they are in __gnttab_map_grant_ref, within __get_paged_frame or
> through page_get_owner_and_reference.
> 
> and on unmap it is in__gnttab_unmap_common_complete.
> 
> It's a bit of a complex maze though so I'm not entirely sure, perhaps
> Tim, Keir or Jan can confirm that a grant mapping always takes a
> reference on the mapped page (it seems like PV x86 ought to be relying
> on this for safety anyhow).

Not claiming to understand it completely, but I agree with your analysis.

> I think the flush in alloc_heap_pages would also serve as a backstop,
> wouldn't it?

Not entirely -- if the grant mapping didn't take a ref, then the page
could be freed and reassigned with the grant mapping still in place --
the TLB flush doesn't help if the PTE is still there. :)

Cheers,

Tim.

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