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xen/balloon: flush persistent kmaps in correct position

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Xen balloon driver will update ballooned out pages' P2M entries to point
to scratch page for PV guests. In 24f69373e2 ("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+
This commit is contained in:
Wei Liu 2014-03-15 16:11:47 +00:00 committed by David Vrabel
parent b098d6726b
commit 09ed3d5ba0
1 changed files with 19 additions and 7 deletions
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26
drivers/xen/balloon.c
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@ -399,12 +399,26 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
state = BP_EAGAIN;
break;
}
pfn = page_to_pfn(page);
frame_list[i] = pfn_to_mfn(pfn);
scrub_page(page);
frame_list[i] = page_to_pfn(page);
}
/*
* Ensure that ballooned highmem pages don't have kmaps.
*
* Do this before changing the p2m as kmap_flush_unused()
* reads PTEs to obtain pages (and hence needs the original
* p2m entry).
*/
kmap_flush_unused();
/* Update direct mapping, invalidate P2M, and add to balloon. */
for (i = 0; i < nr_pages; i++) {
pfn = frame_list[i];
frame_list[i] = pfn_to_mfn(pfn);
page = pfn_to_page(pfn);
#ifdef CONFIG_XEN_HAVE_PVMMU
/*
* Ballooned out frames are effectively replaced with
@ -429,11 +443,9 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
}
#endif
balloon_append(pfn_to_page(pfn));
balloon_append(page);
}
/* Ensure that ballooned highmem pages don't have kmaps. */
kmap_flush_unused();
flush_tlb_all();
set_xen_guest_handle(reservation.extent_start, frame_list);