Re: [PATCH v3 21/40] mm/gup: error out early on !VMA_MAYREAD_BIT VMAs

[Zi Yan]

On Thu Sep 17, 2026 at 12:22 PM EDT, Lorenzo Stoakes (ARM) wrote:
> When populating a VMA range via the aptly named populate_vma_page_range()
> an unreadable VMA will always eventually fail with -EFAULT.
>
> That a VMA is accessible is always checked, however VMA_MAYREAD_BIT is not.
>
> All user mappings always have VMA_MAYREAD_BIT set, so this check only
> impacts kernel mappings.
>
> It is implemented specifically to disallow population of uprobes XOL
> mappings which are exec-only.
>
> A nasty interaction with these mappings may occur if they are mlocked, so
> actively disallow this early.
>
> This allows a subsequent commit to remove the VM_IO check in
> __mm_populate() which otherwise requires non-MMIO mappings to be wrongly
> flagged simply as a workaround.
>
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
> ---
>  mm/gup.c | 4 ++++
>  1 file changed, 4 insertions(+)
>

Acked-by: Zi Yan <ziy@xxxxxxxxxx>



-- 
Best Regards,
Yan, Zi