[PATCH v4 02/20] mm: provide vma_[flags_]is_cow_mapping() and remove is_cow_mapping()
From: Lorenzo Stoakes (ARM)
Date: Thu Aug 06 2026 - 16:28:37 EST
All remaining callers of is_cow_mapping() are invoking it in the form of
is_cow_mapping(vma->vm_flags) or an indirected version of this.
Therefore, provide a helper - vma_is_cow_mapping() to directly test the
VMA.
Additionally provide a new helper vma_flags_is_cow_mapping() which performs
the check using the new vma_flags_t type, and share this logic between
vma_is_cow_mapping() and vma_desc_is_cow_mapping().
With these changes, no callers of is_cow_mapping() remain, so remove it.
Also update the userland VMA tests to reflect the change.
No functional change intended.
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
---
arch/s390/mm/gmap_helpers.c | 2 +-
drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 4 ++--
drivers/gpu/drm/drm_gem_shmem_helper.c | 2 +-
drivers/gpu/drm/panthor/panthor_gem.c | 2 +-
drivers/gpu/drm/ttm/ttm_bo_vm.c | 2 +-
drivers/gpu/drm/xe/xe_device.c | 2 +-
fs/proc/task_mmu.c | 2 +-
include/linux/mm.h | 15 +++++++++------
kernel/events/uprobes.c | 2 +-
mm/gup.c | 2 +-
mm/huge_memory.c | 8 ++++----
mm/hugetlb.c | 2 +-
mm/internal.h | 2 +-
mm/memory.c | 25 ++++++++++++-------------
mm/mempolicy.c | 2 +-
tools/testing/vma/include/dup.h | 11 +++++++++++
16 files changed, 49 insertions(+), 36 deletions(-)
diff --git a/arch/s390/mm/gmap_helpers.c b/arch/s390/mm/gmap_helpers.c
index 4bf7c9012feb..cd5fded159c0 100644
--- a/arch/s390/mm/gmap_helpers.c
+++ b/arch/s390/mm/gmap_helpers.c
@@ -200,7 +200,7 @@ static int find_zeropage_pte_entry(pte_t *pte, unsigned long addr,
* currently only works in COW mappings, which is also where
* mm_forbids_zeropage() is checked.
*/
- if (!is_cow_mapping(walk->vma->vm_flags))
+ if (!vma_is_cow_mapping(walk->vma))
return -EFAULT;
*found_addr = addr;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
index 6a0699746fbc..0c7309080a7a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
@@ -377,9 +377,9 @@ static int amdgpu_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_str
/* Workaround for Thunk bug creating PROT_NONE,MAP_PRIVATE mappings
* for debugger access to invisible VRAM. Should have used MAP_SHARED
* instead. Clearing VM_MAYWRITE prevents the mapping from ever
- * becoming writable and makes is_cow_mapping(vm_flags) false.
+ * becoming writable and makes vma_is_cow_mapping(vma) false.
