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

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: f4ea6dcb08 ("powerpc/mm: Enable mappings above 128TB")
Cc: stable@vger.kernel.org # v4.12+
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>
This commit is contained in:
Nicholas Piggin 2017-11-10 04:27:37 +11:00 committed by Michael Ellerman
parent 6a72dc038b
commit effc1b2508
1 changed files with 4 additions and 4 deletions
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8
arch/powerpc/mm/mmu_context_book3s64.c
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@ -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