powerpc/64s/hash: Fix fork() with 512TB process address space

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 <npiggin@gmail.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
index 05e15386d4cb356da7e5b320be4b92907c99500b..b94fb62e60fde96936e4a2d62f43c22b809437eb 100644 (file)
--- 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 mm_struct *mm)
                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