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+.. SPDX-License-Identifier: GPL-2.0
+
+.. _arch_page_table_helpers:
+
+===============================
+Architecture Page Table Helpers
+===============================
+
+Generic MM expects architectures (with MMU) to provide helpers to create, access
+and modify page table entries at various level for different memory functions.
+These page table helpers need to conform to a common semantics across platforms.
+Following tables describe the expected semantics which can also be tested during
+boot via CONFIG_DEBUG_VM_PGTABLE option. All future changes in here or the debug
+test need to be in sync.
+
+======================
+PTE Page Table Helpers
+======================
+
++---------------------------+--------------------------------------------------+
+| pte_same | Tests whether both PTE entries are the same |
++---------------------------+--------------------------------------------------+
+| pte_bad | Tests a non-table mapped PTE |
++---------------------------+--------------------------------------------------+
+| pte_present | Tests a valid mapped PTE |
++---------------------------+--------------------------------------------------+
+| pte_young | Tests a young PTE |
++---------------------------+--------------------------------------------------+
+| pte_dirty | Tests a dirty PTE |
++---------------------------+--------------------------------------------------+
+| pte_write | Tests a writable PTE |
++---------------------------+--------------------------------------------------+
+| pte_special | Tests a special PTE |
++---------------------------+--------------------------------------------------+
+| pte_protnone | Tests a PROT_NONE PTE |
++---------------------------+--------------------------------------------------+
+| pte_devmap | Tests a ZONE_DEVICE mapped PTE |
++---------------------------+--------------------------------------------------+
+| pte_soft_dirty | Tests a soft dirty PTE |
++---------------------------+--------------------------------------------------+
+| pte_swp_soft_dirty | Tests a soft dirty swapped PTE |
++---------------------------+--------------------------------------------------+
+| pte_mkyoung | Creates a young PTE |
++---------------------------+--------------------------------------------------+
+| pte_mkold | Creates an old PTE |
++---------------------------+--------------------------------------------------+
+| pte_mkdirty | Creates a dirty PTE |
++---------------------------+--------------------------------------------------+
+| pte_mkclean | Creates a clean PTE |
++---------------------------+--------------------------------------------------+
+| pte_mkwrite | Creates a writable PTE |
++---------------------------+--------------------------------------------------+
+| pte_mkwrprotect | Creates a write protected PTE |
++---------------------------+--------------------------------------------------+
+| pte_mkspecial | Creates a special PTE |
++---------------------------+--------------------------------------------------+
+| pte_mkdevmap | Creates a ZONE_DEVICE mapped PTE |
++---------------------------+--------------------------------------------------+
+| pte_mksoft_dirty | Creates a soft dirty PTE |
++---------------------------+--------------------------------------------------+
+| pte_clear_soft_dirty | Clears a soft dirty PTE |
++---------------------------+--------------------------------------------------+
+| pte_swp_mksoft_dirty | Creates a soft dirty swapped PTE |
++---------------------------+--------------------------------------------------+
+| pte_swp_clear_soft_dirty | Clears a soft dirty swapped PTE |
++---------------------------+--------------------------------------------------+
+| pte_mknotpresent | Invalidates a mapped PTE |
++---------------------------+--------------------------------------------------+
+| ptep_get_and_clear | Clears a PTE |
++---------------------------+--------------------------------------------------+
+| ptep_get_and_clear_full | Clears a PTE |
++---------------------------+--------------------------------------------------+
+| ptep_test_and_clear_young | Clears young from a PTE |
++---------------------------+--------------------------------------------------+
+| ptep_set_wrprotect | Converts into a write protected PTE |
++---------------------------+--------------------------------------------------+
+| ptep_set_access_flags | Converts into a more permissive PTE |
++---------------------------+--------------------------------------------------+
+
+======================
+PMD Page Table Helpers
+======================
+
++---------------------------+--------------------------------------------------+
+| pmd_same | Tests whether both PMD entries are the same |
++---------------------------+--------------------------------------------------+
