Re: [PATCH] vfio: pci: use kzalloc_flex

Rosen Penev
2026-03-30T23:24:33Z

On Mon, Mar 30, 2026 at 4:16 PM Alex Williamson <alex@shazbot.org> wrote:
>
> [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.
Yes that one. My understanding is __counted_by mandates immediate
assignment after allocation. Otherwise UBSAN complains.
>
> 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.
Redundant with GCC`15 and above.
>
> 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);
> > err_free_ranges:
>