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

[Doug Berger]

On 9/14/2022 1:49 PM, Andrew Morton wrote:
> On Wed, 14 Sep 2022 12:09:17 -0700 Doug Berger <opendmb@xxxxxxxxx> 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.
>
> What were the user-visible runtime effects of this bug?
As Mike said this would only conceptually be a problem for systems with 
CONFIG_SPARSEMEM && !CONFIG_SPARSEMEM_VMEMMAP, and could cause kernel 
address exceptions or memory corruption with unpredictable side effects.

However, I am unaware of a system other than perhaps the PS3 that uses 
the classic sparse addressing, so the odds of such a system also using 
gigantic hugetlbfs pages that it wants to demote is likely quite small.

Thanks,
-Doug