mm: always compile in pte markers

Patch series "mm: Use pte marker for swapin errors".

This series uses the pte marker to replace the swapin error swap entry,
then we save one more swap entry slot for swap devices.  A new pte marker
bit is defined.

This patch (of 2):

The PTE markers code is tiny and now it's enabled for most of the
distributions.  It's fine to keep it as-is, but to make a broader use of
it (e.g.  replacing read error swap entry) it needs to be there always
otherwise we need special code path to take care of !PTE_MARKER case.

It'll be easier just make pte marker always exist.  Use this chance to
extend its usage to anonymous too by simply touching up some of the old
comments, because it'll be used for anonymous pages in the follow up
patches.

Link: https://lkml.kernel.org/r/20221030214151.402274-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20221030214151.402274-2-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Huang Ying <ying.huang@intel.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 369d7799205dd9400e554ae3a756f8b7dad8efb5..211aeca9bfa7f1cdb1a4e53cbfba90b832e9a9f1 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -60,17 +60,13 @@ static inline int current_is_kswapd(void)
                             SWP_MIGRATION_NUM + SWP_DEVICE_NUM + \
                             SWP_PTE_MARKER_NUM)
 /*
- * PTE markers are used to persist information onto PTEs that are mapped with
- * file-backed memories.  As its name "PTE" hints, it should only be applied to
- * the leaves of pgtables.
+ * PTE markers are used to persist information onto PTEs that otherwise
+ * should be a none pte.  As its name "PTE" hints, it should only be
+ * applied to the leaves of pgtables.
  */
-#ifdef CONFIG_PTE_MARKER
 #define SWP_PTE_MARKER_NUM 1
 #define SWP_PTE_MARKER     (MAX_SWAPFILES + SWP_HWPOISON_NUM + \
                            SWP_MIGRATION_NUM + SWP_DEVICE_NUM)
-#else
-#define SWP_PTE_MARKER_NUM 0
-#endif
 
 /*
  * Unaddressable device memory support. See include/linux/hmm.h and

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 3ba9bf56899daac042e616da294e40c7a0c31c63..35c1fe62d2e1aedb21604c0c9778c151fa68a659 100644 (file)
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -412,8 +412,6 @@ typedef unsigned long pte_marker;
 #define  PTE_MARKER_UFFD_WP  BIT(0)
 #define  PTE_MARKER_MASK     (PTE_MARKER_UFFD_WP)
 
-#ifdef CONFIG_PTE_MARKER
-
 static inline swp_entry_t make_pte_marker_entry(pte_marker marker)
 {
        return swp_entry(SWP_PTE_MARKER, marker);
@@ -434,32 +432,6 @@ static inline bool is_pte_marker(pte_t pte)
        return is_swap_pte(pte) && is_pte_marker_entry(pte_to_swp_entry(pte));
 }
 
-#else /* CONFIG_PTE_MARKER */
-
-static inline swp_entry_t make_pte_marker_entry(pte_marker marker)
-{
-       /* This should never be called if !CONFIG_PTE_MARKER */
-       WARN_ON_ONCE(1);
-       return swp_entry(0, 0);
-}
-
-static inline bool is_pte_marker_entry(swp_entry_t entry)
-{
-       return false;
-}
-
-static inline pte_marker pte_marker_get(swp_entry_t entry)
-{
-       return 0;
-}
-
-static inline bool is_pte_marker(pte_t pte)
-{
-       return false;
-}
-
-#endif /* CONFIG_PTE_MARKER */
-
 static inline pte_t make_pte_marker(pte_marker marker)
 {
        return swp_entry_to_pte(make_pte_marker_entry(marker));
@@ -477,9 +449,6 @@ static inline pte_t make_pte_marker(pte_marker marker)
  * memory, kernel-only memory (including when the system is during-boot),
  * non-ram based generic file-system.  It's fine to be used even there, but the
  * extra pte marker check will be pure overhead.
- *
- * For systems configured with !CONFIG_PTE_MARKER this will be automatically
- * optimized to pte_none().
  */
 static inline int pte_none_mostly(pte_t pte)
 {

diff --git a/mm/Kconfig b/mm/Kconfig
index 57e1d8c5b505287c3c0c81474d0daaa8f333e3d1..4b28800d9be1651c3938700cfaa0b99d0f0ba23a 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1107,17 +1107,10 @@ config HAVE_ARCH_USERFAULTFD_MINOR
        help
          Arch has userfaultfd minor fault support
 
-config PTE_MARKER
-       bool
-
-       help
-         Allows to create marker PTEs for file-backed memory.
-
 config PTE_MARKER_UFFD_WP
        bool "Userfaultfd write protection support for shmem/hugetlbfs"
        default y
        depends on HAVE_ARCH_USERFAULTFD_WP
-       select PTE_MARKER
 
        help
          Allows to create marker PTEs for userfaultfd write protection

diff --git a/mm/memory.c b/mm/memory.c
index 659620b6770fdd20bcc89036c698e1eea6806a62..b79d275337223a7ae4e9056093362a8b6ac790ea 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3662,11 +3662,10 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
        unsigned long marker = pte_marker_get(entry);
 
        /*
-        * PTE markers should always be with file-backed memories, and the
-        * marker should never be empty.  If anything weird happened, the best
-        * thing to do is to kill the process along with its mm.
+        * PTE markers should never be empty.  If anything weird happened,
+        * the best thing to do is to kill the process along with its mm.
         */
-       if (WARN_ON_ONCE(vma_is_anonymous(vmf->vma) || !marker))
+       if (WARN_ON_ONCE(!marker))
                return VM_FAULT_SIGBUS;
 
        if (pte_marker_entry_uffd_wp(entry))