[PATCH v3 40/40] mm/vma: introduce and use vma[_flags]_can_gup()
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Date: 2026-09-17 16:43:31
Also in:
bpf, dri-devel, fuse-devel, kvm, kvm-riscv, kvmarm, linux-arch, linux-doc, linux-fsdevel, linux-mm, linux-perf-users, linux-rdma, linux-riscv, linux-s390, linux-scsi, linux-sound, linux-trace-kernel, linux-usb, linuxppc-dev, lkml, selinux, sparclinux
Subsystem:
filesystems (vfs and infrastructure), hmm - heterogeneous memory management, memory management, memory management - core, memory management - gup (get user pages), memory management - memory policy and migration, the rest · Maintainers:
Alexander Viro, Christian Brauner, Jason Gunthorpe, Leon Romanovsky, Andrew Morton, David Hildenbrand, Linus Torvalds
GUP cannot be used for VMAs which set VMA_IO_BIT - because memory-mapped I/O must not be accessed on the user's behalf - or VMA_PFNMAP_BIT - because PFN maps have no folios which the kernel is permitted to access. Rather than keeping these checks open-coded, abstract them to vma_flags_can_gup() and its VMA wrapper vma_can_gup(). A number of other places make the same check to decide whether a mapping can be populated or accessed as GUP would, so update those too. While here, drop a reference to 'special' and replace a use of the deprecated VMA flags API in vma_dump_size(). No functional change intended. Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> --- fs/coredump.c | 4 ++-- include/linux/mm.h | 29 +++++++++++++++++++++++++++++ mm/gup.c | 7 +++---- mm/hmm.c | 3 +-- mm/memory.c | 14 ++++++++------ mm/mempolicy.c | 3 ++- 6 files changed, 45 insertions(+), 15 deletions(-)
diff --git a/fs/coredump.c b/fs/coredump.c
index fb21fb6703dd..9f729c594c47 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c@@ -1616,8 +1616,8 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma, return 0; } - /* Do not dump I/O mapped devices or special mappings */ - if (vma->vm_flags & VM_IO) + /* Do not dump memory-mapped I/O, which may have side effects on read. */ + if (vma_test(vma, VMA_IO_BIT)) return 0; /* By default, dump shared memory if mapped from an anonymous file. */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5860a3b4dba9..1249e04d7b98 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h@@ -1777,6 +1777,35 @@ static inline bool vma_is_persistent(const struct vm_area_struct *vma) return vma_flags_is_persistent(&vma->flags); } +/** + * vma_flags_can_gup() - Do the specified VMA flags permit GUP to access the + * mapping's pages? + * @flags: The VMA flags to test. + * + * GUP cannot obtain pages from a PFN map (VMA_PFNMAP_BIT), which may have no + * struct pages behind it, and must not provide access to memory-mapped I/O + * (VMA_IO_BIT). + * + * Returns: true if GUP may access pages from the mapping, otherwise false. + */ +static inline bool vma_flags_can_gup(const vma_flags_t *flags) +{ + return !vma_flags_test_any(flags, VMA_IO_BIT, VMA_PFNMAP_BIT); +} + +/** + * vma_can_gup() - May GUP obtain pages from @vma? + * @vma: The VMA to test. + * + * See vma_flags_can_gup() for details. + * + * Returns: true if GUP may access pages from the mapping, otherwise false. + */ +static inline bool vma_can_gup(const struct vm_area_struct *vma) +{ + return vma_flags_can_gup(&vma->flags); +} + /** * vma_kernel_pagesize - Default page size granularity for this VMA. * @vma: The user mapping.
diff --git a/mm/gup.c b/mm/gup.c
index f166acf794e3..8e9ef5ee7498 100644
--- a/mm/gup.c
+++ b/mm/gup.c@@ -1204,7 +1204,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) int foreign = (gup_flags & FOLL_REMOTE); bool vma_anon = vma_is_anonymous(vma); - if (vm_flags & (VM_IO | VM_PFNMAP)) + if (!vma_can_gup(vma)) return -EFAULT; if ((gup_flags & FOLL_ANON) && !vma_anon)
@@ -1955,7 +1955,7 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors) * range with the first VMA. Also, skip undesirable VMA types. */ nend = min(end, vma->vm_end); - if (vma->vm_flags & (VM_IO | VM_PFNMAP)) + if (!vma_can_gup(vma)) continue; if (nstart < vma->vm_start) nstart = vma->vm_start;
@@ -2017,8 +2017,7 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start, break; /* protect what we can, including chardevs */ - if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) || - !(vm_flags & vma->vm_flags)) + if (!vma_can_gup(vma) || !(vm_flags & vma->vm_flags)) break; if (pages) {
diff --git a/mm/hmm.c b/mm/hmm.c
index 2f1e98c6b644..e9569b82a1f0 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c@@ -595,8 +595,7 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end, struct hmm_range *range = hmm_vma_walk->range; struct vm_area_struct *vma = walk->vma; - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)) && - vma->vm_flags & VM_READ) + if (vma_can_gup(vma) && vma_test(vma, VMA_READ_BIT)) return 0; /*
diff --git a/mm/memory.c b/mm/memory.c
index 6c011979401a..338fce99e711 100644
--- a/mm/memory.c
+++ b/mm/memory.c@@ -2417,11 +2417,11 @@ static bool vm_mixed_zeropage_allowed(struct vm_area_struct *vma) * be problematic as soon as the zeropage gets replaced by a different * page due to vma->vm_ops->pfn_mkwrite, because what's mapped would * now differ to what GUP looked up. FSDAX is incompatible to - * FOLL_LONGTERM and VM_IO is incompatible to GUP completely (see - * check_vma_flags). + * FOLL_LONGTERM and memory-mapped I/O is incompatible to GUP completely + * (see vma_can_gup()). */ return vma->vm_ops && vma->vm_ops->pfn_mkwrite && - (vma_is_fsdax(vma) || vma->vm_flags & VM_IO); + (vma_is_fsdax(vma) || vma_test(vma, VMA_IO_BIT)); } static int validate_page_before_insert(struct vm_area_struct *vma,
@@ -7116,7 +7116,8 @@ int follow_pfnmap_start(struct follow_pfnmap_args *args) if (unlikely(address < vma->vm_start || address >= vma->vm_end)) goto out; - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) + /* Only mappings GUP cannot handle are followed here. */ + if (vma_can_gup(vma)) goto out; retry: pgdp = pgd_offset(mm, address);
@@ -7316,8 +7317,9 @@ static int __access_remote_vm(struct mm_struct *mm, unsigned long addr, } /* - * Check if this is a VM_IO | VM_PFNMAP VMA, which - * we can access using slightly different code. + * GUP failed, perhaps because this is a mapping it + * cannot handle (see vma_can_gup()) - such mappings may + * provide access via vm_ops->access() instead. */ bytes = 0; #ifdef CONFIG_HAVE_IOREMAP_PROT
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 044ffb4f4128..2fd759e348ca 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c@@ -2013,7 +2013,8 @@ SYSCALL_DEFINE5(get_mempolicy, int __user *, policy, bool vma_migratable(struct vm_area_struct *vma) { - if (vma->vm_flags & (VM_IO | VM_PFNMAP)) + /* Pages which GUP cannot obtain cannot be migrated either. */ + if (!vma_can_gup(vma)) return false; /*
--
2.55.0