[PATCH 17/22] mm: pagewalk: drop redundant address check for kernel mm walks

[Kevin Brodsky]

Commit 8b1cb4a2e819 ("mm/pagewalk: fix EFI_PGT_DUMP of
espfix area") made no-VMA page table walks use
pte_offset_kernel() for any address above TASK_SIZE. This avoided
pte_offset_map() validation on EFI page table dumps, where efi_mm
could walk x86 espfix PMDs that intentionally look bad to pmd_bad().

efi_mm is now marked with MMF_KERNEL, and no-VMA walks use
mm_is_kernel() to select pte_offset_kernel() for kernel mm's. As a
result we no longer need to handle the EFI_PGT_DUMP case explicitly.The
address check is therefore redundant for EFI_PGT_DUMP and makes the
condition harder to reason about.

Remove the address check and associated comment; mm_is_kernel()
should be sufficient on its own.

Tested by booting x86 QEMU with CONFIG_EFI_PGT_DUMP=y and reading
/sys/kernel/debug/page_tables/efi.

Assisted-by: Codex:GPT-5.5
Signed-off-by: Kevin Brodsky <kevin.brodsky at arm.com>
---
 mm/pagewalk.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index a3f47d1de3c5..0dd9d4ad9b68 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -68,17 +68,14 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 	if (walk->no_vma) {
 		/*
 		 * pte_offset_map() might apply user-specific validation.
-		 * Indeed, on x86_64 the pmd entries set up by init_espfix_ap()
-		 * fit its pmd_bad() check (_PAGE_NX set and _PAGE_RW clear),
-		 * and CONFIG_EFI_PGT_DUMP efi_mm goes so far as to walk them.
 		 */
-		if (mm_is_kernel(walk->mm) || addr >= TASK_SIZE)
+		if (mm_is_kernel(walk->mm))
 			pte = pte_offset_kernel(pmd, addr);
 		else
 			pte = pte_offset_map(pmd, addr);
 		if (pte) {
 			err = walk_pte_range_inner(pte, addr, end, walk);
-			if (!mm_is_kernel(walk->mm) && addr < TASK_SIZE)
+			if (!mm_is_kernel(walk->mm))
 				pte_unmap(pte);
 		}
 	} else {

-- 
2.51.2