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Subject[PATCH 4.14 170/193] powerpc/64s/hash: Fix fork() with 512TB process address space
4.14-stable review patch.  If anyone has any objections, please let me know.


From: Nicholas Piggin <>

commit effc1b25088502fbd30305c79773de2d1f7470a6 upstream.

Hash unconditionally resets the addr_limit to default (128TB) when the
mm context is initialised. If a process has > 128TB mappings when it
forks, the child will not get the 512TB addr_limit, so accesses to
valid > 128TB mappings will fail in the child.

Fix this by only resetting the addr_limit to default if it was 0. Non
zero indicates it was duplicated from the parent (0 means exec()).

Fixes: f4ea6dcb08ea ("powerpc/mm: Enable mappings above 128TB")
Signed-off-by: Nicholas Piggin <>
Reviewed-by: Aneesh Kumar K.V <>
Signed-off-by: Michael Ellerman <>
Signed-off-by: Greg Kroah-Hartman <>

arch/powerpc/mm/mmu_context_book3s64.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/arch/powerpc/mm/mmu_context_book3s64.c
+++ b/arch/powerpc/mm/mmu_context_book3s64.c
@@ -93,11 +93,11 @@ static int hash__init_new_context(struct
return index;

- * We do switch_slb() early in fork, even before we setup the
- * mm->context.addr_limit. Default to max task size so that we copy the
- * default values to paca which will help us to handle slb miss early.
+ * In the case of exec, use the default limit,
+ * otherwise inherit it from the mm we are duplicating.
- mm->context.addr_limit = DEFAULT_MAP_WINDOW_USER64;
+ if (!mm->context.addr_limit)
+ mm->context.addr_limit = DEFAULT_MAP_WINDOW_USER64;

* The old code would re-promote on fork, we don't do that when using

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