[RFC PATCH 10/34] x86: mm: carve out the generic compile-time folded pgtable case in effective_prot()

[Yeoreum Yun]

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

We want to change how pXdp_get() works 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, identify the first real page-table level and
update effective_prot only when the current entry is not folded.

There should be no functional change.

Signed-off-by: Yeoreum Yun <yeoreum.yun at arm.com>
---
 arch/x86/mm/dump_pagetables.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 2afa7a23340e9..e32848c7f26d4 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;
+	struct mm_struct *mm;
 	int level;
 	pgprotval_t current_prot;
 	pgprotval_t effective_prot;
@@ -253,8 +254,22 @@ static void effective_prot(struct ptdump_state *pt_st, int level, u64 val)
 	struct pg_state *st = container_of(pt_st, struct pg_state, ptdump);
 	pgprotval_t prot = val & PTE_FLAGS_MASK;
 	pgprotval_t effective;
+	bool first_level = false;
 
-	if (level > 0) {
+	/* Ignore folded levels ... */
+	if (((level == 0) && mm_p4d_folded(st->mm)) ||
+	    ((level == 1) && mm_pud_folded(st->mm)) ||
+	    ((level == 2) && mm_pmd_folded(st->mm)))
+		return;
+
+	/* ... and make the actual first level remember the protection. */
+	if (((level == 0)) ||
+	    ((level == 1) && mm_p4d_folded(st->mm)) ||
+	    ((level == 2) && mm_pud_folded(st->mm)) ||
+	    ((level == 3) && mm_pmd_folded(st->mm)))
+		first_level = true;
+
+	if (!first_level) {
 		pgprotval_t higher_prot = st->prot_levels[level - 1];
 
 		effective = (higher_prot & prot & (_PAGE_USER | _PAGE_RW)) |
@@ -449,6 +464,7 @@ bool ptdump_walk_pgd_level_core(struct seq_file *m,
 			.effective_prot_pgd = effective_prot_pgd,
 			.range		= ptdump_ranges
 		},
+		.mm		= mm,
 		.level = -1,
 		.to_dmesg	= dmesg,
 		.check_wx	= checkwx,
-- 
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}