On Fri, Dec 17, 2021 at 10:27:28AM +0000, Christophe Leroy wrote:

This is a complement of f6795053dac8 ("mm: mmap: Allow for "high"
userspace addresses") for hugetlb.

This patch adds support for "high" userspace addresses that are
optionally supported on the system and have to be requested via a hint
mechanism ("high" addr parameter to mmap).

Architectures such as powerpc and x86 achieve this by making changes to
their architectural versions of hugetlb_get_unmapped_area() function.
However, arm64 uses the generic version of that function.

So take into account arch_get_mmap_base() and arch_get_mmap_end() in
hugetlb_get_unmapped_area(). To allow that, move those two macros
out of mm/mmap.c into include/linux/sched/mm.h

If these macros are not defined in architectural code then they default
to (TASK_SIZE) and (base) so should not introduce any behavioural
changes to architectures that do not define them.

For the time being, only ARM64 is affected by this change.

Signed-off-by: Christophe Leroy <redacted>
Cc: Steve Capper <redacted>
Cc: Will Deacon <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
---
 fs/hugetlbfs/inode.c     | 9 +++++----
 include/linux/sched/mm.h | 8 ++++++++
 mm/mmap.c                | 8 --------
 3 files changed, 13 insertions(+), 12 deletions(-)

This would be an ABI change but I'm fine with it. Basically with this
patch, getting hugetblfs addresses above 48-bit require explicit hint
passed to mmap().

I wonder whether we should add a fixes tag (or at least the cc stable):

Fixes: f6795053dac8 ("mm: mmap: Allow for "high" userspace addresses")
Cc: <redacted> # 5.0.x

I think the original commit should have changed
hugetlb_get_unmapped_area() to have the same behaviour as
arch_get_unmapped_area(). Steve, any thoughts?

FWIW,

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>