Re: [PATCH v2 4/6] mm: drop HIGHPTE support altogether

["Arnd Bergmann" <arnd@arndb.de>]

On Thu, Nov 12, 2026, at 12:54, Mike Rapoport wrote:
> On Thu, Nov 12, 2026 at 12:25:26PM +0100, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>> 
>> With both x86 and arm having dropped CONFIG_HIGHPTE support, no
>> architecture is left using it, so remove the remnants in common code.
>> 
>> It is likely that further cleanups are possible in the page table
>> code but those are not obvious from the config options.
>> 
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>> ---
>>  include/linux/hugetlb.h | 5 +----
>>  include/linux/mm.h      | 1 -
>>  include/linux/pgtable.h | 9 ---------
>>  3 files changed, 1 insertion(+), 14 deletions(-)
>
> With this and arm HIGHPTE patches applied there are still a few leftovers:
>
> $ git grep  HIGHPTE
> arch/arm/configs/vt8500_v6_v7_defconfig:CONFIG_HIGHPTE=y

This got dropped in patch 5/6 in v2, but I've moved that here now.

> mm/memory.c:     * Dumping the PTE would be nice, but it's tricky with 
> CONFIG_HIGHPTE,

Added the patch below for this. Untested so far.

> mm/pgtable-generic.c: * kmapped if necessary (when CONFIG_HIGHPTE), and 
> locked against concurrent

Updated the comment and also dropped __pte_map() after I noticed that
open-coding the only caller in pte_offset_map_rw_nolock() is consistent
with that comment change:

--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -314,7 +314,7 @@ pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp)
                pmd_clear_bad(pmd);
                goto nomap;
        }
-       return __pte_map(&pmdval, addr);
+       return pte_offset_kernel(&pmdval, addr);
 nomap:
        rcu_read_unlock();
        return NULL;


> mm/userfaultfd.c:        * index ordering when CONFIG_HIGHPTE is 
> enabled. We mapped dst_pte

Dropped that comment block as it no longer applies.

> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Thanks,

      Arnd
---
Subject: [PATCH] mm: print pte in __print_bad_page_map_pgtable()

HIGHPTE support is gone now, so it's easy enough to print the
PTE here along with the upper level entries.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

diff --git a/mm/memory.c b/mm/memory.c
index ec3d9d99ccee..dabeb5568c94 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -528,9 +528,11 @@ static void __print_bad_page_map_pgtable(struct mm_struct *mm, unsigned long add
 	char p4d_str[PTVAL_STR_MAX];
 	char pud_str[PTVAL_STR_MAX];
 	char pmd_str[PTVAL_STR_MAX];
+	char pte_str[PTVAL_STR_MAX];
 	p4d_t p4d, *p4dp;
 	pud_t pud, *pudp;
 	pmd_t pmd, *pmdp;
+	pte_t pte, *ptep;
 	pgd_t *pgdp;
 
 	/*
@@ -567,13 +569,18 @@ static void __print_bad_page_map_pgtable(struct mm_struct *mm, unsigned long add
 	pmd = pmdp_get(pmdp);
 	ptval_to_str(pmd_str, pmd_val(pmd));
 
-	/*
-	 * Dumping the PTE would be nice, but it's tricky with CONFIG_HIGHPTE,
-	 * because the table should already be mapped by the caller and
-	 * doing another map would be bad. print_bad_page_map() should
-	 * already take care of printing the PTE.
-	 */
-	pr_alert("pgd:%s p4d:%s pud:%s pmd:%s\n", pgd_str, p4d_str, pud_str, pmd_str);
+	if (!pmd_present(pmd) || pmd_leaf(pmd)) {
+		pr_alert("pgd:%s p4d:%s pud:%s pmd: %s\n",
+			 pgd_str, p4d_str, pud_str, pmd_str);
+		return;
+	}
+
+	ptep = pte_offset_kernel(pmdp, addr);
+	pte = ptep_get(ptep);
+	ptval_to_str(pte_str, pte_val(pte));
+
+	pr_alert("pgd:%s p4d:%s pud:%s pmd:%s pte:%s\n",
+		 pgd_str, p4d_str, pud_str, pmd_str, pte_str);
 }
 
 /*