linux-kernel - [RFC PATCH] xen/gntdev.c: Convert get_user_pages*() to pin_user

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Date:   Tue, 18 Aug 2020 10:02:20 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     boris.ostrovsky@...cle.com, jgross@...e.com, sstabellini@...nel.org
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Souptick Joarder <jrdr.linux@...il.com>,
        John Hubbard <jhubbard@...dia.com>
Subject: [RFC PATCH] xen/gntdev.c: Convert get_user_pages*() to pin_user_pages*()

In 2019, we introduced pin_user_pages*() and now we are converting
get_user_pages*() to the new API as appropriate. [1] & [2] could
be referred for more information. This is case 5 as per document [1].

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
        https://lwn.net/Articles/807108/

Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
Cc: John Hubbard <jhubbard@...dia.com>
---
 drivers/xen/gntdev.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 64a9025a..e480509 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -730,7 +730,7 @@ static int gntdev_get_page(struct gntdev_copy_batch *batch, void __user *virt,
 	unsigned long xen_pfn;
 	int ret;
 
-	ret = get_user_pages_fast(addr, 1, writeable ? FOLL_WRITE : 0, &page);
+	ret = pin_user_pages_fast(addr, 1, writeable ? FOLL_WRITE : 0, &page);
 	if (ret < 0)
 		return ret;
 
@@ -744,10 +744,7 @@ static int gntdev_get_page(struct gntdev_copy_batch *batch, void __user *virt,
 
 static void gntdev_put_pages(struct gntdev_copy_batch *batch)
 {
-	unsigned int i;
-
-	for (i = 0; i < batch->nr_pages; i++)
-		put_page(batch->pages[i]);
+	unpin_user_pages(batch->pages, batch->nr_pages);
 	batch->nr_pages = 0;
 }
 
-- 
1.9.1