FAILED: patch "[PATCH] xen/gntdev.c: Mark pages as dirty" failed to apply to 4.9-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 779055842da5b2e508f3ccf9a8153cb1f704f566 Mon Sep 17 00:00:00 2001
From: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Date: Sun, 6 Sep 2020 12:21:53 +0530
Subject: [PATCH] xen/gntdev.c: Mark pages as dirty

There seems to be a bug in the original code when gntdev_get_page()
is called with writeable=true then the page needs to be marked dirty
before being put.

To address this, a bool writeable is added in gnt_dev_copy_batch, set
it in gntdev_grant_copy_seg() (and drop `writeable` argument to
gntdev_get_page()) and then, based on batch->writeable, use
set_page_dirty_lock().

Fixes: a4cdb556cae0 (xen/gntdev: add ioctl for grant copy)
Suggested-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/1599375114-32360-1-git-send-email-jrdr.linux@xxxxxxxxx
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 64a9025a87be..1f32db7b72b2 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -720,17 +720,18 @@ struct gntdev_copy_batch {
 	s16 __user *status[GNTDEV_COPY_BATCH];
 	unsigned int nr_ops;
 	unsigned int nr_pages;
+	bool writeable;
 };
 
 static int gntdev_get_page(struct gntdev_copy_batch *batch, void __user *virt,
-			   bool writeable, unsigned long *gfn)
+				unsigned long *gfn)
 {
 	unsigned long addr = (unsigned long)virt;
 	struct page *page;
 	unsigned long xen_pfn;
 	int ret;
 
-	ret = get_user_pages_fast(addr, 1, writeable ? FOLL_WRITE : 0, &page);
+	ret = get_user_pages_fast(addr, 1, batch->writeable ? FOLL_WRITE : 0, &page);
 	if (ret < 0)
 		return ret;
 
@@ -746,9 +747,13 @@ static void gntdev_put_pages(struct gntdev_copy_batch *batch)
 {
 	unsigned int i;
 
-	for (i = 0; i < batch->nr_pages; i++)
+	for (i = 0; i < batch->nr_pages; i++) {
+		if (batch->writeable && !PageDirty(batch->pages[i]))
+			set_page_dirty_lock(batch->pages[i]);
 		put_page(batch->pages[i]);
+	}
 	batch->nr_pages = 0;
+	batch->writeable = false;
 }
 
 static int gntdev_copy(struct gntdev_copy_batch *batch)
@@ -837,8 +842,9 @@ static int gntdev_grant_copy_seg(struct gntdev_copy_batch *batch,
 			virt = seg->source.virt + copied;
 			off = (unsigned long)virt & ~XEN_PAGE_MASK;
 			len = min(len, (size_t)XEN_PAGE_SIZE - off);
+			batch->writeable = false;
 
-			ret = gntdev_get_page(batch, virt, false, &gfn);
+			ret = gntdev_get_page(batch, virt, &gfn);
 			if (ret < 0)
 				return ret;
 
@@ -856,8 +862,9 @@ static int gntdev_grant_copy_seg(struct gntdev_copy_batch *batch,
 			virt = seg->dest.virt + copied;
 			off = (unsigned long)virt & ~XEN_PAGE_MASK;
 			len = min(len, (size_t)XEN_PAGE_SIZE - off);
+			batch->writeable = true;
 
-			ret = gntdev_get_page(batch, virt, true, &gfn);
+			ret = gntdev_get_page(batch, virt, &gfn);
 			if (ret < 0)
 				return ret;