Re: [PATCH] mm: hugetlb: Add missing cache flushing in hugetlb_unshare_all_pmds()

[Muchun Song <songmuchun@bytedance.com>]

On Sun, Apr 24, 2022 at 02:33:19PM +0800, Baolin Wang wrote:
> Missed calling flush_cache_range() before removing the sharing PMD entrires,
> otherwise data consistence issue may be occurred on some architectures whose
> caches are strict and require a virtual–>physical translation to exist for
> a virtual address. Thus add it.
> 
> Fixes: 6dfeaff93be1 ("hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp")
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>

CONFIG_ARCH_WANT_HUGE_PMD_SHARE is only definded on riscv, arm64 and
x86.  All of them do not have a VIVT cache.  In others words,
flush_cache_range() is null on those architectures. So I suspect
in practice this does not cause any issue.  It is better to
clarify this in commit log.

Anyway:

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.