linux-kernel - Re: [PATCH 2/3] mm/mprotect: Use long for page accountings and retval

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Date:   Thu, 5 Jan 2023 01:51:19 +0000
From:   James Houghton <jthoughton@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/3] mm/mprotect: Use long for page accountings and retval

On Wed, Jan 4, 2023 at 10:52 PM Peter Xu <peterx@...hat.com> wrote:
>
> Switch to use type "long" for page accountings and retval across the whole
> procedure of change_protection().
>
> The change should have shrinked the possible maximum page number to be half
> comparing to previous (ULONG_MAX / 2), but it shouldn't overflow on any
> system either because the maximum possible pages touched by change
> protection should be ULONG_MAX / PAGE_SIZE.
>
> Two reasons to switch from "unsigned long" to "long":
>
>   1. It suites better on count_vm_numa_events(), whose 2nd parameter takes
>      a long type.
>
>   2. It paves way for returning negative (error) values in the future.
>
> Currently the only caller that consumes this retval is change_prot_numa(),
> where the unsigned long was converted to an int.  Since at it, touching up
> the numa code to also take a long, so it'll avoid any possible overflow too
> during the int-size convertion.
>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  include/linux/hugetlb.h |  4 ++--
>  include/linux/mm.h      |  2 +-
>  mm/hugetlb.c            |  4 ++--
>  mm/mempolicy.c          |  2 +-
>  mm/mprotect.c           | 26 +++++++++++++-------------
>  5 files changed, 19 insertions(+), 19 deletions(-)

Acked-by: James Houghton <jthoughton@...gle.com>