*/
- if (is_cow_mapping(vma->vm_flags) &&
+ if (vma_is_cow_mapping(vma) &&
!(vma->vm_flags & VM_ACCESS_FLAGS))
vm_flags_clear(vma, VM_MAYWRITE);
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 06d019d51d3e..177d0e0b9334 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -753,7 +753,7 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
return ret;
}
- if (is_cow_mapping(vma->vm_flags))
+ if (vma_is_cow_mapping(vma))
return -EINVAL;
dma_resv_lock(shmem->base.resv, NULL);
diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index 770556353968..d2eec46f7abe 100644
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -761,7 +761,7 @@ static int panthor_gem_mmap(struct drm_gem_object *obj, struct vm_area_struct *v
return ret;
}
- if (is_cow_mapping(vma->vm_flags))
+ if (vma_is_cow_mapping(vma))
return -EINVAL;
if (!refcount_inc_not_zero(&bo->cmap.mmap_count)) {
diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 88babf435ac2..872bf444b1f0 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -489,7 +489,7 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
{
/* Enforce no COW since would have really strange behavior with it. */
- if (is_cow_mapping(vma->vm_flags))
+ if (vma_is_cow_mapping(vma))
return -EINVAL;
drm_gem_object_get(&bo->base);
diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index 838797cc65d7..ab16937ebbe0 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -330,7 +330,7 @@ static int xe_pci_barrier_mmap(struct file *filp,
if (vma->vm_end - vma->vm_start > SZ_4K)
return -EINVAL;
- if (is_cow_mapping(vma->vm_flags))
+ if (vma_is_cow_mapping(vma))
return -EINVAL;
if (vma->vm_flags & (VM_READ | VM_EXEC))
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 817e3e0f9194..5c54aebe2118 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1693,7 +1693,7 @@ static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr,
if (!pte_write(pte))
return false;
- if (!is_cow_mapping(vma->vm_flags))
+ if (!vma_is_cow_mapping(vma))
return false;
if (likely(!mm_flags_test(MMF_HAS_PINNED, vma->vm_mm)))
return false;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index df78847f5f07..a3368c542947 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2271,17 +2271,20 @@ void unpin_user_pages(struct page **pages, unsigned long npages);
void unpin_user_folio(struct folio *folio, unsigned long npages);
void unpin_folios(struct folio **folios, unsigned long nfolios);
-static inline bool is_cow_mapping(vm_flags_t flags)
+static inline bool vma_flags_is_cow_mapping(const vma_flags_t *flags)
{
- return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
+ return vma_flags_test(flags, VMA_MAYWRITE_BIT) &&
+ !vma_flags_test(flags, VMA_SHARED_BIT);
}
-static inline bool vma_desc_is_cow_mapping(struct vm_area_desc *desc)
+static inline bool vma_is_cow_mapping(const struct vm_area_struct *vma)
{
- const vma_flags_t *flags = &desc->vma_flags;
+ return vma_flags_is_cow_mapping(&vma->flags);
+}
- return vma_flags_test(flags, VMA_MAYWRITE_BIT) &&
- !vma_flags_test(flags, VMA_SHARED_BIT);
+static inline bool vma_desc_is_cow_mapping(struct vm_area_desc *desc)
+{
+ return vma_flags_is_cow_mapping(&desc->vma_flags);
}
#ifndef CONFIG_MMU
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ae2f3b9f8d50..eb0d11092fb3 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -513,7 +513,7 @@ int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
uprobe = container_of(auprobe, struct uprobe, arch);
- if (WARN_ON_ONCE(!is_cow_mapping(vma->vm_flags)))
+ if (WARN_ON_ONCE(!vma_is_cow_mapping(vma)))
return -EINVAL;
/*
diff --git a/mm/gup.c b/mm/gup.c
index 1d32e9a3dc79..b534ef58c46a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1236,7 +1236,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
* Anon pages in shared mappings are surprising: now
* just reject it.
*/
- if (!is_cow_mapping(vm_flags))
+ if (!vma_is_cow_mapping(vma))
return -EFAULT;
}
} else if (!(vm_flags & VM_READ)) {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9b1f3b24f7e0..6b0cabd45b2d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1638,7 +1638,7 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, unsigned long pfn,
BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
(VM_PFNMAP|VM_MIXEDMAP));
- BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
+ BUG_ON((vma->vm_flags & VM_PFNMAP) && vma_is_cow_mapping(vma));
pfnmap_setup_cachemode_pfn(pfn, &pgprot);
@@ -1746,7 +1746,7 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, unsigned long pfn,
BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
(VM_PFNMAP|VM_MIXEDMAP));
- BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
+ BUG_ON((vma->vm_flags & VM_PFNMAP) && vma_is_cow_mapping(vma));
pfnmap_setup_cachemode_pfn(pfn, &pgprot);
@@ -1888,7 +1888,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* applied special bit, or we made the PRIVATE mapping be
* able to wrongly write to the backend MMIO.
