[PATCH] mm: introduce pmd|pte_need_soft_dirty_wp helpers for softdirty write-protect

[PATCH] mm: introduce pmd|pte_need_soft_dirty_wp helpers for softdirty write-protect

[Barry Song]

From: Barry Song <v-songbaohua@oppo.com>

This patch introduces the pte_need_soft_dirty_wp and
pmd_need_soft_dirty_wp helpers to determine if write protection is
required for softdirty tracking. This can enhance code readability
and improve its overall appearance.

These new helpers are utilized in gup, huge_memory, and protect,
and are particularly applied in do_swap_page() to optimize a
softdirty scenario where mkwrite can still be performed.

Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 -v1:
 this is suggested by David here:
 https://lore.kernel.org/linux-mm/baf84b51-7e8a-4da8-9662-3f5cf14ad6f6@redhat.com/
 thanks!

 mm/gup.c         |  4 ++--
 mm/huge_memory.c |  2 +-
 mm/internal.h    | 10 ++++++++++
 mm/memory.c      |  2 +-
 mm/mprotect.c    |  2 +-
 5 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 83e279731d1b..756d5416df9c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -820,7 +820,7 @@ static inline bool can_follow_write_pmd(pmd_t pmd, struct page *page,
 		return false;
 
 	/* ... and a write-fault isn't required for other reasons. */
-	if (vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd))
+	if (pmd_need_soft_dirty_wp(vma, pmd))
 		return false;
 	return !userfaultfd_huge_pmd_wp(vma, pmd);
 }
@@ -941,7 +941,7 @@ static inline bool can_follow_write_pte(pte_t pte, struct page *page,
 		return false;
 
 	/* ... and a write-fault isn't required for other reasons. */
-	if (vma_soft_dirty_enabled(vma) && !pte_soft_dirty(pte))
+	if (pte_need_soft_dirty_wp(vma, pte))
 		return false;
 	return !userfaultfd_pte_wp(vma, pte);
 }
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 3fbcd77f5957..8fbb62f6e491 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1625,7 +1625,7 @@ static inline bool can_change_pmd_writable(struct vm_area_struct *vma,
 		return false;
 
 	/* Do we need write faults for softdirty tracking? */
-	if (vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd))
+	if (pmd_need_soft_dirty_wp(vma, pmd))
 		return false;
 
 	/* Do we need write faults for uffd-wp tracking? */
diff --git a/mm/internal.h b/mm/internal.h
index 12e95fdf61e9..51551626da68 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1348,6 +1348,16 @@ static inline bool vma_soft_dirty_enabled(struct vm_area_struct *vma)
 	return !(vma->vm_flags & VM_SOFTDIRTY);
 }
 
+static inline bool pmd_need_soft_dirty_wp(struct vm_area_struct *vma, pmd_t pmd)
+{
+	return vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd);
+}
+
+static inline bool pte_need_soft_dirty_wp(struct vm_area_struct *vma, pte_t pte)
+{
+	return vma_soft_dirty_enabled(vma) && !pte_soft_dirty(pte);
+}
+
 static inline void vma_iter_config(struct vma_iterator *vmi,
 		unsigned long index, unsigned long last)
 {
diff --git a/mm/memory.c b/mm/memory.c
index db9130488231..6307c43796aa 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4322,7 +4322,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	if (!folio_test_ksm(folio) &&
 	    (exclusive || folio_ref_count(folio) == 1)) {
 		if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
-		    !vma_soft_dirty_enabled(vma)) {
+		    !pte_need_soft_dirty_wp(vma, pte)) {
 			pte = pte_mkwrite(pte, vma);
 			if (vmf->flags & FAULT_FLAG_WRITE) {
 				pte = pte_mkdirty(pte);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 888ef66468db..5aea9ad11ae1 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -53,7 +53,7 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr,
 		return false;
 
 	/* Do we need write faults for softdirty tracking? */
-	if (vma_soft_dirty_enabled(vma) && !pte_soft_dirty(pte))
+	if (pte_need_soft_dirty_wp(vma, pte))
 		return false;
 
