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    Subject[PATCH v3 06/12] Add get_user_pages() variant that fails if major fault is required.
    Date
    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@redhat.com>
    Signed-off-by: Gleb Natapov <gleb@redhat.com>
    ---
    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 15458de..338527e 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 2265f28..32e9c6e 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -136,6 +136,7 @@ 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
    @@ -836,6 +837,9 @@ 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);
    @@ -1257,6 +1261,7 @@ 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 96ac6b0..25768ad 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -1509,6 +1509,9 @@ 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 09e4b1b..89e0074 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -1336,10 +1336,13 @@ 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)
    @@ -1347,6 +1350,8 @@ 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)
    @@ -1457,6 +1462,23 @@ 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
    @@ -2536,6 +2558,9 @@ 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 eef4ebe..ab3a255 100644
    --- a/mm/shmem.c
    +++ b/mm/shmem.c
    @@ -1225,6 +1225,7 @@ 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;
    @@ -1273,6 +1274,11 @@ 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);
    @@ -1481,7 +1487,7 @@ 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;
    --
    1.6.5


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