On 11.09.25 11:55, Chunyan Zhang wrote:
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.
Thinking to myself: maybe pgtable_supports_soft_dirty() would read better
Whatever you prefer.
Signed-off-by: Chunyan Zhang <zhangchunyan@xxxxxxxxxxx>
---
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
You can now drop the ifdef.
But, I wonder if could we instead just stop setting the flag. Then we don't
have to worry about any VM_SOFTDIRTY checks.
Something like the following
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 892fe5dbf9de0..8b8bf63a32ef7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -783,6 +783,7 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
static inline void vm_flags_init(struct vm_area_struct *vma,
vm_flags_t flags)
{
+ VM_WARN_ON_ONCE(!pgtable_soft_dirty_supported() && (flags & VM_SOFTDIRTY));
ACCESS_PRIVATE(vma, __vm_flags) = flags;
}
@@ -801,6 +802,7 @@ static inline void vm_flags_reset(struct vm_area_struct *vma,
static inline void vm_flags_reset_once(struct vm_area_struct *vma,
vm_flags_t flags)
{
+ VM_WARN_ON_ONCE(!pgtable_soft_dirty_supported() && (flags & VM_SOFTDIRTY));
vma_assert_write_locked(vma);
WRITE_ONCE(ACCESS_PRIVATE(vma, __vm_flags), flags);
}
@@ -808,6 +810,7 @@ static inline void vm_flags_reset_once(struct vm_area_struct *vma,
static inline void vm_flags_set(struct vm_area_struct *vma,
vm_flags_t flags)
{
+ VM_WARN_ON_ONCE(!pgtable_soft_dirty_supported() && (flags & VM_SOFTDIRTY));
vma_start_write(vma);
ACCESS_PRIVATE(vma, __vm_flags) |= flags;
}
diff --git a/mm/mmap.c b/mm/mmap.c
index 5fd3b80fda1d5..40cb3fbf9a247 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1451,8 +1451,10 @@ static struct vm_area_struct *__install_special_mapping(
return ERR_PTR(-ENOMEM);
vma_set_range(vma, addr, addr + len, 0);
- vm_flags_init(vma, (vm_flags | mm->def_flags |
- VM_DONTEXPAND | VM_SOFTDIRTY) & ~VM_LOCKED_MASK);
+ vm_flags |= mm->def_flags | VM_DONTEXPAND;
+ if (pgtable_soft_dirty_supported())
+ vm_flags |= VM_SOFTDIRTY;
+ vm_flags_init(vma, vm_flags & ~VM_LOCKED_MASK);
vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
vma->vm_ops = ops;
diff --git a/mm/vma.c b/mm/vma.c
index abe0da33c8446..16a1ed2a6199c 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -2551,7 +2551,8 @@ static void __mmap_complete(struct mmap_state *map, struct vm_area_struct *vma)
* then new mapped in-place (which must be aimed as
* a completely new data area).
*/
- vm_flags_set(vma, VM_SOFTDIRTY);
+ if (pgtable_soft_dirty_supported())
+ vm_flags_set(vma, VM_SOFTDIRTY);
vma_set_page_prot(vma);
}
@@ -2819,7 +2820,8 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
mm->data_vm += len >> PAGE_SHIFT;
if (vm_flags & VM_LOCKED)
mm->locked_vm += (len >> PAGE_SHIFT);
- vm_flags_set(vma, VM_SOFTDIRTY);
+ if (pgtable_soft_dirty_supported())
+ vm_flags_set(vma, VM_SOFTDIRTY);
return 0;
mas_store_fail:
diff --git a/mm/vma_exec.c b/mm/vma_exec.c
index 922ee51747a68..c06732a5a620a 100644
--- a/mm/vma_exec.c
+++ b/mm/vma_exec.c
@@ -107,6 +107,7 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
int create_init_stack_vma(struct mm_struct *mm, struct vm_area_struct **vmap,
unsigned long *top_mem_p)
{
+ unsigned long flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
int err;
struct vm_area_struct *vma = vm_area_alloc(mm);
@@ -137,7 +138,9 @@ int create_init_stack_vma(struct mm_struct *mm, struct vm_area_struct **vmap,
BUILD_BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
vma->vm_end = STACK_TOP_MAX;
vma->vm_start = vma->vm_end - PAGE_SIZE;
- vm_flags_init(vma, VM_SOFTDIRTY | VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP);
+ if (pgtable_soft_dirty_supported())
+ flags |= VM_SOFTDIRTY;
+ vm_flags_init(vma, flags);
vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
err = insert_vm_struct(mm, vma);
+
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);
That would all be handled with the above never-set-VM_SOFTDIRTY.
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);
+ }
+
Wondering, should simply the arch take care of that and we can just clal
pmd_swp_mksoft_dirty / pmd_mksoft_dirty?
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;
That should be handled with the above never-set-VM_SOFTDIRTY.
/*
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;
}
--
Cheers
David / dhildenb
