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    Subject[PATCH 02/10] mm: remove write/force parameters from __get_user_pages_unlocked()
    Date
    This patch removes the write and force parameters from
    __get_user_pages_unlocked() to make the use of FOLL_FORCE explicit in callers as
    use of this flag can result in surprising behaviour (and hence bugs) within the
    mm subsystem.

    Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
    ---
    include/linux/mm.h | 3 +--
    mm/gup.c | 17 +++++++++--------
    mm/nommu.c | 12 +++++++++---
    mm/process_vm_access.c | 7 +++++--
    virt/kvm/async_pf.c | 3 ++-
    virt/kvm/kvm_main.c | 11 ++++++++---
    6 files changed, 34 insertions(+), 19 deletions(-)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index e9caec6..2db98b6 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -1285,8 +1285,7 @@ long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
    int write, int force, struct page **pages, int *locked);
    long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
    unsigned long start, unsigned long nr_pages,
    - int write, int force, struct page **pages,
    - unsigned int gup_flags);
    + struct page **pages, unsigned int gup_flags);
    long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
    int write, int force, struct page **pages);
    int get_user_pages_fast(unsigned long start, int nr_pages, int write,
    diff --git a/mm/gup.c b/mm/gup.c
    index ba83942..3d620dd 100644
    --- a/mm/gup.c
    +++ b/mm/gup.c
    @@ -865,17 +865,11 @@ EXPORT_SYMBOL(get_user_pages_locked);
    */
    __always_inline long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
    unsigned long start, unsigned long nr_pages,
    - int write, int force, struct page **pages,
    - unsigned int gup_flags)
    + struct page **pages, unsigned int gup_flags)
    {
    long ret;
    int locked = 1;

    - if (write)
    - gup_flags |= FOLL_WRITE;
    - if (force)
    - gup_flags |= FOLL_FORCE;
    -
    down_read(&mm->mmap_sem);
    ret = __get_user_pages_locked(tsk, mm, start, nr_pages, pages, NULL,
    &locked, false, gup_flags);
    @@ -905,8 +899,15 @@ EXPORT_SYMBOL(__get_user_pages_unlocked);
    long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
    int write, int force, struct page **pages)
    {
    + unsigned int flags = FOLL_TOUCH;
    +
    + if (write)
    + flags |= FOLL_WRITE;
    + if (force)
    + flags |= FOLL_FORCE;
    +
    return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
    - write, force, pages, FOLL_TOUCH);
    + pages, flags);
    }
    EXPORT_SYMBOL(get_user_pages_unlocked);

    diff --git a/mm/nommu.c b/mm/nommu.c
    index 95daf81..925dcc1 100644
    --- a/mm/nommu.c
    +++ b/mm/nommu.c
    @@ -185,8 +185,7 @@ EXPORT_SYMBOL(get_user_pages_locked);

    long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
    unsigned long start, unsigned long nr_pages,
    - int write, int force, struct page **pages,
    - unsigned int gup_flags)
    + struct page **pages, unsigned int gup_flags)
    {
    long ret;
    down_read(&mm->mmap_sem);
    @@ -200,8 +199,15 @@ EXPORT_SYMBOL(__get_user_pages_unlocked);
    long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
    int write, int force, struct page **pages)
    {
    + unsigned int flags = 0;
    +
    + if (write)
    + flags |= FOLL_WRITE;
    + if (force)
    + flags |= FOLL_FORCE;
    +
    return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
    - write, force, pages, 0);
    + pages, flags);
    }
    EXPORT_SYMBOL(get_user_pages_unlocked);

    diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
    index 07514d4..be8dc8d 100644
    --- a/mm/process_vm_access.c
    +++ b/mm/process_vm_access.c
    @@ -88,12 +88,16 @@ static int process_vm_rw_single_vec(unsigned long addr,
    ssize_t rc = 0;
    unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
    / sizeof(struct pages *);
    + unsigned int flags = FOLL_REMOTE;

    /* Work out address and page range required */
    if (len == 0)
    return 0;
    nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;

    + if (vm_write)
    + flags |= FOLL_WRITE;
    +
    while (!rc && nr_pages && iov_iter_count(iter)) {
    int pages = min(nr_pages, max_pages_per_loop);
    size_t bytes;
    @@ -104,8 +108,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
    * current/current->mm
    */
    pages = __get_user_pages_unlocked(task, mm, pa, pages,
    - vm_write, 0, process_pages,
    - FOLL_REMOTE);
    + process_pages, flags);
    if (pages <= 0)
    return -EFAULT;

    diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
    index db96688..8035cc1 100644
    --- a/virt/kvm/async_pf.c
    +++ b/virt/kvm/async_pf.c
    @@ -84,7 +84,8 @@ static void async_pf_execute(struct work_struct *work)
    * mm and might be done in another context, so we must
    * use FOLL_REMOTE.
    */
    - __get_user_pages_unlocked(NULL, mm, addr, 1, 1, 0, NULL, FOLL_REMOTE);
    + __get_user_pages_unlocked(NULL, mm, addr, 1, NULL,
    + FOLL_WRITE | FOLL_REMOTE);

    kvm_async_page_present_sync(vcpu, apf);

    diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    index 81dfc73..28510e7 100644
    --- a/virt/kvm/kvm_main.c
    +++ b/virt/kvm/kvm_main.c
    @@ -1416,10 +1416,15 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
    down_read(&current->mm->mmap_sem);
    npages = get_user_page_nowait(addr, write_fault, page);
    up_read(&current->mm->mmap_sem);
    - } else
    + } else {
    + unsigned int flags = FOLL_TOUCH | FOLL_HWPOISON;
    +
    + if (write_fault)
    + flags |= FOLL_WRITE;
    +
    npages = __get_user_pages_unlocked(current, current->mm, addr, 1,
    - write_fault, 0, page,
    - FOLL_TOUCH|FOLL_HWPOISON);
    + page, flags);
    + }
    if (npages != 1)
    return npages;

    --
    2.10.0
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