linux-kernel - Re: [PATCH v6 04/14] mm, hugetlbfs: Allow for "high" userspace addresses

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Message-ID: <YdR0EN2mdJuysugk@arm.com>
Date:   Tue, 4 Jan 2022 16:21:36 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "alex@...ti.fr" <alex@...ti.fr>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "will@...nel.org" <will@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Steve Capper <steve.capper@....com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v6 04/14] mm, hugetlbfs: Allow for "high" userspace
 addresses

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 <christophe.leroy@...roup.eu>
> Cc: Steve Capper <steve.capper@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Catalin Marinas <catalin.marinas@....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: <stable@...r.kernel.org> # 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@....com>