[PATCH v5 27/28] virtio_balloon: disable reporting zeroed optimization for confidential guests

[Michael S. Tsirkin]

In confidential computing environments (TDX, SEV-SNP), the host
is untrusted and may lie about zeroing reported pages. Disable
host_zeroes_pages so the guest does not skip re-zeroing based on
the used_len hint from an untrusted device.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6
---
 drivers/virtio/virtio_balloon.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 708b0c344ae9..1eb9a6376038 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -18,6 +18,7 @@
 #include <linux/wait.h>
 #include <linux/mm.h>
 #include <linux/page_reporting.h>
+#include <linux/cc_platform.h>
 
 /*
  * Balloon device works in 4K page units.  So each page is pointed to by
@@ -1117,6 +1118,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
 #endif
 
 		vb->pr_dev_info.capacity = capacity;
+		vb->pr_dev_info.host_zeroes_pages =
+			!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT);
 		err = page_reporting_register(&vb->pr_dev_info);
 		if (err)
 			goto out_unregister_oom;
-- 
MST