netdev - [PATCH v2 20/34] xen: convert put_page() to put_user

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Date:   Sun,  4 Aug 2019 15:49:01 -0700
From:   john.hubbard@...il.com
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jérôme Glisse <jglisse@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx@...ts.freedesktop.org, ceph-devel@...r.kernel.org,
        devel@...verdev.osuosl.org, devel@...ts.orangefs.org,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-fbdev@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-mm@...ck.org,
        linux-nfs@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org, linux-xfs@...r.kernel.org,
        netdev@...r.kernel.org, rds-devel@....oracle.com,
        sparclinux@...r.kernel.org, x86@...nel.org,
        xen-devel@...ts.xenproject.org, John Hubbard <jhubbard@...dia.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: [PATCH v2 20/34] xen: convert put_page() to put_user_page*()

From: John Hubbard <jhubbard@...dia.com>

For pages that were retained via get_user_pages*(), release those pages
via the new put_user_page*() routines, instead of via put_page() or
release_pages().

This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
("mm: introduce put_user_page*(), placeholder versions").

This also handles pages[i] == NULL cases, thanks to an approach
that is actually written by Juergen Gross.

Signed-off-by: Juergen Gross <jgross@...e.com>
Signed-off-by: John Hubbard <jhubbard@...dia.com>

Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: xen-devel@...ts.xenproject.org
---

Hi Juergen,

Say, this is *exactly* what you proposed in your gup.patch, so
I've speculatively added your Signed-off-by above, but need your
approval before that's final. Let me know please...

thanks,
John Hubbard


 drivers/xen/privcmd.c | 32 +++++++++++---------------------
 1 file changed, 11 insertions(+), 21 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index c6070e70dd73..c7d0763ca8c2 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -582,10 +582,11 @@ static long privcmd_ioctl_mmap_batch(
 
 static int lock_pages(
 	struct privcmd_dm_op_buf kbufs[], unsigned int num,
-	struct page *pages[], unsigned int nr_pages)
+	struct page *pages[], unsigned int *nr_pages)
 {
-	unsigned int i;
+	unsigned int i, free = *nr_pages;
 
+	*nr_pages = 0;
 	for (i = 0; i < num; i++) {
 		unsigned int requested;
 		int pinned;
@@ -593,35 +594,22 @@ static int lock_pages(
 		requested = DIV_ROUND_UP(
 			offset_in_page(kbufs[i].uptr) + kbufs[i].size,
 			PAGE_SIZE);
-		if (requested > nr_pages)
+		if (requested > free)
 			return -ENOSPC;
 
 		pinned = get_user_pages_fast(
 			(unsigned long) kbufs[i].uptr,
-			requested, FOLL_WRITE, pages);
+			requested, FOLL_WRITE, pages + *nr_pages);
 		if (pinned < 0)
 			return pinned;
 
-		nr_pages -= pinned;
-		pages += pinned;
+		free -= pinned;
+		*nr_pages += pinned;
 	}
 
 	return 0;
 }
 
-static void unlock_pages(struct page *pages[], unsigned int nr_pages)
-{
-	unsigned int i;
-
-	if (!pages)
-		return;
-
-	for (i = 0; i < nr_pages; i++) {
-		if (pages[i])
-			put_page(pages[i]);
-	}
-}
-
 static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
 {
 	struct privcmd_data *data = file->private_data;
@@ -681,11 +669,12 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
 
 	xbufs = kcalloc(kdata.num, sizeof(*xbufs), GFP_KERNEL);
 	if (!xbufs) {
+		nr_pages = 0;
 		rc = -ENOMEM;
 		goto out;
 	}
 
-	rc = lock_pages(kbufs, kdata.num, pages, nr_pages);
+	rc = lock_pages(kbufs, kdata.num, pages, &nr_pages);
 	if (rc)
 		goto out;
 
@@ -699,7 +688,8 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
 	xen_preemptible_hcall_end();
 
 out:
-	unlock_pages(pages, nr_pages);
+	if (pages)
+		put_user_pages(pages, nr_pages);
 	kfree(xbufs);
 	kfree(pages);
 	kfree(kbufs);
-- 
2.22.0