xen/balloon: flush persistent kmaps in correct position
Xen balloon driver will update ballooned out pages' P2M entries to point to scratch page for PV guests. In 24f69373 ("xen/balloon: don't alloc page while non-preemptible", kmap_flush_unused was moved after updating P2M table. In that case for 32 bit PV guest we might end up with P2M X -----> S (S is mfn of balloon scratch page) M2P Y -----> X (Y is mfn in persistent kmap entry) kmap_flush_unused() iterates through all the PTEs in the kmap address space, using pte_to_page() to obtain the page. If the p2m and the m2p are inconsistent the incorrect page is returned. This will clear page->address on the wrong page which may cause subsequent oopses if that page is currently kmap'ed. Move the flush back between get_page and __set_phys_to_machine to fix this. Signed-off-by: Wei Liu <wei.liu2@citrix.com> Signed-off-by: David Vrabel <david.vrabel@citrix.com> Cc: stable@vger.kernel.org # 3.12+
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