+| pmd_bad | Tests a non-table mapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_leaf | Tests a leaf mapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_huge | Tests a HugeTLB mapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_trans_huge | Tests a Transparent Huge Page (THP) at PMD |
++---------------------------+--------------------------------------------------+
+| pmd_present | Tests a valid mapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_young | Tests a young PMD |
++---------------------------+--------------------------------------------------+
+| pmd_dirty | Tests a dirty PMD |
++---------------------------+--------------------------------------------------+
+| pmd_write | Tests a writable PMD |
++---------------------------+--------------------------------------------------+
+| pmd_special | Tests a special PMD |
++---------------------------+--------------------------------------------------+
+| pmd_protnone | Tests a PROT_NONE PMD |
++---------------------------+--------------------------------------------------+
+| pmd_devmap | Tests a ZONE_DEVICE mapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_soft_dirty | Tests a soft dirty PMD |
++---------------------------+--------------------------------------------------+
+| pmd_swp_soft_dirty | Tests a soft dirty swapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkyoung | Creates a young PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkold | Creates an old PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkdirty | Creates a dirty PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkclean | Creates a clean PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkwrite | Creates a writable PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkwrprotect | Creates a write protected PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkspecial | Creates a special PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkdevmap | Creates a ZONE_DEVICE mapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mksoft_dirty | Creates a soft dirty PMD |
++---------------------------+--------------------------------------------------+
+| pmd_clear_soft_dirty | Clears a soft dirty PMD |
++---------------------------+--------------------------------------------------+
+| pmd_swp_mksoft_dirty | Creates a soft dirty swapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_swp_clear_soft_dirty | Clears a soft dirty swapped PMD |
++---------------------------+--------------------------------------------------+
+| pmd_mkinvalid | Invalidates a mapped PMD [1] |
++---------------------------+--------------------------------------------------+
+| pmd_set_huge | Creates a PMD huge mapping |
++---------------------------+--------------------------------------------------+
+| pmd_clear_huge | Clears a PMD huge mapping |
++---------------------------+--------------------------------------------------+
+| pmdp_get_and_clear | Clears a PMD |
++---------------------------+--------------------------------------------------+
+| pmdp_get_and_clear_full | Clears a PMD |
++---------------------------+--------------------------------------------------+
+| pmdp_test_and_clear_young | Clears young from a PMD |
++---------------------------+--------------------------------------------------+
+| pmdp_set_wrprotect | Converts into a write protected PMD |
++---------------------------+--------------------------------------------------+
+| pmdp_set_access_flags | Converts into a more permissive PMD |
++---------------------------+--------------------------------------------------+
+
+======================
+PUD Page Table Helpers
+======================
+
++---------------------------+--------------------------------------------------+
+| pud_same | Tests whether both PUD entries are the same |
++---------------------------+--------------------------------------------------+
+| pud_bad | Tests a non-table mapped PUD |
++---------------------------+--------------------------------------------------+
+| pud_leaf | Tests a leaf mapped PUD |
++---------------------------+--------------------------------------------------+
+| pud_huge | Tests a HugeTLB mapped PUD |
++---------------------------+--------------------------------------------------+
+| pud_trans_huge | Tests a Transparent Huge Page (THP) at PUD |
++---------------------------+--------------------------------------------------+
+| pud_present | Tests a valid mapped PUD |
++---------------------------+--------------------------------------------------+
+| pud_young | Tests a young PUD |
++---------------------------+--------------------------------------------------+
+| pud_dirty | Tests a dirty PUD |
++---------------------------+--------------------------------------------------+
+| pud_write | Tests a writable PUD |
++---------------------------+--------------------------------------------------+
+| pud_devmap | Tests a ZONE_DEVICE mapped PUD |
++---------------------------+--------------------------------------------------+
