[PATCH 4.9 05/38] mm, hugetlbfs: introduce ->split() to vm_operations_struct

Greg Kroah-Hartman
2017-12-04T16:02:45Z

From: Dan Williams <dan.j.williams@intel.com>

commit 31383c6865a578834dd953d9dbc88e6b19fe3997 upstream.

Patch series "device-dax: fix unaligned munmap handling"

When device-dax is operating in huge-page mode we want it to behave like
hugetlbfs and fail attempts to split vmas into unaligned ranges. It
would be messy to teach the munmap path about device-dax alignment
constraints in the same (hstate) way that hugetlbfs communicates this
constraint. Instead, these patches introduce a new ->split() vm
operation.

This patch (of 2):

The device-dax interface has similar constraints as hugetlbfs in that it
requires the munmap path to unmap in huge page aligned units. Rather
than add more custom vma handling code in __split_vma() introduce a new
vm operation to perform this vma specific check.

Link: http://lkml.kernel.org/r/151130418135.4029.6783191281930729710.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/mm.h | 1 +
mm/hugetlb.c | 8 ++++++++
mm/mmap.c | 8 +++++---
3 files changed, 14 insertions(+), 3 deletions(-)

--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -347,6 +347,7 @@ struct fault_env {
struct vm_operations_struct {
void (*open)(struct vm_area_struct * area);
void (*close)(struct vm_area_struct * area);
+ int (*split)(struct vm_area_struct * area, unsigned long addr);
int (*mremap)(struct vm_area_struct * area);
int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
int (*pmd_fault)(struct vm_area_struct *, unsigned long address,
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3135,6 +3135,13 @@ static void hugetlb_vm_op_close(struct v
}
}

+static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
+{
+ if (addr & ~(huge_page_mask(hstate_vma(vma))))
+ return -EINVAL;
+ return 0;
+}
+
/*
* We cannot handle pagefaults against hugetlb pages at all. They cause
* handle_mm_fault() to try to instantiate regular-sized pages in the
@@ -3151,6 +3158,7 @@ const struct vm_operations_struct hugetl
.fault = hugetlb_vm_op_fault,
.open = hugetlb_vm_op_open,
.close = hugetlb_vm_op_close,
+ .split = hugetlb_vm_op_split,
};

static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2538,9 +2538,11 @@ static int __split_vma(struct mm_struct
struct vm_area_struct *new;
int err;

- if (is_vm_hugetlb_page(vma) && (addr &
- ~(huge_page_mask(hstate_vma(vma)))))
- return -EINVAL;
+ if (vma->vm_ops && vma->vm_ops->split) {
+ err = vma->vm_ops->split(vma, addr);
+ if (err)
+ return err;
+ }

new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
if (!new)