Nicholas Piggin <npig...@gmail.com> writes:
> 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()).
>
Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
> Cc: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
> Fixes: f4ea6dcb08 ("powerpc/mm: Enable mappings above 128TB")
> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
> ---
> arch/powerpc/mm/mmu_context_book3s64.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/mm/mmu_context_book3s64.c
> b/arch/powerpc/mm/mmu_context_book3s64.c
> index 6d724dab27c2..846cbad45fce 100644
> --- 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
> --
> 2.15.0
