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Subject[ 012/108] xen/setup: Fix one-off error when adding for-balloon PFNs to the P2M.
From: Greg KH <>

3.5-stable review patch. If anyone has any objections, please let me know.


From: Konrad Rzeszutek Wilk <>

commit c96aae1f7f393387d160211f60398d58463a7e65 upstream.

When we are finished with return PFNs to the hypervisor, then
populate it back, and also mark the E820 MMIO and E820 gaps
as IDENTITY_FRAMEs, we then call P2M to set areas that can
be used for ballooning. We were off by one, and ended up
over-writting a P2M entry that most likely was an IDENTITY_FRAME.
For example:

1-1 mapping on 40000->40200
1-1 mapping on bc558->bc5ac
1-1 mapping on bc5b4->bc8c5
1-1 mapping on bc8c6->bcb7c
1-1 mapping on bcd00->100000
Released 614 pages of unused memory
Set 277889 page(s) to 1-1 mapping
Populating 40200-40466 pfn range: 614 pages added

=> here we set from 40466 up to bc559 P2M tree to be
INVALID_P2M_ENTRY. We should have done it up to bc558.

The end result is that if anybody is trying to construct
a PTE for PFN bc558 they end up with ~PAGE_PRESENT.

Reported-by-and-Tested-by: Andre Przywara <>
Signed-off-by: Konrad Rzeszutek Wilk <>
Signed-off-by: Greg Kroah-Hartman <>

arch/x86/xen/setup.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -78,9 +78,16 @@ static void __init xen_add_extra_mem(u64
memblock_reserve(start, size);

xen_max_p2m_pfn = PFN_DOWN(start + size);
+ for (pfn = PFN_DOWN(start); pfn < xen_max_p2m_pfn; pfn++) {
+ unsigned long mfn = pfn_to_mfn(pfn);
+ if (WARN(mfn == pfn, "Trying to over-write 1-1 mapping (pfn: %lx)\n", pfn))
+ continue;
+ WARN(mfn != INVALID_P2M_ENTRY, "Trying to remove %lx which has %lx mfn!\n",
+ pfn, mfn);

- for (pfn = PFN_DOWN(start); pfn <= xen_max_p2m_pfn; pfn++)
__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+ }

static unsigned long __init xen_do_chunk(unsigned long start,

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