*/
- VM_WARN_ON_ONCE(is_cow_mapping(src_vma->vm_flags) && pmd_write(pmd));
+ VM_WARN_ON_ONCE(vma_is_cow_mapping(src_vma) && pmd_write(pmd));
goto set_pmd;
}
@@ -2009,7 +2009,7 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* TODO: once we support anonymous pages, use
* folio_try_dup_anon_rmap_*() and split if duplicating fails.
*/
- if (is_cow_mapping(vma->vm_flags) && pud_write(pud)) {
+ if (vma_is_cow_mapping(vma) && pud_write(pud)) {
pudp_set_wrprotect(src_mm, addr, src_pud);
pud = pud_wrprotect(pud);
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d86a27c8819c..560e85ca1d1c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4905,7 +4905,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
pte_t *src_pte, *dst_pte, entry;
struct folio *pte_folio;
unsigned long addr;
- bool cow = is_cow_mapping(src_vma->vm_flags);
+ bool cow = vma_is_cow_mapping(src_vma);
struct hstate *h = hstate_vma(src_vma);
unsigned long sz = huge_page_size(h);
unsigned long npages = pages_per_huge_page(h);
diff --git a/mm/internal.h b/mm/internal.h
index f26423de4ca2..a75a1344e9ba 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1341,7 +1341,7 @@ static inline bool gup_must_unshare(struct vm_area_struct *vma,
* ... because we only care about writable private ("COW")
* mappings where we have to break COW early.
*/
- return is_cow_mapping(vma->vm_flags);
+ return vma_is_cow_mapping(vma);
}
/* Paired with a memory barrier in folio_try_share_anon_rmap_*(). */
diff --git a/mm/memory.c b/mm/memory.c
index d5e87624f692..e1349e18f046 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -780,7 +780,7 @@ static inline struct page *__vm_normal_page(struct vm_area_struct *vma,
/* Only CoW'ed anon folios are "normal". */
if (pfn == index)
return NULL;
- if (!is_cow_mapping(vma->vm_flags))
+ if (!vma_is_cow_mapping(vma))
return NULL;
}
}
@@ -1002,7 +1002,6 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *dst_vma,
struct vm_area_struct *src_vma, unsigned long addr, int *rss)
{
- vm_flags_t vm_flags = dst_vma->vm_flags;
pte_t orig_pte = ptep_get(src_pte);
softleaf_t entry = softleaf_from_pte(orig_pte);
pte_t pte = orig_pte;
@@ -1026,7 +1025,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
rss[mm_counter(folio)]++;
if (!softleaf_is_migration_read(entry) &&
- is_cow_mapping(vm_flags)) {
+ vma_is_cow_mapping(dst_vma)) {
/*
* COW mappings require pages in both parent and child
* to be set to read. A previously exclusive entry is
@@ -1067,7 +1066,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* save and restore device driver state).
*/
if (softleaf_is_device_private_write(entry) &&
- is_cow_mapping(vm_flags)) {
+ vma_is_cow_mapping(dst_vma)) {
entry = make_readable_device_private_entry(
swp_offset(entry));
pte = swp_entry_to_pte(entry);
@@ -1082,7 +1081,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* exclusive entries currently only support private writable
* (ie. COW) mappings.
*/
- VM_BUG_ON(!is_cow_mapping(src_vma->vm_flags));
+ VM_BUG_ON(!vma_is_cow_mapping(src_vma));
if (try_restore_exclusive_pte(src_vma, addr, src_pte, orig_pte))
return -EBUSY;
return -ENOENT;
@@ -1181,7 +1180,7 @@ static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma,
}
/* If it's a COW mapping, write protect it both processes. */
- if (is_cow_mapping(src_vma->vm_flags) && writable) {
+ if (vma_is_cow_mapping(src_vma) && writable) {
wrprotect_ptes(src_mm, addr, src_pte, nr);
pte = pte_wrprotect(pte);
}
@@ -1602,9 +1601,9 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
* We need to invalidate the secondary MMU mappings only when
* there could be a permission downgrade on the ptes of the
* parent mm. And a permission downgrade will only happen if
- * is_cow_mapping() returns true.
