Re: [PATCH v2] mm: Track page table modifications in __apply_to_page_range()

[Andrew Morton]

On Fri, 21 Aug 2020 14:37:46 +0200 Joerg Roedel <joro@xxxxxxxxxx> wrote:

> The __apply_to_page_range() function is also used to change and/or
> allocate page-table pages in the vmalloc area of the address space.
> Make sure these changes get synchronized to other page-tables in the
> system by calling arch_sync_kernel_mappings() when necessary.

There's no description here of the user-visible effects of the bug. 
Please always provide this, especially when proposing a -stable
backport.  Take pity upon all the downstream kernel maintainers who are
staring at this wondering whether they should risk adding it to their
kernels.