Implement VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED (per virtio spec proposal): when negotiated, the device initializes reported pages (zeros, or poison_val if PAGE_POISON).
Check per-page used length returned by the device to determine which reported pages were zeroed. If used_len matches the page size, the device successfully initialized the page (e.g. via MADV_DONTNEED), and we set the corresponding zeroed_bitmap bit. Gate host_zeroes_pages on the feature bit and page content: when PAGE_POISON is negotiated with non-zero poison_val, the device fills with poison not zeros, so pages are not zeroed. Clear the feature in validate() if REPORTING is not present or if PAGE_POISON is active with non-zero poison_val. See the virtio spec change: https://github.com/oasis-tcs/virtio-spec/issues/244 Signed-off-by: Michael S. Tsirkin <[email protected]> Assisted-by: Claude:claude-opus-4-6 Assisted-by: cursor-agent:GPT-5.4-xhigh --- drivers/virtio/virtio_balloon.c | 22 ++++++++++++++++++++-- include/uapi/linux/virtio_balloon.h | 1 + 2 files changed, 21 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index fc43d0d7bbbc..6586699396b7 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -204,6 +204,8 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i struct virtqueue *vq = vb->reporting_vq; unsigned int i, err = 0; + bitmap_zero(pr_dev_info->zeroed_bitmap, nents); + /* We should always be able to add these buffers to an empty queue. */ for (i = 0; i < nents; i++) { struct scatterlist one; @@ -223,10 +225,14 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i /* When host has read buffer, this completes via balloon_ack */ for (i = 0; i < nents; i++) { - unsigned int unused; + struct scatterlist *entry; + unsigned int used_len; wait_event(vb->acked, - virtqueue_get_buf(vq, &unused)); + (entry = virtqueue_get_buf(vq, &used_len))); + if (used_len == entry->length) + set_bit(entry - sg, + pr_dev_info->zeroed_bitmap); } } @@ -1048,6 +1054,9 @@ static int virtballoon_probe(struct virtio_device *vdev) #endif vb->pr_dev_info.capacity = capacity; + vb->pr_dev_info.host_zeroes_pages = + virtio_has_feature(vdev, + VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED); err = page_reporting_register(&vb->pr_dev_info); if (err) goto out_unregister_oom; @@ -1173,6 +1182,14 @@ 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); + if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_REPORTING)) + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED); + + /* Device fills with poison_val, not zeros; disable zeroed hint */ + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON) && + !want_init_on_free()) + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED); + __virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM); return 0; } @@ -1184,6 +1201,7 @@ static unsigned int features[] = { VIRTIO_BALLOON_F_FREE_PAGE_HINT, VIRTIO_BALLOON_F_PAGE_POISON, VIRTIO_BALLOON_F_REPORTING, + VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED, }; static struct virtio_driver virtio_balloon_driver = { diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h index ee35a372805d..13074631f300 100644 --- a/include/uapi/linux/virtio_balloon.h +++ b/include/uapi/linux/virtio_balloon.h @@ -37,6 +37,7 @@ #define VIRTIO_BALLOON_F_FREE_PAGE_HINT 3 /* VQ to report free pages */ #define VIRTIO_BALLOON_F_PAGE_POISON 4 /* Guest is using page poisoning */ #define VIRTIO_BALLOON_F_REPORTING 5 /* Page reporting virtqueue */ +#define VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED 6 /* Device initializes reported pages */ /* Size of a PFN in the balloon interface. */ #define VIRTIO_BALLOON_PFN_SHIFT 12 -- MST