+ * vma_is_cow_mapping() returns true.
*/
- is_cow = is_cow_mapping(src_vma->vm_flags);
+ is_cow = vma_is_cow_mapping(src_vma);
if (is_cow) {
mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE,
@@ -2388,7 +2387,7 @@ static bool vm_mixed_zeropage_allowed(struct vm_area_struct *vma)
if (mm_forbids_zeropage(vma->vm_mm))
return false;
/* zeropages in COW mappings are common and unproblematic. */
- if (is_cow_mapping(vma->vm_flags))
+ if (vma_is_cow_mapping(vma))
return true;
/* Mappings that do not allow for writable PTEs are unproblematic. */
if (!(vma->vm_flags & (VM_WRITE | VM_MAYWRITE)))
@@ -2839,7 +2838,7 @@ vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
(VM_PFNMAP|VM_MIXEDMAP));
- BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
+ BUG_ON((vma->vm_flags & VM_PFNMAP) && vma_is_cow_mapping(vma));
BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
if (addr < vma->vm_start || addr >= vma->vm_end)
@@ -3251,7 +3250,7 @@ static int remap_pfn_range_prepare_vma(struct vm_area_struct *vma,
unsigned long size)
{
const unsigned long end = addr + PAGE_ALIGN(size);
- const bool is_cow = is_cow_mapping(vma->vm_flags);
+ const bool is_cow = vma_is_cow_mapping(vma);
int err;
err = get_remap_pgoff(is_cow, addr, end, vma->vm_start, vma->vm_end,
@@ -6751,7 +6750,7 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
* FAULT_FLAG_UNSHARE only applies to COW mappings. Let's
* just treat it like an ordinary read-fault otherwise.
*/
- if (!is_cow_mapping(vma->vm_flags))
+ if (!vma_is_cow_mapping(vma))
*flags &= ~FAULT_FLAG_UNSHARE;
} else if (*flags & FAULT_FLAG_WRITE) {
/* Write faults on read-only mappings are impossible ... */
@@ -6759,7 +6758,7 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
return VM_FAULT_SIGSEGV;
/* ... and FOLL_FORCE only applies to COW mappings. */
if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE) &&
- !is_cow_mapping(vma->vm_flags)))
+ !vma_is_cow_mapping(vma)))
return VM_FAULT_SIGSEGV;
}
#ifdef CONFIG_PER_VMA_LOCK
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 5720f7f54d94..3498a5651d50 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -844,7 +844,7 @@ bool folio_can_map_prot_numa(struct folio *folio, struct vm_area_struct *vma,
return false;
/* Also skip shared copy-on-write folios */
- if (is_cow_mapping(vma->vm_flags) && folio_maybe_mapped_shared(folio))
+ if (vma_is_cow_mapping(vma) && folio_maybe_mapped_shared(folio))
return false;
/* Folios are pinned and can't be migrated */
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 26d9210b1e8b..40ad83936b28 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -1162,6 +1162,17 @@ static inline bool vma_is_shared_maywrite(struct vm_area_struct *vma)
return is_shared_maywrite(&vma->flags);
}
+static inline bool vma_flags_is_cow_mapping(const vma_flags_t *flags)
+{
+ return vma_flags_test(flags, VMA_MAYWRITE_BIT) &&
+ !vma_flags_test(flags, VMA_SHARED_BIT);
+}
+
+static inline bool vma_is_cow_mapping(const struct vm_area_struct *vma)
+{
+ return vma_flags_is_cow_mapping(&vma->flags);
+}
+
static inline struct vm_area_struct *vma_next(struct vma_iterator *vmi)
{
/*
--
2.55.0