On Mon, Mar 30, 2026 at 06:23:05PM -0600, Alex Williamson wrote: > On Mon, Mar 30, 2026, at 5:24 PM, Rosen Penev wrote: > > On Mon, Mar 30, 2026 at 4:16 PM Alex Williamson <[email protected]> wrote: > >> > >> [Cc +Leon] > >> > >> On Wed, 25 Mar 2026 19:37:47 -0700 > >> Rosen Penev <[email protected]> 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. > > Sorry, this seems like a -2 on Rusty's manifesto of API design[1]. Why are > we doing this? We could do the math to do a single allocation and add the > annotation for UBSAN without introducing this helper that's not obvious how > to use correctly and at best introduces a redundant counter initialization. > Thanks,
My comment is that we can simply drop this patch. It adds no value and only creates unnecessary churn. Thanks > > Alex > > [1] https://gist.github.com/mjball/9cd028ac793ae8b351df1379f1e721f9 > > >> > >> 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 <[email protected]> > >> > --- > >> > 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: > >>
