On 10.09.25 10:25, Chunyan Zhang wrote:
Hi David,
On Tue, 9 Sept 2025 at 19:42, David Hildenbrand <david@xxxxxxxxxx> wrote:
On 09.09.25 11:56, Chunyan Zhang wrote:
Some platforms can customize the PTE soft dirty bit and make it unavailable
even if the architecture allows providing the PTE resource.
Add an API which architectures can define their specific implementations
to detect if the PTE soft-dirty bit is available, on which the kernel
is running.
Signed-off-by: Chunyan Zhang <zhangchunyan@xxxxxxxxxxx>
---
fs/proc/task_mmu.c | 17 ++++++++++++++++-
include/linux/pgtable.h | 10 ++++++++++
mm/debug_vm_pgtable.c | 9 +++++----
mm/huge_memory.c | 10 ++++++----
mm/internal.h | 2 +-
mm/mremap.c | 10 ++++++----
mm/userfaultfd.c | 6 ++++--
7 files changed, 48 insertions(+), 16 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 29cca0e6d0ff..20a609ec1ba6 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 PTE soft-dirty bit is
+ * unavailable on which the kernel is running, even if the architecture
+ * allows providing the PTE resource and soft-dirty is compiled in.
+ */
+#ifdef CONFIG_MEM_SOFT_DIRTY
+ if (!pte_soft_dirty_available())
+ 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 (!pte_soft_dirty_available())
+ 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 (!pte_soft_dirty_available())
+ 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..c0e2a6dc69f4 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1538,6 +1538,15 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
#endif
#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
+
+/*
+ * Some platforms can customize the PTE soft dirty bit and make it unavailable
+ * even if the architecture allows providing the PTE resource.
+ */
+#ifndef pte_soft_dirty_available
+#define pte_soft_dirty_available() (true)
+#endif
+
#ifndef CONFIG_ARCH_ENABLE_THP_MIGRATION
static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)
{
@@ -1555,6 +1564,7 @@ static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd)
}
#endif
#else /* !CONFIG_HAVE_ARCH_SOFT_DIRTY */
+#define pte_soft_dirty_available() (false)
static inline int pte_soft_dirty(pte_t pte)
{
return 0;
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 830107b6dd08..98ed7e22ccec 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 (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) || !pte_soft_dirty_available())
I suggest that you instead make pte_soft_dirty_available() be false without CONFIG_MEM_SOFT_DIRTY.
e.g., for the default implementation
define pte_soft_dirty_available() IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)
That way you can avoid some ifefs and cleanup these checks.
Do you mean something like this:
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1538,6 +1538,16 @@ static inline pgprot_t pgprot_modify(pgprot_t
oldprot, pgprot_t newprot)
#endif
#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
+#ifndef arch_soft_dirty_available
+#define arch_soft_dirty_available() (true)
+#endif
+#define pgtable_soft_dirty_supported()
(IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) && arch_soft_dirty_available())
+
#ifndef CONFIG_ARCH_ENABLE_THP_MIGRATION
static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)
{
@@ -1555,6 +1565,7 @@ static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd)
}
#endif
#else /* !CONFIG_HAVE_ARCH_SOFT_DIRTY */
+#define pgtable_soft_dirty_supported() (false)
Maybe we can simplify to
#ifndef pgtable_soft_dirty_supported
#define pgtable_soft_dirty_supported() IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)
#endif
And then just let the arch that overrides this function just make it
respect IS_ENABLED(CONFIG_MEM_SOFT_DIRTY).
--
Cheers
David / dhildenb
