On Tue, Nov 16, 2021 at 6:50 PM Christophe Leroy
<christophe.leroy@xxxxxxxxxx> wrote:
> fault_in_readable() and fault_in_writeable() perform __get_user()
> and __put_user() in a loop, implying multiple user access
> locking/unlocking.
>
> To avoid that, use user access blocks.
>
> Cc: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Reviewed-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
> ---
> mm/gup.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 2c51e9748a6a..be2a41feec7d 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1672,21 +1672,22 @@ size_t fault_in_writeable(char __user *uaddr, size_t size)
>
> if (unlikely(size == 0))
> return 0;
> + if (!user_write_access_begin(uaddr, size))
> + return size;
> if (!PAGE_ALIGNED(uaddr)) {
> - if (unlikely(__put_user(0, uaddr) != 0))
> - return size;
> + unsafe_put_user(0, uaddr, out);
> uaddr = (char __user *)PAGE_ALIGN((unsigned long)uaddr);
> }
> end = (char __user *)PAGE_ALIGN((unsigned long)start + size);
> if (unlikely(end < start))
> end = NULL;
> while (uaddr != end) {
> - if (unlikely(__put_user(0, uaddr) != 0))
> - goto out;
> + unsafe_put_user(0, uaddr, out);
> uaddr += PAGE_SIZE;
> }
>
> out:
> + user_write_access_end();
> if (size > uaddr - start)
> return size - (uaddr - start);
> return 0;
> @@ -1771,21 +1772,22 @@ size_t fault_in_readable(const char __user *uaddr, size_t size)
>
> if (unlikely(size == 0))
> return 0;
> + if (!user_read_access_begin(uaddr, size))
> + return size;
> if (!PAGE_ALIGNED(uaddr)) {
> - if (unlikely(__get_user(c, uaddr) != 0))
> - return size;
> + unsafe_get_user(c, uaddr, out);
> uaddr = (const char __user *)PAGE_ALIGN((unsigned long)uaddr);
> }
> end = (const char __user *)PAGE_ALIGN((unsigned long)start + size);
> if (unlikely(end < start))
> end = NULL;
> while (uaddr != end) {
> - if (unlikely(__get_user(c, uaddr) != 0))
> - goto out;
> + unsafe_get_user(c, uaddr, out);
> uaddr += PAGE_SIZE;
> }
>
> out:
> + user_read_access_end();
> (void)c;
> if (size > uaddr - start)
> return size - (uaddr - start);
> --
> 2.31.1
>
