* [PATCH splitout] virtio_balloon: disable indirect descriptors
@ 2026-06-09 16:33 Michael S. Tsirkin
2026-06-15 16:11 ` David Hildenbrand (Arm)
0 siblings, 1 reply; 2+ messages in thread
From: Michael S. Tsirkin @ 2026-06-09 16:33 UTC (permalink / raw)
To: linux-kernel
Cc: Miaohe Lin, David Hildenbrand (Arm), Jason Wang, Xuan Zhuo,
Eugenio Pérez, Muchun Song, Oscar Salvador, Andrew Morton,
Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli, Naoya Horiguchi,
Alexander Duyck
The page reporting callback submits an sg list to the reporting
virtqueue. With VIRTIO_RING_F_INDIRECT_DESC negotiated and
total_sg > 1 (which it typically is), virtqueue_add reports it to the
host by allocating an indirect descriptor via kmalloc(GFP_KERNEL).
This is not pretty: the reporting worker isolates potentially hundreds
of MB of free pages from the buddy allocator (reported pages are at
least pageblock_order, and the sg can contain up to
PAGE_REPORTING_CAPACITY entries of varying orders). As the result, at
least in theory, the kmalloc might trigger OOM when we have in fact a
ton of free memory.
Clear VIRTIO_RING_F_INDIRECT_DESC, to avoid using indirect descriptors.
Fixes: b0c504f15471 ("virtio-balloon: add support for providing free page reports to host")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
drivers/virtio/virtio_balloon.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 53b4a3984e7d..6698edb61474 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -7,6 +7,7 @@
*/
#include <linux/virtio.h>
+#include <uapi/linux/virtio_ring.h>
#include <linux/virtio_balloon.h>
#include <linux/swap.h>
#include <linux/workqueue.h>
@@ -1175,6 +1176,11 @@ static int virtballoon_validate(struct virtio_device *vdev)
else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))
__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
+ /*
+ * Disable indirect descriptors to avoid memory allocation in
+ * virtqueue_add during page reporting.
+ */
+ __virtio_clear_bit(vdev, VIRTIO_RING_F_INDIRECT_DESC);
__virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
return 0;
}
--
MST
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH splitout] virtio_balloon: disable indirect descriptors
2026-06-09 16:33 [PATCH splitout] virtio_balloon: disable indirect descriptors Michael S. Tsirkin
@ 2026-06-15 16:11 ` David Hildenbrand (Arm)
0 siblings, 0 replies; 2+ messages in thread
From: David Hildenbrand (Arm) @ 2026-06-15 16:11 UTC (permalink / raw)
To: Michael S. Tsirkin, linux-kernel
Cc: Miaohe Lin, Jason Wang, Xuan Zhuo, Eugenio Pérez,
Muchun Song, Oscar Salvador, Andrew Morton, Lorenzo Stoakes,
Liam R. Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Brendan Jackman,
Johannes Weiner, Zi Yan, Baolin Wang, Nico Pache, Ryan Roberts,
Dev Jain, Barry Song, Lance Yang, Hugh Dickins, Matthew Brost,
Joshua Hahn, Rakie Kim, Byungchul Park, Gregory Price, Ying Huang,
Alistair Popple, Christoph Lameter, David Rientjes,
Roman Gushchin, Harry Yoo, Axel Rasmussen, Yuanchu Xie, Wei Xu,
Chris Li, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
virtualization, linux-mm, Andrea Arcangeli, Naoya Horiguchi,
Alexander Duyck
On 6/9/26 18:33, Michael S. Tsirkin wrote:
> The page reporting callback submits an sg list to the reporting
> virtqueue. With VIRTIO_RING_F_INDIRECT_DESC negotiated and
> total_sg > 1 (which it typically is), virtqueue_add reports it to the
> host by allocating an indirect descriptor via kmalloc(GFP_KERNEL).
>
> This is not pretty: the reporting worker isolates potentially hundreds
> of MB of free pages from the buddy allocator (reported pages are at
> least pageblock_order, and the sg can contain up to
> PAGE_REPORTING_CAPACITY entries of varying orders). As the result, at
> least in theory, the kmalloc might trigger OOM when we have in fact a
> ton of free memory.
Very theoretical, given that we isolate large pageblocks and the kmalloc would
just need likely a single page. But yeah, avodiing to allocate memory where
possible on these paths makes sense I guess.
>
> Clear VIRTIO_RING_F_INDIRECT_DESC, to avoid using indirect descriptors.
>
> Fixes: b0c504f15471 ("virtio-balloon: add support for providing free page reports to host")
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Assisted-by: Claude:claude-opus-4-6
> ---
> drivers/virtio/virtio_balloon.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 53b4a3984e7d..6698edb61474 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -7,6 +7,7 @@
> */
>
> #include <linux/virtio.h>
> +#include <uapi/linux/virtio_ring.h>
> #include <linux/virtio_balloon.h>
> #include <linux/swap.h>
> #include <linux/workqueue.h>
> @@ -1175,6 +1176,11 @@ static int virtballoon_validate(struct virtio_device *vdev)
> else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))
> __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
>
> + /*
> + * Disable indirect descriptors to avoid memory allocation in
> + * virtqueue_add during page reporting.
> + */
> + __virtio_clear_bit(vdev, VIRTIO_RING_F_INDIRECT_DESC);
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
--
Cheers,
David
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