linux-kernel - [PATCH 3/3] xen/gntdev: remove erronous use of copy_to

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Date:	Wed,  2 Jan 2013 17:57:13 -0500
From:	Daniel De Graaf <dgdegra@...ho.nsa.gov>
To:	viro@...IV.linux.org.uk, konrad.wilk@...cle.com
Cc:	david.vrabel@...rix.com, stefano.stabellini@...citrix.com,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	Daniel De Graaf <dgdegra@...ho.nsa.gov>
Subject: [PATCH 3/3] xen/gntdev: remove erronous use of copy_to_user

Since there is now a mapping of granted pages in kernel address space in
both PV and HVM, use it for UNMAP_NOTIFY_CLEAR_BYTE instead of accessing
memory via copy_to_user and triggering sleep-in-atomic warnings.

Signed-off-by: Daniel De Graaf <dgdegra@...ho.nsa.gov>
---
 drivers/xen/gntdev.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 9be3e5e..3c8803f 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -312,17 +312,10 @@ static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
 
 	if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
 		int pgno = (map->notify.addr >> PAGE_SHIFT);
-		if (pgno >= offset && pgno < offset + pages && use_ptemod) {
-			void __user *tmp = (void __user *)
-				map->vma->vm_start + map->notify.addr;
-			err = copy_to_user(tmp, &err, 1);
-			if (err)
-				return -EFAULT;
-			map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
-		} else if (pgno >= offset && pgno < offset + pages) {
-			uint8_t *tmp = kmap(map->pages[pgno]);
+		if (pgno >= offset && pgno < offset + pages) {
+			/* No need for kmap, pages are in lowmem */
+			uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno]));
 			tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
-			kunmap(map->pages[pgno]);
 			map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
 		}
 	}
-- 
1.7.11.7

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