Re: [PATCH RFC v4 04/12] mm/gup: let check_vma_flags() ignore selected VMA flags

[Rik van Riel]

On Mon, 2026-07-27 at 19:40 -0700, John Hubbard wrote:
> 
> Perhaps it is best to replace the mask with a single-purpose internal
> GUP flag, such as FOLL_PFNMAP_COW, and apply it only to the
> special-mapping gate:
> 
> 	if (vm_flags & (VM_IO | VM_PFNMAP) &&
> 	    (!(gup_flags & FOLL_PFNMAP_COW) ||
> 	     !(vm_flags & VM_PFNMAP)))
> 		return -EFAULT;
> 
> This permits the later caller to examine a VM_PFNMAP mapping while
> keeping VM_IO-only mappings and every other VMA check unchanged.

Nice idea. I will implement that for v5!


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