[PATCH v6 18/19] x86: mm: Convert ptdump_walk_pgd_level_core() to take an mm_struct

[Steven Price]

An mm_struct is needed to enable x86 to use of the generic
walk_page_range() function.

In the case of walking the user page tables (when
CONFIG_PAGE_TABLE_ISOLATION is enabled), it is necessary to create a
fake_mm structure because there isn't an mm_struct with a pointer
to the pgd of the user page tables. This fake_mm structure is
initialised with the minimum necessary for the generic page walk code.

Signed-off-by: Steven Price <steven.pr...@arm.com>
---
 arch/x86/mm/dump_pagetables.c | 36 ++++++++++++++++++++---------------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 40b3f1da6e15..c0fbb9e5a790 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -111,8 +111,6 @@ static struct addr_marker address_markers[] = {
        [END_OF_SPACE_NR]       = { -1,                 NULL }
 };
 
-#define INIT_PGD       ((pgd_t *) &init_top_pgt)
-
 #else /* CONFIG_X86_64 */
 
 enum address_markers_idx {
@@ -147,8 +145,6 @@ static struct addr_marker address_markers[] = {
        [END_OF_SPACE_NR]       = { -1,                 NULL }
 };
 
-#define INIT_PGD       (swapper_pg_dir)
-
 #endif /* !CONFIG_X86_64 */
 
 /* Multipliers for offsets within the PTEs */
@@ -522,10 +518,10 @@ static inline bool is_hypervisor_range(int idx)
 #endif
 }
 
-static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
+static void ptdump_walk_pgd_level_core(struct seq_file *m, struct mm_struct 
*mm,
                                       bool checkwx, bool dmesg)
 {
-       pgd_t *start = pgd;
+       pgd_t *start = mm->pgd;
        pgprotval_t prot, eff;
        int i;
        struct pg_state st = {};
@@ -572,39 +568,49 @@ static void ptdump_walk_pgd_level_core(struct seq_file 
*m, pgd_t *pgd,
 
 void ptdump_walk_pgd_level(struct seq_file *m, struct mm_struct *mm)
 {
-       ptdump_walk_pgd_level_core(m, mm->pgd, false, true);
+       ptdump_walk_pgd_level_core(m, mm, false, true);
 }
 
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+static void ptdump_walk_pgd_level_user_core(struct seq_file *m,
+                                           struct mm_struct *mm,
+                                           bool checkwx, bool dmesg)
+{
+       struct mm_struct fake_mm = {
+               .pgd = kernel_to_user_pgdp(mm->pgd)
+       };
+       init_rwsem(&fake_mm.mmap_sem);
+       ptdump_walk_pgd_level_core(m, &fake_mm, checkwx, dmesg);
+}
+#endif
+
 void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm,
                                   bool user)
 {
-       pgd_t *pgd = mm->pgd;
 #ifdef CONFIG_PAGE_TABLE_ISOLATION
        if (user && static_cpu_has(X86_FEATURE_PTI))
-               pgd = kernel_to_user_pgdp(pgd);
+               ptdump_walk_pgd_level_user_core(m, mm, false, false);
+       else
 #endif
-       ptdump_walk_pgd_level_core(m, pgd, false, false);
+               ptdump_walk_pgd_level_core(m, mm, false, false);
 }
 EXPORT_SYMBOL_GPL(ptdump_walk_pgd_level_debugfs);
 
 void ptdump_walk_user_pgd_level_checkwx(void)
 {
 #ifdef CONFIG_PAGE_TABLE_ISOLATION
-       pgd_t *pgd = INIT_PGD;
-
        if (!(__supported_pte_mask & _PAGE_NX) ||
            !static_cpu_has(X86_FEATURE_PTI))
                return;
 
        pr_info("x86/mm: Checking user space page tables\n");
-       pgd = kernel_to_user_pgdp(pgd);
-       ptdump_walk_pgd_level_core(NULL, pgd, true, false);
+       ptdump_walk_pgd_level_user_core(NULL, &init_mm, true, false);
 #endif
 }
 
 void ptdump_walk_pgd_level_checkwx(void)
 {
-       ptdump_walk_pgd_level_core(NULL, INIT_PGD, true, false);
+       ptdump_walk_pgd_level_core(NULL, &init_mm, true, false);
 }
 
 static int __init pt_dump_init(void)
-- 
2.20.1