drivers/vfio/pci/vfio_pci_dmabuf.c | 18 +++++------------- 1 file changed, 5 insertions(+), 13 deletions(-)
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.
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:
--
2.53.0[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);
> err_free_ranges:
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:
>
On 3/30/26 17:24, Rosen Penev wrote: > 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. Not true. However, it's best practice. The requirement is that the _counter_ must be initialized before the first reference to the flexible-array member. -Gustavo
On Mon, Mar 30, 2026 at 4:47 PM Gustavo A. R. Silva <gustavo@embeddedor.com> wrote: > > > > On 3/30/26 17:24, Rosen Penev wrote: > > 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. > > Not true. However, it's best practice. > > The requirement is that the _counter_ must be initialized before > the first reference to the flexible-array member. OTOH kzalloc_flex automatically sets it for GCC15 and above. Useful to keep it right after for an eventual coccinelle script... > > -Gustavo
>>>>> 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. >> >> Not true. However, it's best practice. >> >> The requirement is that the _counter_ must be initialized before >> the first reference to the flexible-array member. > OTOH kzalloc_flex automatically sets it for GCC15 and above. Useful to That's what the "it's best practice." comment above alludes to. -Gustavo
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