When the device offers DEVICE_INIT_ON_INFLATE (bit 7), the device initializes inflated pages and returns a per-page bitmap indicating which pages were successfully initialized.
The driver appends a device-writable bitmap buffer to each inflate descriptor chain via virtqueue_add_sgs. After the host acknowledges, the driver checks bitmap bits (bounded by used_len) and marks pages with SetPageZeroed. tell_host() returns used_len from virtqueue_get_buf(). Bitmap reads are bounded: fill_balloon() and virtballoon_migratepage() only trust bits within the used_len range. On deflate, release_pages_balloon checks PageZeroed per page and uses put_page_zeroed for pages the host initialized, propagating the zeroed hint to the buddy allocator. If inflate_vq has fewer than 2 descriptors, the feature is cleared at probe time. If PAGE_POISON is negotiated with non-zero poison_val, the feature is cleared in validate(). See the virtio spec change: https://lore.kernel.org/all/9c69b992c3dd83dfef3db92cd86b2fd8a0730d48.1777731396.git....@redhat.com 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 | 97 +++++++++++++++++++++++++---- include/uapi/linux/virtio_balloon.h | 1 + 2 files changed, 87 insertions(+), 11 deletions(-) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index e99ffbbdd2bd..708b0c344ae9 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -120,6 +120,9 @@ struct virtio_balloon { struct virtqueue *reporting_vq; struct page_reporting_dev_info pr_dev_info; + /* Bitmap returned by host for DEVICE_INIT_ON_INFLATE */ + DECLARE_BITMAP(inflate_bitmap, VIRTIO_BALLOON_ARRAY_PFNS_MAX); + /* State for keeping the wakeup_source active while adjusting the balloon */ spinlock_t wakeup_lock; bool processing_wakeup_event; @@ -180,20 +183,30 @@ static void balloon_ack(struct virtqueue *vq) wake_up(&vb->acked); } -static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq) +static unsigned int tell_host(struct virtio_balloon *vb, struct virtqueue *vq) { - struct scatterlist sg; + struct scatterlist sg_out, sg_in; + struct scatterlist *sgs[] = { &sg_out, &sg_in }; unsigned int len; - sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns); + sg_init_one(&sg_out, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns); - /* We should always be able to add one buffer to an empty queue. */ - virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); + if (vq == vb->inflate_vq && + virtio_has_feature(vb->vdev, + VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE)) { + unsigned int bitmap_bytes; + + bitmap_bytes = DIV_ROUND_UP(vb->num_pfns, 8); + bitmap_zero(vb->inflate_bitmap, vb->num_pfns); + sg_init_one(&sg_in, vb->inflate_bitmap, bitmap_bytes); + virtqueue_add_sgs(vq, sgs, 1, 1, vb, GFP_KERNEL); + } else { + virtqueue_add_outbuf(vq, &sg_out, 1, vb, GFP_KERNEL); + } virtqueue_kick(vq); - /* When host has read buffer, this completes via balloon_ack */ wait_event(vb->acked, virtqueue_get_buf(vq, &len)); - + return len; } static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info, @@ -290,8 +303,37 @@ static unsigned int fill_balloon(struct virtio_balloon *vb, size_t num) num_allocated_pages = vb->num_pfns; /* Did we get any? */ - if (vb->num_pfns != 0) - tell_host(vb, vb->inflate_vq); + if (vb->num_pfns != 0) { + unsigned int used_len = tell_host(vb, vb->inflate_vq); + + if (virtio_has_feature(vb->vdev, + VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE)) { + unsigned int i; + unsigned int valid_bits = used_len * 8; + + for (i = 0; i < vb->num_pfns; + i += VIRTIO_BALLOON_PAGES_PER_PAGE) { + unsigned int pfn, j; + bool zeroed = true; + + if (i + VIRTIO_BALLOON_PAGES_PER_PAGE > valid_bits) + break; + for (j = 0; j < VIRTIO_BALLOON_PAGES_PER_PAGE; j++) { + if (!test_bit(i + j, vb->inflate_bitmap)) { + zeroed = false; + break; + } + } + if (zeroed) { + pfn = virtio32_to_cpu(vb->vdev, + vb->pfns[i]); + __SetPageZeroed(pfn_to_page(pfn >> + (PAGE_SHIFT - + VIRTIO_BALLOON_PFN_SHIFT))); + } + } + } + } mutex_unlock(&vb->balloon_lock); return num_allocated_pages; @@ -304,7 +346,12 @@ static void release_pages_balloon(struct virtio_balloon *vb, list_for_each_entry_safe(page, next, pages, lru) { list_del(&page->lru); - put_page(page); /* balloon reference */ + if (PageZeroed(page)) { + __ClearPageZeroed(page); + put_page_zeroed(page); + } else { + put_page(page); + } } } @@ -851,7 +898,25 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info, /* balloon's page migration 1st step -- inflate "newpage" */ vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; set_page_pfns(vb, vb->pfns, newpage); - tell_host(vb, vb->inflate_vq); + { + unsigned int used_len = tell_host(vb, vb->inflate_vq); + + if (virtio_has_feature(vb->vdev, + VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE) && + used_len >= DIV_ROUND_UP(VIRTIO_BALLOON_PAGES_PER_PAGE, 8)) { + unsigned int j; + bool zeroed = true; + + for (j = 0; j < VIRTIO_BALLOON_PAGES_PER_PAGE; j++) { + if (!test_bit(j, vb->inflate_bitmap)) { + zeroed = false; + break; + } + } + if (zeroed) + __SetPageZeroed(newpage); + } + } /* balloon's page migration 2nd step -- deflate "page" */ vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; @@ -956,6 +1021,12 @@ static int virtballoon_probe(struct virtio_device *vdev) if (err) goto out_free_vb; + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE) && + virtqueue_get_vring_size(vb->inflate_vq) < 2) { + err = -ENOSPC; + goto out_del_vqs; + } + if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) vb->vb_dev_info.adjust_managed_page_count = true; #ifdef CONFIG_BALLOON_MIGRATION @@ -1171,6 +1242,9 @@ 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_PAGE_POISON) && + !want_init_on_free()) + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE); __virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM); return 0; } @@ -1182,6 +1256,7 @@ static unsigned int features[] = { VIRTIO_BALLOON_F_FREE_PAGE_HINT, VIRTIO_BALLOON_F_PAGE_POISON, VIRTIO_BALLOON_F_REPORTING, + VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE, }; 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..d129736cc3a8 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_ON_INFLATE 6 /* Device initializes pages on inflate */ /* Size of a PFN in the balloon interface. */ #define VIRTIO_BALLOON_PFN_SHIFT 12 -- MST
