[PATCH 13/16] mm: update cramfs to use mmap_prepare, mmap_complete

Lorenzo Stoakes
2025-09-08T11:12:38Z

We thread the state through the mmap_context, allowing for both PFN map and
mixed mapped pre-population.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
fs/cramfs/inode.c | 134 +++++++++++++++++++++++++++++++---------------
1 file changed, 92 insertions(+), 42 deletions(-)

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index b002e9b734f9..11a11213304d 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -59,6 +59,12 @@ static const struct address_space_operations cramfs_aops;

static DEFINE_MUTEX(read_mutex);

+/* How should the mapping be completed? */
+enum cramfs_mmap_state {
+ NO_PREPOPULATE,
+ PREPOPULATE_PFNMAP,
+ PREPOPULATE_MIXEDMAP,
+};

/* These macros may change in future, to provide better st_ino semantics. */
#define OFFSET(x) ((x)->i_ino)
@@ -342,34 +348,89 @@ static bool cramfs_last_page_is_shared(struct inode *inode)
return memchr_inv(tail_data, 0, PAGE_SIZE - partial) ? true : false;
}

-static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma)
+static int cramfs_physmem_mmap_complete(struct file *file, struct vm_area_struct *vma,
+ const void *context)
{
struct inode *inode = file_inode(file);
struct cramfs_sb_info *sbi = CRAMFS_SB(inode->i_sb);
- unsigned int pages, max_pages, offset;
unsigned long address, pgoff = vma->vm_pgoff;
- char *bailout_reason;
- int ret;
+ unsigned int pages, offset;
+ enum cramfs_mmap_state mmap_state = (enum cramfs_mmap_state)context;
+ int ret = 0;

- ret = generic_file_readonly_mmap(file, vma);
- if (ret)
- return ret;
+ if (mmap_state == NO_PREPOPULATE)
+ return 0;
+
+ offset = cramfs_get_block_range(inode, pgoff, &pages);
+ address = sbi->linear_phys_addr + offset;

/*
* Now try to pre-populate ptes for this vma with a direct
* mapping avoiding memory allocation when possible.
*/

+ if (mmap_state == PREPOPULATE_PFNMAP) {
+ /*
+ * The entire vma is mappable. remap_pfn_range() will
+ * make it distinguishable from a non-direct mapping
+ * in /proc/<pid>/maps by substituting the file offset
+ * with the actual physical address.
+ */
+ ret = remap_pfn_range_complete(vma, vma->vm_start, address >> PAGE_SHIFT,
+ pages * PAGE_SIZE, vma->vm_page_prot);
+ } else {
+ /*
+ * Let's create a mixed map if we can't map it all.
+ * The normal paging machinery will take care of the
+ * unpopulated ptes via cramfs_read_folio().
+ */
+ int i;
+
+ for (i = 0; i < pages && !ret; i++) {
+ vm_fault_t vmf;
+ unsigned long off = i * PAGE_SIZE;
+
+ vmf = vmf_insert_mixed(vma, vma->vm_start + off,
+ address + off);
+ if (vmf & VM_FAULT_ERROR)
+ ret = vm_fault_to_errno(vmf, 0);
+ }
+ }
+
+ if (!ret)
+ pr_debug("mapped %pD[%lu] at 0x%08lx (%u/%lu pages) "
+ "to vma 0x%08lx, page_prot 0x%llx\n", file,
+ pgoff, address, pages, vma_pages(vma), vma->vm_start,
+ (unsigned long long)pgprot_val(vma->vm_page_prot));
+ return ret;
+}
+
+static int cramfs_physmem_mmap_prepare(struct vm_area_desc *desc)
+{
+ struct file *file = desc->file;
+ struct inode *inode = file_inode(file);
+ struct cramfs_sb_info *sbi = CRAMFS_SB(inode->i_sb);
+ unsigned int pages, max_pages, offset, mapped_pages;
+ unsigned long address, pgoff = desc->pgoff;
+ enum cramfs_mmap_state mmap_state;
+ char *bailout_reason;
+ int ret;
+
+ ret = generic_file_readonly_mmap_prepare(desc);
+ if (ret)
+ return ret;
+
/* Could COW work here? */
bailout_reason = "vma is writable";
- if (vma->vm_flags & VM_WRITE)
+ if (desc->vm_flags & VM_WRITE)
goto bailout;

