[PATCH v4 06/12] Add get_user_pages() variant that fails if major fault is required.

From: Gleb Natapov
Date: Tue Jul 06 2010 - 12:25:50 EST

This patch add get_user_pages() variant that only succeeds if getting
a reference to a page doesn't require major fault.

Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
---
fs/ncpfs/mmap.c | 2 ++
include/linux/mm.h | 5 +++++
mm/filemap.c | 3 +++
mm/memory.c | 31 ++++++++++++++++++++++++++++---
mm/shmem.c | 8 +++++++-
5 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/fs/ncpfs/mmap.c b/fs/ncpfs/mmap.c
index 56f5b3a..b9c4f36 100644
--- a/fs/ncpfs/mmap.c
+++ b/fs/ncpfs/mmap.c
@@ -39,6 +39,8 @@ static int ncp_file_mmap_fault(struct vm_area_struct *area,
int bufsize;
int pos; /* XXX: loff_t ? */

+ if (vmf->flags & FAULT_FLAG_MINOR)
+ return VM_FAULT_MAJOR | VM_FAULT_ERROR;
/*
* ncpfs has nothing against high pages as long
* as recvmsg and memset works on it
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4238a9c..2bfc85a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -140,6 +140,7 @@ extern pgprot_t protection_map[16];
#define FAULT_FLAG_WRITE 0x01 /* Fault was a write access */
#define FAULT_FLAG_NONLINEAR 0x02 /* Fault was via a nonlinear mapping */
#define FAULT_FLAG_MKWRITE 0x04 /* Fault was mkwrite of existing pte */
+#define FAULT_FLAG_MINOR 0x08 /* Do only minor fault */

/*
* This interface is used by x86 PAT code to identify a pfn mapping that is
@@ -843,6 +844,9 @@ extern int access_process_vm(struct task_struct *tsk, unsigned long addr, void *
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int nr_pages, int write, int force,
struct page **pages, struct vm_area_struct **vmas);
+int get_user_pages_noio(struct task_struct *tsk, struct mm_struct *mm,
+ unsigned long start, int nr_pages, int write, int force,
+ struct page **pages, struct vm_area_struct **vmas);
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages);
struct page *get_dump_page(unsigned long addr);
@@ -1373,6 +1377,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address,
#define FOLL_GET 0x04 /* do get_page on page */
#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */
#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
+#define FOLL_MINOR 0x20 /* do only minor page faults */

typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
void *data);
diff --git a/mm/filemap.c b/mm/filemap.c
index 20e5642..1186338 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1548,6 +1548,9 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
goto no_cached_page;
}
} else {
+ if (vmf->flags & FAULT_FLAG_MINOR)
+ return VM_FAULT_MAJOR | VM_FAULT_ERROR;
+
/* No page in the page cache at all */
do_sync_mmap_readahead(vma, ra, file, offset);
count_vm_event(PGMAJFAULT);
diff --git a/mm/memory.c b/mm/memory.c
index 119b7cc..7dfaba2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1433,10 +1433,13 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
cond_resched();
while (!(page = follow_page(vma, start, foll_flags))) {
int ret;
+ unsigned int fault_fl =
+ ((foll_flags & FOLL_WRITE) ?
+ FAULT_FLAG_WRITE : 0) |
+ ((foll_flags & FOLL_MINOR) ?
+ FAULT_FLAG_MINOR : 0);

- ret = handle_mm_fault(mm, vma, start,
- (foll_flags & FOLL_WRITE) ?
- FAULT_FLAG_WRITE : 0);
+ ret = handle_mm_fault(mm, vma, start, fault_fl);

if (ret & VM_FAULT_ERROR) {
if (ret & VM_FAULT_OOM)
@@ -1444,6 +1447,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
if (ret &
(VM_FAULT_HWPOISON|VM_FAULT_SIGBUS))
return i ? i : -EFAULT;
+ else if (ret & VM_FAULT_MAJOR)
+ return i ? i : -EFAULT;
BUG();
}
if (ret & VM_FAULT_MAJOR)
@@ -1554,6 +1559,23 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
}
EXPORT_SYMBOL(get_user_pages);

+int get_user_pages_noio(struct task_struct *tsk, struct mm_struct *mm,
+ unsigned long start, int nr_pages, int write, int force,
+ struct page **pages, struct vm_area_struct **vmas)
+{
+ int flags = FOLL_TOUCH | FOLL_MINOR;
+
+ if (pages)
+ flags |= FOLL_GET;
+ if (write)
+ flags |= FOLL_WRITE;
+ if (force)
+ flags |= FOLL_FORCE;
+
+ return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas);
+}
+EXPORT_SYMBOL(get_user_pages_noio);
+
/**
* get_dump_page() - pin user page in memory while writing it to core dump
* @addr: user address
@@ -2640,6 +2662,9 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
delayacct_set_flag(DELAYACCT_PF_SWAPIN);
page = lookup_swap_cache(entry);
if (!page) {
+ if (flags & FAULT_FLAG_MINOR)
+ return VM_FAULT_MAJOR | VM_FAULT_ERROR;
+
grab_swap_token(mm); /* Contend for token _before_ read-in */
page = swapin_readahead(entry,
GFP_HIGHUSER_MOVABLE, vma, address);
diff --git a/mm/shmem.c b/mm/shmem.c
index f65f840..acc8958 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1227,6 +1227,7 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
swp_entry_t swap;
gfp_t gfp;
int error;
+ int flags = type ? *type : 0;

if (idx >= SHMEM_MAX_INDEX)
return -EFBIG;
@@ -1275,6 +1276,11 @@ repeat:
swappage = lookup_swap_cache(swap);
if (!swappage) {
shmem_swp_unmap(entry);
+ if (flags & FAULT_FLAG_MINOR) {
+ spin_unlock(&info->lock);
+ *type = VM_FAULT_MAJOR | VM_FAULT_ERROR;
+ goto failed;
+ }
/* here we actually do the io */
if (type && !(*type & VM_FAULT_MAJOR)) {
__count_vm_event(PGMAJFAULT);
@@ -1483,7 +1489,7 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
int error;
- int ret;
+ int ret = (int)vmf->flags;

if (((loff_t)vmf->pgoff << PAGE_CACHE_SHIFT) >= i_size_read(inode))
return VM_FAULT_SIGBUS;
--
1.7.1

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