Re: [PATCH] vfio: pci: use kzalloc_flex

Alex Williamson
2026-03-30T22:19:38Z

[Cc +Leon]

On Wed, 25 Mar 2026 19:37:47 -0700
Rosen Penev <rosenp@gmail.com> wrote:

> Simplify allocation by using a flexible array member and kzalloc_flex.
> Less memory management needed.
>
> Use __counted_by for extra runtime analysis. Move assignment to after
> allocation as required by __counted_by.

I don't understand this statement, nr_ranges was previously set after
the allocation of phys_vec. The only reordering was relative to
setting vdev, but that appears arbitrary.

In fact, we don't need to explicitly set the __counted_by variable at
all, kzalloc_flex() handles that. So if anything, it's now redundant.

Leon, any other comments? This should have a v2 removing the
redundancy and fixing the commit log.

NB. This will be a bit messy to merge since kref and completion exist in
linux-next via drm, but maybe Linus will consolidate the hole in the
structure when he resolves it. Thanks,

Alex

>
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
> drivers/vfio/pci/vfio_pci_dmabuf.c | 18 +++++-------------
> 1 file changed, 5 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> index 3a803923141b..40e7e035a720 100644
> --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
> +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
> @@ -14,12 +14,12 @@ struct vfio_pci_dma_buf {
> struct vfio_pci_core_device *vdev;
> struct list_head dmabufs_elm;
> size_t size;
> - struct phys_vec *phys_vec;
> struct p2pdma_provider *provider;
> u32 nr_ranges;
> struct kref kref;
> struct completion comp;
> u8 revoked : 1;
> + struct phys_vec phys_vec[] __counted_by(nr_ranges);
> };
>
> static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
> @@ -95,7 +95,6 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
> up_write(&priv->vdev->memory_lock);
> vfio_device_put_registration(&priv->vdev->vdev);
> }
> - kfree(priv->phys_vec);
> kfree(priv);
> }
>
> @@ -258,33 +257,28 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
> if (ret)
> goto err_free_ranges;
>
> - priv = kzalloc_obj(*priv);
> + priv = kzalloc_flex(*priv, phys_vec, get_dma_buf.nr_ranges);
> if (!priv) {
> ret = -ENOMEM;
> goto err_free_ranges;
> }
> - priv->phys_vec = kzalloc_objs(*priv->phys_vec, get_dma_buf.nr_ranges);
> - if (!priv->phys_vec) {
> - ret = -ENOMEM;
> - goto err_free_priv;
> - }
>
> - priv->vdev = vdev;
> priv->nr_ranges = get_dma_buf.nr_ranges;
> + priv->vdev = vdev;
> priv->size = length;
> ret = vdev->pci_ops->get_dmabuf_phys(vdev, &priv->provider,
> get_dma_buf.region_index,
> priv->phys_vec, dma_ranges,
> priv->nr_ranges);
> if (ret)
> - goto err_free_phys;
> + goto err_free_priv;
>
> kfree(dma_ranges);
> dma_ranges = NULL;
>
> if (!vfio_device_try_get_registration(&vdev->vdev)) {
> ret = -ENODEV;
> - goto err_free_phys;
> + goto err_free_priv;
> }
>
> exp_info.ops = &vfio_pci_dmabuf_ops;
> @@ -323,8 +317,6 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
> dma_buf_put(priv->dmabuf);
> err_dev_put:
> vfio_device_put_registration(&vdev->vdev);
> -err_free_phys:
> - kfree(priv->phys_vec);
> err_free_priv:
> kfree(priv);