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SubjectRe: [PATCH v10] mm, hugetlbfs: Allow for "high" userspace addresses
Hi Catalin,

Le 16/04/2022 à 00:09, Andrew Morton a écrit :
> On Fri, 15 Apr 2022 16:45:13 +0200 Christophe Leroy <> wrote:
>> This is a fix for commit 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.
>> >From Catalin (ARM64):
>> We should have fixed hugetlb_get_unmapped_area() as well when we
>> added support for 52-bit VA. The reason for commit f6795053dac8 was to
>> prevent normal mmap() from returning addresses above 48-bit by default
>> as some user-space had hard assumptions about this.
>> It's a slight ABI change if you do this for hugetlb_get_unmapped_area()
>> but I doubt anyone would notice. It's more likely that the current
>> behaviour would cause issues, so I'd rather have them consistent.
> I'm struggling to understand the need for a -stable backport from the
> above text.
> Could we please get a simple statement of the end-user visible effects
> of the shortcoming? Target audience is -stable tree maintainers, and
> people who we've never heard of who will be wondering whether they should
> add this to their organization's older kernel.

Catalin, can you help answering this question ? It was your
recommendation to tag this patch for stable in

>> fs/hugetlbfs/inode.c | 9 +++++----
>> include/linux/sched/mm.h | 8 ++++++++
>> mm/mmap.c | 8 --------
>> 3 files changed, 13 insertions(+), 12 deletions(-)
> I'm a bit surprised that this has reached version 10! Was it really
> that tricky?

Well, that's the series it was part of that has reached v10. This patch
was introduced in the series in v6


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