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

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Date:   Wed, 17 Jun 2020 08:44:58 +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/privcmd: 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.

[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>
---
Hi,

I have compile tested this patch but unable to run-time test,
so any testing help is much appriciated.

Also have a question, why the existing code is not marking the
pages dirty (since it did FOLL_WRITE) ?

 drivers/xen/privcmd.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index a250d11..543739e 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -594,7 +594,7 @@ static int lock_pages(
 		if (requested > nr_pages)
 			return -ENOSPC;
 
-		pinned = get_user_pages_fast(
+		pinned = pin_user_pages_fast(
 			(unsigned long) kbufs[i].uptr,
 			requested, FOLL_WRITE, pages);
 		if (pinned < 0)
@@ -614,10 +614,7 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
 	if (!pages)
 		return;
 
-	for (i = 0; i < nr_pages; i++) {
-		if (pages[i])
-			put_page(pages[i]);
-	}
+	unpin_user_pages(pages, nr_pages);
 }
 
 static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
-- 
1.9.1