Re: [PATCH v3 40/40] mm/vma: introduce and use vma[_flags]_can_gup()

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);
+}

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));

 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;