Re: [PATCH 04/22] mm: use mm_is_kernel() in generic page table code

[Kevin Brodsky <kevin.brodsky@arm.com>]

On 14/07/2026 16:03, Kevin Brodsky wrote:
> diff --git a/mm/memory.c b/mm/memory.c
> index d5e87624f692..c0244c0b0756 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3394,13 +3394,13 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
>  	spinlock_t *ptl;
>  
>  	if (create) {
> - mapped_pte = pte = (mm == &init_mm) ?
> + mapped_pte = pte = mm_is_kernel(mm) ?
>  			pte_alloc_kernel_track(pmd, addr, mask) :
>  			pte_alloc_map_lock(mm, pmd, addr, &ptl);

As noted by Sashiko, this is a little problematic because if
apply_to_page_range() is called on efi_mm, then we will end up with
__pte_alloc_kernel() taking the init_mm lock, since that's hardcoded.

That probably means we should pass the mm to __pte_alloc_kernel().

FWIW calling the kernel alloc function for efi_mm is the correct thing
to do: this ensures we use pmd_populate_kernel() and therefore kernel
page table attributes (just like efi_create_mapping()). This path is
currently never hit because EFI regions whose permissions are modified
are PTE-mapped, but it is clearly more correct to use the kernel path
for such mm's.

- Kevin