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,
--
2.51.0On Mon, Sep 08, 2025 at 12:10:44PM +0100, Lorenzo Stoakes wrote:
> 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;
It would be nicer to have different ops than this, the normal op could
just call the generic helper and then there is only the mixed map op.
Makes me wonder if putting the op in the fops was right, a
mixed/non-mixed vm_ops would do this nicely.
Jason
On Mon, Sep 08, 2025 at 10:27:23AM -0300, Jason Gunthorpe wrote:
> On Mon, Sep 08, 2025 at 12:10:44PM +0100, Lorenzo Stoakes wrote:
> > 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;
>
> It would be nicer to have different ops than this, the normal op could
> just call the generic helper and then there is only the mixed map op.
Right, but I can't stop to refactor everything I change, or this effort will
take even longer.
I do have to compromise a _little_ on that as there's ~250 odd callsites to
go...
>
> Makes me wonder if putting the op in the fops was right, a
> mixed/non-mixed vm_ops would do this nicely.
I added a reviewers note just for you in 00/16 :) I guess you missed it:
REVIEWER NOTE:
~~~~~~~~~~~~~~
I considered putting the complete, abort callbacks in vm_ops,
however this won't work because then we would be unable to adjust
helpers like ngeneric_file_mmap_prepare() (which provides vm_ops)
to provide the correct complete, abort callbacks.
Conceptually it also makes more sense to have these in f_op as they
are one-off operations performed at mmap time to establish the VMA,
rather than a property of the VMA itself.
Basically, existing generic code sets vm_ops to something already, now we'd
need to somehow also vary it on this as well or nest vm_ops? I don't think
it's workable.
I found this out because I started working on this series with the complete
callback as part of vm_ops then hit this stumbling block as a result.
>
> Jason
Cheers, Lorenzo
© 2016 - 2025 Red Hat, Inc.