linux-kernel - Re: [PATCH] mm/hugetlb: correct demote page offset logic

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Date:   Thu, 15 Sep 2022 08:19:22 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        Doug Berger <opendmb@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Muchun Song <songmuchun@...edance.com>,
        Oscar Salvador <osalvador@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: correct demote page offset logic



On 9/15/22 02:48, Mike Kravetz wrote:
> On 09/14/22 12:09, Doug Berger wrote:
>> With gigantic pages it may not be true that struct page structures
>> are contiguous across the entire gigantic page. The nth_page macro
>> is used here in place of direct pointer arithmetic to correct for
>> this.
>>
>> Fixes: 8531fc6f52f5 ("hugetlb: add hugetlb demote page support")
>> Signed-off-by: Doug Berger <opendmb@...il.com>
>> Cc: <stable@...r.kernel.org>
>> ---
>>  mm/hugetlb.c | 14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> Thanks!
> 
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
> 
> To answer Andrew's question about user-visible runtime effects.
> We could get addressing exceptions.  However, this is only possible in
> configurations where CONFIG_SPARSEMEM && !CONFIG_SPARSEMEM_VMEMMAP.
> Such a configuration option is rare an unknown to be the default
> anywhere.

In that case, should this be a 'Cc: stable' ? Although it does fix
the above mentioned commit for a possible configuration. But should
this be backported, if there could not have been an affected system ?