[PATCH v11 1/5] mm: softdirty: Add pgtable_soft_dirty_supported()
Chunyan Zhang
zhangchunyan at iscas.ac.cn
Thu Sep 11 02:55:58 PDT 2025
Some platforms can customize the PTE PMD entry soft-dirty bit making it
unavailable even if the architecture provides the resource.
Add an API which architectures can define their specific implementations
to detect if soft-dirty bit is available on which device the kernel is
running.
Signed-off-by: Chunyan Zhang <zhangchunyan at iscas.ac.cn>
---
fs/proc/task_mmu.c | 17 ++++++++++++++++-
include/linux/pgtable.h | 12 ++++++++++++
mm/debug_vm_pgtable.c | 10 +++++-----
mm/huge_memory.c | 13 +++++++------
mm/internal.h | 2 +-
mm/mremap.c | 13 +++++++------
mm/userfaultfd.c | 10 ++++------
7 files changed, 52 insertions(+), 25 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 29cca0e6d0ff..9e8083b6d4cd 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1058,7 +1058,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
* -Werror=unterminated-string-initialization warning
* with GCC 15
*/
- static const char mnemonics[BITS_PER_LONG][3] = {
+ static char mnemonics[BITS_PER_LONG][3] = {
/*
* In case if we meet a flag we don't know about.
*/
@@ -1129,6 +1129,16 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
[ilog2(VM_SEALED)] = "sl",
#endif
};
+/*
+ * We should remove the VM_SOFTDIRTY flag if the soft-dirty bit is
+ * unavailable on which the kernel is running, even if the architecture
+ * provides the resource and soft-dirty is compiled in.
+ */
+#ifdef CONFIG_MEM_SOFT_DIRTY
+ if (!pgtable_soft_dirty_supported())
+ mnemonics[ilog2(VM_SOFTDIRTY)][0] = 0;
+#endif
+
size_t i;
seq_puts(m, "VmFlags: ");
@@ -1531,6 +1541,8 @@ static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr,
static inline void clear_soft_dirty(struct vm_area_struct *vma,
unsigned long addr, pte_t *pte)
{
+ if (!pgtable_soft_dirty_supported())
+ return;
/*
* The soft-dirty tracker uses #PF-s to catch writes
* to pages, so write-protect the pte as well. See the
@@ -1566,6 +1578,9 @@ static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,
{
pmd_t old, pmd = *pmdp;
+ if (!pgtable_soft_dirty_supported())
+ return;
+
if (pmd_present(pmd)) {
/* See comment in change_huge_pmd() */
old = pmdp_invalidate(vma, addr, pmdp);
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 4c035637eeb7..2a3578a4ae4c 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1537,6 +1537,18 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
#define arch_start_context_switch(prev) do {} while (0)
#endif
+/*
+ * Some platforms can customize the PTE soft-dirty bit making it unavailable
+ * even if the architecture provides the resource.
+ * Adding this API allows architectures to add their own checks for the
+ * devices on which the kernel is running.
+ * Note: When overiding it, please make sure the CONFIG_MEM_SOFT_DIRTY
+ * is part of this macro.
