Re: [PATCH v9 2/8] iov_iter: introduce iov_iter_get_pages_[alloc_]flags()

John Hubbard
2022-09-05T23:21:28Z

On 8/25/22 08:24, Logan Gunthorpe wrote:
> Add iov_iter_get_pages_flags() and iov_iter_get_pages_alloc_flags()
> which take a flags argument that is passed to get_user_pages_fast().
>
> This is so that FOLL_PCI_P2PDMA can be passed when appropriate.
>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> ---
> include/linux/uio.h | 6 ++++++
> lib/iov_iter.c | 40 ++++++++++++++++++++++++++++++++++++----
> 2 files changed, 42 insertions(+), 4 deletions(-)
>

Yes.

I also don't object to Christoph's additional request to refactor and
rename around iov_iter_get_pages2() and such, but this version here is
perfectly good, so please feel free to add:

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

Looking ahead, interestingly enough, it turns out that this approach to
the wrappers is really pretty close to what I posted in patch 4/7 of my
"convert most filesystems to pin_user_pages_fast()" series [1]. Instead
of passing gup_flags through, I tried to avoid that (because FOLL_PIN
is, as a mild design preference, supposed to remain internal to gup.c),
but given that you need to do it, I think I can just build on top of
your approach, and pass in FOLL_PIN via your new gup_flags arg.

Along those lines, I've copied you in on "New topic branch for block +
gup work?", let's see what happens over there.

[1] https://lore.kernel.org/r/20220831041843.973026-1-jhubbard@nvidia.com

thanks,

--
John Hubbard
NVIDIA
> diff --git a/include/linux/uio.h b/include/linux/uio.h
> index 5896af36199c..76ba69edb8c5 100644
> --- a/include/linux/uio.h
> +++ b/include/linux/uio.h
> @@ -247,8 +247,14 @@ void iov_iter_pipe(struct iov_iter *i, unsigned int direction, struct pipe_inode
> void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count);
> void iov_iter_xarray(struct iov_iter *i, unsigned int direction, struct xarray *xarray,
> loff_t start, size_t count);
> +ssize_t iov_iter_get_pages_flags(struct iov_iter *i, struct page **pages,
> + size_t maxsize, unsigned maxpages, size_t *start,
> + unsigned int gup_flags);
> ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages,
> size_t maxsize, unsigned maxpages, size_t *start);
> +ssize_t iov_iter_get_pages_alloc_flags(struct iov_iter *i,
> + struct page ***pages, size_t maxsize, size_t *start,
> + unsigned int gup_flags);
> ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i, struct page ***pages,
> size_t maxsize, size_t *start);
> int iov_iter_npages(const struct iov_iter *i, int maxpages);
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 4b7fce72e3e5..dedb78f3c655 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1427,7 +1427,8 @@ static struct page *first_bvec_segment(const struct iov_iter *i,
>
> static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
> struct page ***pages, size_t maxsize,
> - unsigned int maxpages, size_t *start)
> + unsigned int maxpages, size_t *start,
> + unsigned int gup_flags)
> {
> unsigned int n;
>
> @@ -1439,7 +1440,6 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
> maxsize = MAX_RW_COUNT;
>
> if (likely(user_backed_iter(i))) {
> - unsigned int gup_flags = 0;
> unsigned long addr;
> int res;
>
> @@ -1497,10 +1497,24 @@ ssize_t iov_iter_get_pages2(struct iov_iter *i,
> return 0;
> BUG_ON(!pages);
>
> - return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages, start);
> + return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages,
> + start, 0);
> }
> EXPORT_SYMBOL(iov_iter_get_pages2);
>
> +ssize_t iov_iter_get_pages_flags(struct iov_iter *i, struct page **pages,
> + size_t maxsize, unsigned maxpages, size_t *start,
> + unsigned int gup_flags)
> +{
> + if (!maxpages)
> + return 0;
> + BUG_ON(!pages);
> +
> + return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages,
> + start, gup_flags);
> +}
> +EXPORT_SYMBOL_GPL(iov_iter_get_pages_flags);
> +
> ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i,
> struct page ***pages, size_t maxsize,
> size_t *start)
> @@ -1509,7 +1523,7 @@ ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i,
>
> *pages = NULL;
>
> - len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start);
> + len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start, 0);
> if (len <= 0) {
> kvfree(*pages);
> *pages = NULL;
> @@ -1518,6 +1532,24 @@ ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i,
> }
> EXPORT_SYMBOL(iov_iter_get_pages_alloc2);
>
> +ssize_t iov_iter_get_pages_alloc_flags(struct iov_iter *i,
> + struct page ***pages, size_t maxsize,
> + size_t *start, unsigned int gup_flags)
> +{
> + ssize_t len;
> +
> + *pages = NULL;
> +
> + len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start,
> + gup_flags);
> + if (len <= 0) {
> + kvfree(*pages);
> + *pages = NULL;
> + }
> + return len;
> +}
> +EXPORT_SYMBOL_GPL(iov_iter_get_pages_alloc_flags);
> +
> size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
> struct iov_iter *i)
> {