[PATCH RFC v2 13/20] x86: mm: carve out the generic compile-time folded pgtable case in effective_prot()

[Yeoreum Yun]

From: "David Hildenbrand (Arm)" <david at kernel.org>

The behaviour of pXdp_get() will change with generic compile-time folded
page tables. To prepare for that, rework effective_prot() to ignore any
folded page tables entries, as it will unconditionally get called by
ptdump core with pXd_val(pXdp_get()), and we really should be ignoring
that value for folded entries.

For this, introduce ptdump_pt_level_first() to identify the first real
page-table level and update effective_prot with higher_prot only
when the current entry is not folded nor the first level.

There should be no functional change.

Signed-off-by: Yeoreum Yun <yeoreum.yun at arm.com>
---
 arch/x86/mm/dump_pagetables.c |  5 ++++-
 include/linux/ptdump.h        |  1 +
 mm/ptdump.c                   | 11 +++++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 2afa7a23340e..4e545988953a 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -27,6 +27,7 @@
  */
 struct pg_state {
 	struct ptdump_state ptdump;
+	int first_level;
 	int level;
 	pgprotval_t current_prot;
 	pgprotval_t effective_prot;
@@ -254,7 +255,7 @@ static void effective_prot(struct ptdump_state *pt_st, int level, u64 val)
 	pgprotval_t prot = val & PTE_FLAGS_MASK;
 	pgprotval_t effective;
 
-	if (level > 0) {
+	if (level > st->first_level) {
 		pgprotval_t higher_prot = st->prot_levels[level - 1];
 
 		effective = (higher_prot & prot & (_PAGE_USER | _PAGE_RW)) |
@@ -455,6 +456,8 @@ bool ptdump_walk_pgd_level_core(struct seq_file *m,
 		.seq		= m
 	};
 
+	st.first_level = ptdump_pt_level_first(mm);
+
 	ptdump_walk_pgd(&st.ptdump, mm, pgd);
 
 	if (!checkwx)
diff --git a/include/linux/ptdump.h b/include/linux/ptdump.h
index 240bd3bff18d..26fa624eac44 100644
--- a/include/linux/ptdump.h
+++ b/include/linux/ptdump.h
@@ -29,6 +29,7 @@ bool ptdump_walk_pgd_level_core(struct seq_file *m,
 				struct mm_struct *mm, pgd_t *pgd,
 				bool checkwx, bool dmesg);
 void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd);
+int ptdump_pt_level_first(struct mm_struct *mm);
 bool ptdump_check_wx(void);
 
 static inline void debug_checkwx(void)
diff --git a/mm/ptdump.c b/mm/ptdump.c
index 5851096e6f65..96676c90430f 100644
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -197,6 +197,17 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 	st->note_page_flush(st);
 }
 
+int ptdump_pt_level_first(struct mm_struct *mm)
+{
+	if (mm_pmd_folded(mm))
+		return 3;
+	if (mm_pud_folded(mm))
+		return 2;
+	if (mm_p4d_folded(mm))
+		return 1;
+	return 0;
+}
+
 static int check_wx_show(struct seq_file *m, void *v)
 {
 	if (ptdump_check_wx())

-- 
2.43.0