max_pages = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
bailout_reason = "beyond file limit";
if (pgoff >= max_pages)
goto bailout;
- pages = min(vma_pages(vma), max_pages - pgoff);
+ mapped_pages = vma_desc_pages(desc);
+ pages = min(mapped_pages, max_pages - pgoff);

offset = cramfs_get_block_range(inode, pgoff, &pages);
bailout_reason = "unsuitable block layout";
@@ -391,41 +452,23 @@ static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma)
goto bailout;
}

- if (pages == vma_pages(vma)) {
- /*
- * The entire vma is mappable. remap_pfn_range() will
- * make it distinguishable from a non-direct mapping
- * in /proc/<pid>/maps by substituting the file offset
- * with the actual physical address.
- */
- ret = remap_pfn_range(vma, vma->vm_start, address >> PAGE_SHIFT,
- pages * PAGE_SIZE, vma->vm_page_prot);
+ if (mapped_pages == pages)
+ mmap_state = PREPOPULATE_PFNMAP;
+ else
+ mmap_state = PREPOPULATE_MIXEDMAP;
+ desc->mmap_context = (void *)mmap_state;
+
+ if (mmap_state == PREPOPULATE_PFNMAP) {
+ /* No CoW allowed, so no need to provide PFN. */
+ remap_pfn_range_prepare(desc, 0);
} else {
- /*
- * Let's create a mixed map if we can't map it all.
- * The normal paging machinery will take care of the
- * unpopulated ptes via cramfs_read_folio().
- */
- int i;
- vm_flags_set(vma, VM_MIXEDMAP);
- for (i = 0; i < pages && !ret; i++) {
- vm_fault_t vmf;
- unsigned long off = i * PAGE_SIZE;
- vmf = vmf_insert_mixed(vma, vma->vm_start + off,
- address + off);
- if (vmf & VM_FAULT_ERROR)
- ret = vm_fault_to_errno(vmf, 0);
- }
+ desc->vm_flags |= VM_MIXEDMAP;
}

- if (!ret)
- pr_debug("mapped %pD[%lu] at 0x%08lx (%u/%lu pages) "
- "to vma 0x%08lx, page_prot 0x%llx\n", file,
- pgoff, address, pages, vma_pages(vma), vma->vm_start,
- (unsigned long long)pgprot_val(vma->vm_page_prot));
- return ret;
+ return 0;

bailout:
+ desc->mmap_context = (void *)NO_PREPOPULATE;
pr_debug("%pD[%lu]: direct mmap impossible: %s\n",
file, pgoff, bailout_reason);
/* Didn't manage any direct map, but normal paging is still possible */
@@ -434,9 +477,15 @@ static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma)

#else /* CONFIG_MMU */

-static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma)
+static int cramfs_physmem_mmap_prepare(struct vm_area_desc *desc)
{
- return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -ENOSYS;
+ return is_nommu_shared_mapping(desc->vm_flags) ? 0 : -ENOSYS;
+}
+
+static int cramfs_physmem_mmap_complete(struct file *file,
+ struct vm_area_struct *vma)
+{
+ return 0;
}

static unsigned long cramfs_physmem_get_unmapped_area(struct file *file,
@@ -474,7 +523,8 @@ static const struct file_operations cramfs_physmem_fops = {
.llseek = generic_file_llseek,
.read_iter = generic_file_read_iter,
.splice_read = filemap_splice_read,
- .mmap = cramfs_physmem_mmap,
+ .mmap_prepare = cramfs_physmem_mmap_prepare,
+ .mmap_complete = cramfs_physmem_mmap_complete,
#ifndef CONFIG_MMU
.get_unmapped_area = cramfs_physmem_get_unmapped_area,
.mmap_capabilities = cramfs_physmem_mmap_capabilities,
--
2.51.0