[PATCH 5/7] userfaultfd: shmem: add userfaultfd hook for shared memory faults

From: Mike Rapoport
Date: Thu Aug 04 2016 - 06:21:12 EST


When processing a page fault in shared memory area for not present page,
check the VMA determine if faults are to be handled by userfaultfd. If so,
delegate the page fault to handle_userfault.

Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 881b7a0..7ed2a1a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -69,6 +69,7 @@ static struct vfsmount *shm_mnt;
#include <linux/syscalls.h>
#include <linux/fcntl.h>
#include <uapi/linux/memfd.h>
+#include <linux/userfaultfd_k.h>
#include <linux/rmap.h>

#include <asm/uaccess.h>
@@ -123,13 +124,14 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp,
struct shmem_inode_info *info, pgoff_t index);
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
struct page **pagep, enum sgp_type sgp,
- gfp_t gfp, struct mm_struct *fault_mm, int *fault_type);
+ gfp_t gfp, struct vm_area_struct *vma,
+ struct vm_fault *vmf, int *fault_type);

static inline int shmem_getpage(struct inode *inode, pgoff_t index,
struct page **pagep, enum sgp_type sgp)
{
return shmem_getpage_gfp(inode, index, pagep, sgp,
- mapping_gfp_mask(inode->i_mapping), NULL, NULL);
+ mapping_gfp_mask(inode->i_mapping), NULL, NULL, NULL);
}

static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
@@ -1129,7 +1131,7 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp,
*/
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
struct page **pagep, enum sgp_type sgp, gfp_t gfp,
- struct mm_struct *fault_mm, int *fault_type)
+ struct vm_area_struct *vma, struct vm_fault *vmf, int *fault_type)
{
struct address_space *mapping = inode->i_mapping;
struct shmem_inode_info *info;
@@ -1180,7 +1182,7 @@ repeat:
*/
info = SHMEM_I(inode);
sbinfo = SHMEM_SB(inode->i_sb);
- charge_mm = fault_mm ? : current->mm;
+ charge_mm = vma ? vma->vm_mm : current->mm;

if (swap.val) {
/* Look it up and read it in.. */
@@ -1190,7 +1192,8 @@ repeat:
if (fault_type) {
*fault_type |= VM_FAULT_MAJOR;
count_vm_event(PGMAJFAULT);
- mem_cgroup_count_vm_event(fault_mm, PGMAJFAULT);
+ mem_cgroup_count_vm_event(vma->vm_mm,
+ PGMAJFAULT);
}
/* Here we actually start the io */
page = shmem_swapin(swap, gfp, info, index);
@@ -1259,6 +1262,14 @@ repeat:
swap_free(swap);

} else {
+ if (vma && userfaultfd_missing(vma)) {
+ unsigned long addr =
+ (unsigned long)vmf->virtual_address;
+ *fault_type = handle_userfault(vma, addr, vmf->flags,
+ VM_UFFD_MISSING);
+ return 0;
+ }
+
if (shmem_acct_block(info->flags)) {
error = -ENOSPC;
goto failed;
@@ -1432,7 +1443,7 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
}

error = shmem_getpage_gfp(inode, vmf->pgoff, &vmf->page, SGP_CACHE,
- gfp, vma->vm_mm, &ret);
+ gfp, vma, vmf, &ret);
if (error)
return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
return ret;
@@ -3601,7 +3612,7 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,

BUG_ON(mapping->a_ops != &shmem_aops);
error = shmem_getpage_gfp(inode, index, &page, SGP_CACHE,
- gfp, NULL, NULL);
+ gfp, NULL, NULL, NULL);
if (error)
page = ERR_PTR(error);
else
--
1.9.1