mm, hugetlbfs: introduce ->split() to vm_operations_struct

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ee073146aaa7c0085d4e212726be5d60ee317e5a..b3b6a7e313e947d9db18855e21b6d624419e7f8d 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -377,6 +377,7 @@ enum page_entry_size {
 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_fault *vmf);
        int (*huge_fault)(struct vm_fault *vmf, enum page_entry_size pe_size);

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 681b300185c0c0383bb240d6a898849bf777f46b..698e8fb340318664c591f7ba787b15b58add64cb 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3125,6 +3125,13 @@ static void hugetlb_vm_op_close(struct vm_area_struct *vma)
        }
 }
 
+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
@@ -3141,6 +3148,7 @@ const struct vm_operations_struct hugetlb_vm_ops = {
        .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,

diff --git a/mm/mmap.c b/mm/mmap.c
index 924839fac0e6421a77839825a99833a342d3153c..a4d5468212149db8a4cf20f9917c7bf48231a9ce 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2555,9 +2555,11 @@ int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
        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)