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From:   David Howells <dhowells@redhat.com>
To:     Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>
Cc:     David Howells <dhowells@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        Logan Gunthorpe <logang@deltatee.com>,
        linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v7 1/8] iov_iter: Define flags to qualify page extraction.
Date:   Fri, 20 Jan 2023 17:55:49 +0000
Message-Id: <20230120175556.3556978-2-dhowells@redhat.com>
In-Reply-To: <20230120175556.3556978-1-dhowells@redhat.com>
References: <20230120175556.3556978-1-dhowells@redhat.com>
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Define flags to qualify page extraction to pass into iov_iter_*_pages*()
rather than passing in FOLL_* flags.

For now only a flag to allow peer-to-peer DMA is allowed; but in future,
additional flags will be provided to indicate the I/O direction.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Christoph Hellwig <hch@infradead.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Logan Gunthorpe <logang@deltatee.com>
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
---

Notes:
    ver #7)
     - Don't use FOLL_* as a parameter, but rather define constants
       specifically to use with iov_iter_*_pages*().
     - Drop the I/O direction constants for now.

 block/bio.c         |  6 +++---
 block/blk-map.c     |  8 ++++----
 include/linux/uio.h |  7 +++++--
 lib/iov_iter.c      | 14 ++++++++------
 4 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 5f96fcae3f75..6a6c73d14bfd 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1249,7 +1249,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
 	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
 	struct page **pages = (struct page **)bv;
-	unsigned int gup_flags = 0;
+	unsigned int extract_flags = 0;
 	ssize_t size, left;
 	unsigned len, i = 0;
 	size_t offset, trim;
@@ -1264,7 +1264,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
 
 	if (bio->bi_bdev && blk_queue_pci_p2pdma(bio->bi_bdev->bd_disk->queue))
-		gup_flags |= FOLL_PCI_P2PDMA;
+		extract_flags |= ITER_ALLOW_P2PDMA;
 
 	/*
 	 * Each segment in the iov is required to be a block size multiple.
@@ -1275,7 +1275,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	 */
 	size = iov_iter_get_pages(iter, pages,
 				  UINT_MAX - bio->bi_iter.bi_size,
-				  nr_pages, &offset, gup_flags);
+				  nr_pages, &offset, extract_flags);
 	if (unlikely(size <= 0))
 		return size ? size : -EFAULT;
 
diff --git a/block/blk-map.c b/block/blk-map.c
index 19940c978c73..bc111261fc82 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -267,7 +267,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 {
 	unsigned int max_sectors = queue_max_hw_sectors(rq->q);
 	unsigned int nr_vecs = iov_iter_npages(iter, BIO_MAX_VECS);
-	unsigned int gup_flags = 0;
+	unsigned int extract_flags = 0;
 	struct bio *bio;
 	int ret;
 	int j;
@@ -280,7 +280,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 		return -ENOMEM;
 
 	if (blk_queue_pci_p2pdma(rq->q))
-		gup_flags |= FOLL_PCI_P2PDMA;
+		extract_flags |= ITER_ALLOW_P2PDMA;
 
 	while (iov_iter_count(iter)) {
 		struct page **pages, *stack_pages[UIO_FASTIOV];
@@ -291,10 +291,10 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 		if (nr_vecs <= ARRAY_SIZE(stack_pages)) {
 			pages = stack_pages;
 			bytes = iov_iter_get_pages(iter, pages, LONG_MAX,
-						   nr_vecs, &offs, gup_flags);
+						   nr_vecs, &offs, extract_flags);
 		} else {
 			bytes = iov_iter_get_pages_alloc(iter, &pages,
-						LONG_MAX, &offs, gup_flags);
+						LONG_MAX, &offs, extract_flags);
 		}
 		if (unlikely(bytes <= 0)) {
 			ret = bytes ? bytes : -EFAULT;
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 9f158238edba..46d5080314c6 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -252,12 +252,12 @@ void iov_iter_xarray(struct iov_iter *i, unsigned int direction, struct xarray *
 		     loff_t start, size_t count);
 ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages,
 		size_t maxsize, unsigned maxpages, size_t *start,
-		unsigned gup_flags);
+		unsigned extract_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(struct iov_iter *i,
 		struct page ***pages, size_t maxsize, size_t *start,
-		unsigned gup_flags);
+		unsigned extract_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);
@@ -360,4 +360,7 @@ static inline void iov_iter_ubuf(struct iov_iter *i, unsigned int direction,
 	};
 }
 
+/* Flags for iov_iter_get/extract_pages*() */
+#define ITER_ALLOW_P2PDMA	0x01	/* Allow P2PDMA on the extracted pages */
+
 #endif
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index f9a3ff37ecd1..fb04abe7d746 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1432,9 +1432,9 @@ 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 gup_flags)
+		   unsigned int extract_flags)
 {
-	unsigned int n;
+	unsigned int n, gup_flags = 0;
 
 	if (maxsize > i->count)
 		maxsize = i->count;
@@ -1442,6 +1442,8 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
 		return 0;
 	if (maxsize > MAX_RW_COUNT)
 		maxsize = MAX_RW_COUNT;
+	if (extract_flags & ITER_ALLOW_P2PDMA)
+		gup_flags |= FOLL_PCI_P2PDMA;
 
 	if (likely(user_backed_iter(i))) {
 		unsigned long addr;
@@ -1495,14 +1497,14 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
 
 ssize_t iov_iter_get_pages(struct iov_iter *i,
 		   struct page **pages, size_t maxsize, unsigned maxpages,
-		   size_t *start, unsigned gup_flags)
+		   size_t *start, unsigned extract_flags)
 {
 	if (!maxpages)
 		return 0;
 	BUG_ON(!pages);
 
 	return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages,
-					  start, gup_flags);
+					  start, extract_flags);
 }
 EXPORT_SYMBOL_GPL(iov_iter_get_pages);
 
@@ -1515,14 +1517,14 @@ EXPORT_SYMBOL(iov_iter_get_pages2);
 
 ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
 		   struct page ***pages, size_t maxsize,
-		   size_t *start, unsigned gup_flags)
+		   size_t *start, unsigned extract_flags)
 {
 	ssize_t len;
 
 	*pages = NULL;
 
 	len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start,
-					 gup_flags);
+					 extract_flags);
 	if (len <= 0) {
 		kvfree(*pages);
 		*pages = NULL;