Patchwork [116/222] virtio: force vring descriptors to be allocated from lowmem

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Submitter Herton Ronaldo Krzesinski
Date Jan. 16, 2013, 3:55 p.m.
Message ID <>
Download mbox | patch
Permalink /patch/212693/
State New
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Herton Ronaldo Krzesinski - Jan. 16, 2013, 3:55 p.m. -stable review patch.  If anyone has any objections, please let me know.


From: Will Deacon <>

commit b92b1b89a33c172c075edccf6afb0edc41d851fd upstream.

Virtio devices may attempt to add descriptors to a virtqueue from atomic
context using GFP_ATOMIC allocation. This is problematic because such
allocations can fall outside of the lowmem mapping, causing virt_to_phys
to report bogus physical addresses which are subsequently passed to
userspace via the buffers for the virtual device.

This patch masks out __GFP_HIGH and __GFP_HIGHMEM from the requested
flags when allocating descriptors for a virtqueue. If an atomic
allocation is requested and later fails, we will return -ENOSPC which
will be handled by the driver.

Cc: Sasha Levin <>
Signed-off-by: Will Deacon <>
Signed-off-by: Rusty Russell <>
Signed-off-by: Herton Ronaldo Krzesinski <>
 drivers/virtio/virtio_ring.c |    7 +++++++
 1 file changed, 7 insertions(+)


diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 5aa43c3..52bfd07 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -132,6 +132,13 @@  static int vring_add_indirect(struct vring_virtqueue *vq,
 	unsigned head;
 	int i;
+	/*
+	 * We require lowmem mappings for the descriptors because
+	 * otherwise virt_to_phys will give us bogus addresses in the
+	 * virtqueue.
+	 */
+	gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);
 	desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
 	if (!desc)
 		return -ENOMEM;