 	/* Do we need write faults for uffd-wp tracking? */
-- 
2.34.1

Re: [PATCH] mm: introduce pmd|pte_need_soft_dirty_wp helpers for softdirty write-protect

[David Hildenbrand]

On 06.06.24 05:40, Barry Song wrote:
> From: Barry Song <v-songbaohua@oppo.com>
> 
> This patch introduces the pte_need_soft_dirty_wp and
> pmd_need_soft_dirty_wp helpers to determine if write protection is
> required for softdirty tracking. This can enhance code readability
> and improve its overall appearance.
> 
> These new helpers are utilized in gup, huge_memory, and protect,
> and are particularly applied in do_swap_page() to optimize a
> softdirty scenario where mkwrite can still be performed.

[...]

> +static inline bool pmd_need_soft_dirty_wp(struct vm_area_struct *vma, pmd_t pmd)
> +{
> +	return vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd);
> +}
> +
> +static inline bool pte_need_soft_dirty_wp(struct vm_area_struct *vma, pte_t pte)
> +{
> +	return vma_soft_dirty_enabled(vma) && !pte_soft_dirty(pte);
> +}
> +

Should these be "needs" ? I tend to like these names/semantics.


>   static inline void vma_iter_config(struct vma_iterator *vmi,
>   		unsigned long index, unsigned long last)
>   {
> diff --git a/mm/memory.c b/mm/memory.c
> index db9130488231..6307c43796aa 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4322,7 +4322,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>   	if (!folio_test_ksm(folio) &&
>   	    (exclusive || folio_ref_count(folio) == 1)) {
>   		if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
> -		    !vma_soft_dirty_enabled(vma)) {
> +		    !pte_need_soft_dirty_wp(vma, pte)) {
>   			pte = pte_mkwrite(pte, vma);

I would move that into a separate patch, as it's not a simple conversion.

-- 
Cheers,

David / dhildenb

Re: [PATCH] mm: introduce pmd|pte_need_soft_dirty_wp helpers for softdirty write-protect

[Barry Song]

On Fri, Jun 7, 2024 at 8:46 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 06.06.24 05:40, Barry Song wrote:
> > From: Barry Song <v-songbaohua@oppo.com>
> >
> > This patch introduces the pte_need_soft_dirty_wp and
> > pmd_need_soft_dirty_wp helpers to determine if write protection is
> > required for softdirty tracking. This can enhance code readability
> > and improve its overall appearance.
> >
> > These new helpers are utilized in gup, huge_memory, and protect,
> > and are particularly applied in do_swap_page() to optimize a
> > softdirty scenario where mkwrite can still be performed.
>
> [...]
>
> > +static inline bool pmd_need_soft_dirty_wp(struct vm_area_struct *vma, pmd_t pmd)
> > +{
> > +     return vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd);
> > +}
> > +
> > +static inline bool pte_need_soft_dirty_wp(struct vm_area_struct *vma, pte_t pte)
> > +{
> > +     return vma_soft_dirty_enabled(vma) && !pte_soft_dirty(pte);
> > +}
> > +
>
> Should these be "needs" ? I tend to like these names/semantics.

yes. "needs" is better. Glad to know you have the common liking
for these names.

>
>
> >   static inline void vma_iter_config(struct vma_iterator *vmi,
> >               unsigned long index, unsigned long last)
> >   {
> > diff --git a/mm/memory.c b/mm/memory.c
> > index db9130488231..6307c43796aa 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -4322,7 +4322,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> >       if (!folio_test_ksm(folio) &&
> >           (exclusive || folio_ref_count(folio) == 1)) {
> >               if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
> > -                 !vma_soft_dirty_enabled(vma)) {
> > +                 !pte_need_soft_dirty_wp(vma, pte)) {
> >                       pte = pte_mkwrite(pte, vma);
>
> I would move that into a separate patch, as it's not a simple conversion.
>

cool. will separate it in v2.

> --
> Cheers,
>
> David / dhildenb
>

Thanks
Barry