+ */
+#ifndef pgtable_soft_dirty_supported
+#define pgtable_soft_dirty_supported() IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)
+#endif
+
#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
#ifndef CONFIG_ARCH_ENABLE_THP_MIGRATION
static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 830107b6dd08..b32ce2b0b998 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -690,7 +690,7 @@ static void __init pte_soft_dirty_tests(struct pgtable_debug_args *args)
{
pte_t pte = pfn_pte(args->fixed_pte_pfn, args->page_prot);
- if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+ if (!pgtable_soft_dirty_supported())
return;
pr_debug("Validating PTE soft dirty\n");
@@ -702,7 +702,7 @@ static void __init pte_swap_soft_dirty_tests(struct pgtable_debug_args *args)
{
pte_t pte;
- if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+ if (!pgtable_soft_dirty_supported())
return;
pr_debug("Validating PTE swap soft dirty\n");
@@ -718,7 +718,7 @@ static void __init pmd_soft_dirty_tests(struct pgtable_debug_args *args)
{
pmd_t pmd;
- if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+ if (!pgtable_soft_dirty_supported())
return;
if (!has_transparent_hugepage())
@@ -734,8 +734,8 @@ static void __init pmd_swap_soft_dirty_tests(struct pgtable_debug_args *args)
{
pmd_t pmd;
- if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) ||
- !IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION))
+ if (!pgtable_soft_dirty_supported() ||
+ !IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION))
return;
if (!has_transparent_hugepage())
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9c38a95e9f09..218d430a2ec6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2271,12 +2271,13 @@ static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
static pmd_t move_soft_dirty_pmd(pmd_t pmd)
{
-#ifdef CONFIG_MEM_SOFT_DIRTY
- if (unlikely(is_pmd_migration_entry(pmd)))
- pmd = pmd_swp_mksoft_dirty(pmd);
- else if (pmd_present(pmd))
- pmd = pmd_mksoft_dirty(pmd);
-#endif
+ if (pgtable_soft_dirty_supported()) {
+ if (unlikely(is_pmd_migration_entry(pmd)))
+ pmd = pmd_swp_mksoft_dirty(pmd);
+ else if (pmd_present(pmd))
+ pmd = pmd_mksoft_dirty(pmd);
+ }
+
return pmd;
}
diff --git a/mm/internal.h b/mm/internal.h
index 45b725c3dc03..c6ca62f8ecf3 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1538,7 +1538,7 @@ static inline bool vma_soft_dirty_enabled(struct vm_area_struct *vma)
* VM_SOFTDIRTY is defined as 0x0, then !(vm_flags & VM_SOFTDIRTY)
* will be constantly true.
*/
- if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+ if (!pgtable_soft_dirty_supported())
return false;
/*
diff --git a/mm/mremap.c b/mm/mremap.c
index e618a706aff5..7beb3114dbf5 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -162,12 +162,13 @@ static pte_t move_soft_dirty_pte(pte_t pte)
* Set soft dirty bit so we can notice
* in userspace the ptes were moved.
*/
-#ifdef CONFIG_MEM_SOFT_DIRTY
- if (pte_present(pte))
- pte = pte_mksoft_dirty(pte);
- else if (is_swap_pte(pte))
- pte = pte_swp_mksoft_dirty(pte);
-#endif
+ if (pgtable_soft_dirty_supported()) {
+ if (pte_present(pte))
+ pte = pte_mksoft_dirty(pte);
+ else if (is_swap_pte(pte))
+ pte = pte_swp_mksoft_dirty(pte);
+ }
+
return pte;
}
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 45e6290e2e8b..85f43479b67a 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1065,9 +1065,8 @@ static int move_present_pte(struct mm_struct *mm,
orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot);
/* Set soft dirty bit so userspace can notice the pte was moved */
-#ifdef CONFIG_MEM_SOFT_DIRTY
- orig_dst_pte = pte_mksoft_dirty(orig_dst_pte);
-#endif
+ if (pgtable_soft_dirty_supported())
+ orig_dst_pte = pte_mksoft_dirty(orig_dst_pte);
if (pte_dirty(orig_src_pte))
orig_dst_pte = pte_mkdirty(orig_dst_pte);
orig_dst_pte = pte_mkwrite(orig_dst_pte, dst_vma);
@@ -1134,9 +1133,8 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma,
}
orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
-#ifdef CONFIG_MEM_SOFT_DIRTY
- orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte);
-#endif
+ if (pgtable_soft_dirty_supported())
+ orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte);
set_pte_at(mm, dst_addr, dst_pte, orig_src_pte);
double_pt_unlock(dst_ptl, src_ptl);
--
2.34.1
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