mm/mapping_dirty_helpers: update huge page-table entry callbacks

Following the update of pagewalk code commit a07984d48146 ("mm: pagewalk:
add p4d_entry() and pgd_entry()") we can modify the mapping_dirty_helpers'
huge page-table entry callbacks to avoid splitting when a huge pud or -pmd
is encountered.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Steven Price <steven.price@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200203154305.15045-1-thomas_os@shipmail.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c
index 71070dd..2c7d036 100644 (file)
--- a/mm/mapping_dirty_helpers.c
+++ b/mm/mapping_dirty_helpers.c
@@ -111,26 +111,60 @@ static int clean_record_pte(pte_t *pte, unsigned long addr,
        return 0;
 }
 
-/* wp_clean_pmd_entry - The pagewalk pmd callback. */
+/*
+ * wp_clean_pmd_entry - The pagewalk pmd callback.
+ *
+ * Dirty-tracking should take place on the PTE level, so
+ * WARN() if encountering a dirty huge pmd.
+ * Furthermore, never split huge pmds, since that currently
+ * causes dirty info loss. The pagefault handler should do
+ * that if needed.
+ */
 static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
                              struct mm_walk *walk)
 {
-       /* Dirty-tracking should be handled on the pte level */
        pmd_t pmdval = pmd_read_atomic(pmd);
 
+       if (!pmd_trans_unstable(&pmdval))
+               return 0;
+
+       if (pmd_none(pmdval)) {
+               walk->action = ACTION_AGAIN;
+               return 0;
+       }
+
+       /* Huge pmd, present or migrated */
+       walk->action = ACTION_CONTINUE;
        if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
                WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
 
        return 0;
 }
 
-/* wp_clean_pud_entry - The pagewalk pud callback. */
+/*
+ * wp_clean_pud_entry - The pagewalk pud callback.
+ *
+ * Dirty-tracking should take place on the PTE level, so
+ * WARN() if encountering a dirty huge puds.
+ * Furthermore, never split huge puds, since that currently
+ * causes dirty info loss. The pagefault handler should do
+ * that if needed.
+ */
 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
                              struct mm_walk *walk)
 {
-       /* Dirty-tracking should be handled on the pte level */
        pud_t pudval = READ_ONCE(*pud);
 
+       if (!pud_trans_unstable(&pudval))
+               return 0;
+
+       if (pud_none(pudval)) {
+               walk->action = ACTION_AGAIN;
+               return 0;
+       }
+
+       /* Huge pud */
+       walk->action = ACTION_CONTINUE;
        if (pud_trans_huge(pudval) || pud_devmap(pudval))
                WARN_ON(pud_write(pudval) || pud_dirty(pudval));