+| pud_mkyoung | Creates a young PUD |
++---------------------------+--------------------------------------------------+
+| pud_mkold | Creates an old PUD |
++---------------------------+--------------------------------------------------+
+| pud_mkdirty | Creates a dirty PUD |
++---------------------------+--------------------------------------------------+
+| pud_mkclean | Creates a clean PUD |
++---------------------------+--------------------------------------------------+
+| pud_mkwrite | Creates a writable PUD |
++---------------------------+--------------------------------------------------+
+| pud_mkwrprotect | Creates a write protected PUD |
++---------------------------+--------------------------------------------------+
+| pud_mkdevmap | Creates a ZONE_DEVICE mapped PUD |
++---------------------------+--------------------------------------------------+
+| pud_mkinvalid | Invalidates a mapped PUD [1] |
++---------------------------+--------------------------------------------------+
+| pud_set_huge | Creates a PUD huge mapping |
++---------------------------+--------------------------------------------------+
+| pud_clear_huge | Clears a PUD huge mapping |
++---------------------------+--------------------------------------------------+
+| pudp_get_and_clear | Clears a PUD |
++---------------------------+--------------------------------------------------+
+| pudp_get_and_clear_full | Clears a PUD |
++---------------------------+--------------------------------------------------+
+| pudp_test_and_clear_young | Clears young from a PUD |
++---------------------------+--------------------------------------------------+
+| pudp_set_wrprotect | Converts into a write protected PUD |
++---------------------------+--------------------------------------------------+
+| pudp_set_access_flags | Converts into a more permissive PUD |
++---------------------------+--------------------------------------------------+
+
+==========================
+HugeTLB Page Table Helpers
+==========================
+
++---------------------------+--------------------------------------------------+
+| pte_huge | Tests a HugeTLB |
++---------------------------+--------------------------------------------------+
+| pte_mkhuge | Creates a HugeTLB |
++---------------------------+--------------------------------------------------+
+| huge_pte_dirty | Tests a dirty HugeTLB |
++---------------------------+--------------------------------------------------+
+| huge_pte_write | Tests a writable HugeTLB |
++---------------------------+--------------------------------------------------+
+| huge_pte_mkdirty | Creates a dirty HugeTLB |
++---------------------------+--------------------------------------------------+
+| huge_pte_mkwrite | Creates a writable HugeTLB |
++---------------------------+--------------------------------------------------+
+| huge_pte_mkwrprotect | Creates a write protected HugeTLB |
++---------------------------+--------------------------------------------------+
+| huge_ptep_get_and_clear | Clears a HugeTLB |
++---------------------------+--------------------------------------------------+
+| huge_ptep_set_wrprotect | Converts into a write protected HugeTLB |
++---------------------------+--------------------------------------------------+
+| huge_ptep_set_access_flags | Converts into a more permissive HugeTLB |
++---------------------------+--------------------------------------------------+
+
+========================
+SWAP Page Table Helpers
+========================
+
++---------------------------+--------------------------------------------------+
+| __pte_to_swp_entry | Creates a swapped entry (arch) from a mapped PTE |
++---------------------------+--------------------------------------------------+
+| __swp_to_pte_entry | Creates a mapped PTE from a swapped entry (arch) |
++---------------------------+--------------------------------------------------+
+| __pmd_to_swp_entry | Creates a swapped entry (arch) from a mapped PMD |
++---------------------------+--------------------------------------------------+
+| __swp_to_pmd_entry | Creates a mapped PMD from a swapped entry (arch) |
++---------------------------+--------------------------------------------------+
+| is_migration_entry | Tests a migration (read or write) swapped entry |
++---------------------------+--------------------------------------------------+
+| is_write_migration_entry | Tests a write migration swapped entry |
++---------------------------+--------------------------------------------------+
+| make_migration_entry_read | Converts into read migration swapped entry |
++---------------------------+--------------------------------------------------+
+| make_migration_entry | Creates a migration swapped entry (read or write)|
++---------------------------+--------------------------------------------------+
+
+[1] https://lore.kernel.org/linux-mm/20181017020930.GN30832@redhat.com/