arm64: mte: simplify swap tag restoration logic

As a result of the patches "mm: Call arch_swap_restore() from
do_swap_page()" and "mm: Call arch_swap_restore() from unuse_pte()", there
are no circumstances in which a swapped-in page is installed in a page
table without first having arch_swap_restore() called on it.  Therefore,
we no longer need the logic in set_pte_at() that restores the tags, so
remove it.

Link: https://lkml.kernel.org/r/20230523004312.1807357-4-pcc@google.com
Link: https://linux-review.googlesource.com/id/I8ad54476f3b2d0144ccd8ce0c1d7a2963e5ff6f3
Signed-off-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: kasan-dev@googlegroups.com
Cc: kasan-dev <kasan-dev@googlegroups.com>
Cc: "Kuan-Ying Lee (李冠穎)" <Kuan-Ying.Lee@mediatek.com>
Cc: Qun-Wei Lin <qun-wei.lin@mediatek.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index c028afb..4cedbaa 100644 (file)
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -90,7 +90,7 @@ static inline bool try_page_mte_tagging(struct page *page)
 }
 
 void mte_zero_clear_page_tags(void *addr);
-void mte_sync_tags(pte_t old_pte, pte_t pte);
+void mte_sync_tags(pte_t pte);
 void mte_copy_page_tags(void *kto, const void *kfrom);
 void mte_thread_init_user(void);
 void mte_thread_switch(struct task_struct *next);
@@ -122,7 +122,7 @@ static inline bool try_page_mte_tagging(struct page *page)
 static inline void mte_zero_clear_page_tags(void *addr)
 {
 }
-static inline void mte_sync_tags(pte_t old_pte, pte_t pte)
+static inline void mte_sync_tags(pte_t pte)
 {
 }
 static inline void mte_copy_page_tags(void *kto, const void *kfrom)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 0bd18de..e8a252e 100644 (file)
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -337,18 +337,8 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
         * don't expose tags (instruction fetches don't check tags).
         */
        if (system_supports_mte() && pte_access_permitted(pte, false) &&
-           !pte_special(pte)) {
-               pte_t old_pte = READ_ONCE(*ptep);
-               /*
-                * We only need to synchronise if the new PTE has tags enabled
-                * or if swapping in (in which case another mapping may have
-                * set tags in the past even if this PTE isn't tagged).
-                * (!pte_none() && !pte_present()) is an open coded version of
-                * is_swap_pte()
-                */
-               if (pte_tagged(pte) || (!pte_none(old_pte) && !pte_present(old_pte)))
-                       mte_sync_tags(old_pte, pte);
-       }
+           !pte_special(pte) && pte_tagged(pte))
+               mte_sync_tags(pte);
 
        __check_safe_pte_update(mm, ptep, pte);
 

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 4c5ef9b..4edecaa 100644 (file)
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -35,41 +35,18 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
 EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode);
 #endif
 
-static void mte_sync_page_tags(struct page *page, pte_t old_pte,
-                              bool check_swap, bool pte_is_tagged)
-{
-       if (check_swap && is_swap_pte(old_pte)) {
-               swp_entry_t entry = pte_to_swp_entry(old_pte);
-
-               if (!non_swap_entry(entry))
-                       mte_restore_tags(entry, page);
-       }
-
-       if (!pte_is_tagged)
-               return;
-
-       if (try_page_mte_tagging(page)) {
-               mte_clear_page_tags(page_address(page));
-               set_page_mte_tagged(page);
-       }
-}
-
-void mte_sync_tags(pte_t old_pte, pte_t pte)
+void mte_sync_tags(pte_t pte)
 {
        struct page *page = pte_page(pte);
        long i, nr_pages = compound_nr(page);
-       bool check_swap = nr_pages == 1;
-       bool pte_is_tagged = pte_tagged(pte);
-
-       /* Early out if there's nothing to do */
-       if (!check_swap && !pte_is_tagged)
-               return;
 
        /* if PG_mte_tagged is set, tags have already been initialised */
-       for (i = 0; i < nr_pages; i++, page++)
-               if (!page_mte_tagged(page))
-                       mte_sync_page_tags(page, old_pte, check_swap,
-                                          pte_is_tagged);
+       for (i = 0; i < nr_pages; i++, page++) {
+               if (try_page_mte_tagging(page)) {
+                       mte_clear_page_tags(page_address(page));
+                       set_page_mte_tagged(page);
+               }
+       }
 
        /* ensure the tags are visible before the PTE is set */
        smp_wmb();