[Xen-devel] [PATCH for-4.8] altp2m: don't attempt to unshare pages during change_altp2m_gfn op

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

Attempting to change gfn mappings with altp2m on a memory shared page results
in a lock-order violation (mm locking order violation: 282 > 254), which
crashes the hypervisor. Don't attempt to automatically unshare such pages and
just fall back to failing the op if the page type is not correct.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/mm/p2m.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 9526fff..6a45185 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -2628,7 +2628,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned int 
idx,
     if ( !mfn_valid(mfn) )
     {
         mfn = __get_gfn_type_access(hp2m, gfn_x(old_gfn), &t, &a,
-                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 0);
+                                    P2M_ALLOC, &page_order, 0);
 
         if ( !mfn_valid(mfn) || t != p2m_ram_rw )
             goto out;
-- 
2.9.3


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