From: Wei Liu <wei.liu2@xxxxxxxxxx>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit 09ed3d5ba06137913960f9c9385f71fc384193ab upstream.
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@xxxxxxxxxx>
Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
drivers/xen/balloon.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index b232908a6192..4c437efa9d91 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -405,11 +405,25 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
state = BP_EAGAIN;
break;
}
+ scrub_page(page);
- pfn = page_to_pfn(page);
- frame_list[i] = pfn_to_mfn(pfn);
+ frame_list[i] = page_to_pfn(page);
+ }
- scrub_page(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);
/*
* Ballooned out frames are effectively replaced with
@@ -433,11 +447,9 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
}
put_balloon_scratch_page();
- 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);
--
1.9.1
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