Re: [PATCH 2/2] mm: unexport __get_user_pages_unlocked()

From: Michal Hocko
Date: Thu Oct 27 2016 - 11:14:50 EST

On Thu 27-10-16 10:51:41, Lorenzo Stoakes wrote:
> This patch unexports the low-level __get_user_pages_unlocked() function and
> replaces invocations with calls to more appropriate higher-level functions.
>
> In hva_to_pfn_slow() we are able to replace __get_user_pages_unlocked() with
> get_user_pages_unlocked() since we can now pass gup_flags.
>
> In async_pf_execute() and process_vm_rw_single_vec() we need to pass different
> tsk, mm arguments so get_user_pages_remote() is the sane replacement in these
> cases (having added manual acquisition and release of mmap_sem.)
>
> Additionally get_user_pages_remote() reintroduces use of the FOLL_TOUCH
> flag. However, this flag was originally silently dropped by 1e9877902dc7e
> ("mm/gup: Introduce get_user_pages_remote()"), so this appears to have been
> unintentional and reintroducing it is therefore not an issue.

Looks good to me.

> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
> include/linux/mm.h | 3 ---
> mm/gup.c | 8 ++++----
> mm/nommu.c | 7 +++----
> mm/process_vm_access.c | 12 ++++++++----
> virt/kvm/async_pf.c | 10 +++++++---
> virt/kvm/kvm_main.c | 5 ++---
> 6 files changed, 24 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index cc15445..7b2d14e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1280,9 +1280,6 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
> struct vm_area_struct **vmas);
> long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
> unsigned int gup_flags, 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,
> - struct page **pages, unsigned int gup_flags);
> long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> struct page **pages, unsigned int gup_flags);
> int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> diff --git a/mm/gup.c b/mm/gup.c
> index 0567851..8028af1 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -866,9 +866,10 @@ EXPORT_SYMBOL(get_user_pages_locked);
> * caller if required (just like with __get_user_pages). "FOLL_GET"
> * is set implicitly if "pages" is non-NULL.
> */
> -__always_inline long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
> - unsigned long start, unsigned long nr_pages,
> - struct page **pages, unsigned int gup_flags)
> +static __always_inline long __get_user_pages_unlocked(struct task_struct *tsk,
> + struct mm_struct *mm, unsigned long start,
> + unsigned long nr_pages, struct page **pages,
> + unsigned int gup_flags)
> {
> long ret;
> int locked = 1;
> @@ -880,7 +881,6 @@ __always_inline long __get_user_pages_unlocked(struct task_struct *tsk, struct m
> up_read(&mm->mmap_sem);
> return ret;
> }
> -EXPORT_SYMBOL(__get_user_pages_unlocked);
>
> /*
> * get_user_pages_unlocked() is suitable to replace the form:
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 8b8faaf..669437b 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -176,9 +176,9 @@ long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
> }
> 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,
> - struct page **pages, unsigned int gup_flags)
> +static long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
> + unsigned long start, unsigned long nr_pages,
> + struct page **pages, unsigned int gup_flags)
> {
> long ret;
> down_read(&mm->mmap_sem);
> @@ -187,7 +187,6 @@ long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
> up_read(&mm->mmap_sem);
> return ret;
> }
> -EXPORT_SYMBOL(__get_user_pages_unlocked);
>
> long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> struct page **pages, unsigned int gup_flags)
> diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
> index be8dc8d..84d0c7e 100644
> --- a/mm/process_vm_access.c
> +++ b/mm/process_vm_access.c
> @@ -88,7 +88,7 @@ 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;
> + unsigned int flags = 0;
>
> /* Work out address and page range required */
> if (len == 0)
> @@ -100,15 +100,19 @@ static int process_vm_rw_single_vec(unsigned long addr,
>
> while (!rc && nr_pages && iov_iter_count(iter)) {
> int pages = min(nr_pages, max_pages_per_loop);
> + int locked = 1;
> size_t bytes;
>
> /*
> * Get the pages we're interested in. We must
> - * add FOLL_REMOTE because task/mm might not
> + * access remotely because task/mm might not
> * current/current->mm
> */
> - pages = __get_user_pages_unlocked(task, mm, pa, pages,
> - process_pages, flags);
> + down_read(&mm->mmap_sem);
> + pages = get_user_pages_remote(task, mm, pa, pages, flags,
> + process_pages, NULL, &locked);
> + if (locked)
> + up_read(&mm->mmap_sem);
> if (pages <= 0)
> return -EFAULT;
>
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index 8035cc1..dab8b19 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -76,16 +76,20 @@ static void async_pf_execute(struct work_struct *work)
> struct kvm_vcpu *vcpu = apf->vcpu;
> unsigned long addr = apf->addr;
> gva_t gva = apf->gva;
> + int locked = 1;
>
> might_sleep();
>
> /*
> * This work is run asynchromously to the task which owns
> * mm and might be done in another context, so we must
> - * use FOLL_REMOTE.
> + * access remotely.
> */
> - __get_user_pages_unlocked(NULL, mm, addr, 1, NULL,
> - FOLL_WRITE | FOLL_REMOTE);
> + down_read(&mm->mmap_sem);
> + get_user_pages_remote(NULL, mm, addr, 1, FOLL_WRITE, NULL, NULL,
> + &locked);
> + if (locked)
> + up_read(&mm->mmap_sem);
>
> kvm_async_page_present_sync(vcpu, apf);
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 2907b7b..c45d951 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1415,13 +1415,12 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
> npages = get_user_page_nowait(addr, write_fault, page);
> up_read(&current->mm->mmap_sem);
> } else {
> - unsigned int flags = FOLL_TOUCH | FOLL_HWPOISON;
> + unsigned int flags = FOLL_HWPOISON;
>
> if (write_fault)
> flags |= FOLL_WRITE;
>
> - npages = __get_user_pages_unlocked(current, current->mm, addr, 1,
> - page, flags);
> + npages = get_user_pages_unlocked(addr, 1, page, flags);
> }
> if (npages != 1)
> return npages;
> --
> 2.10.1

--
Michal Hocko
SUSE Labs