On Tue, 26 May 2026 07:43:55 -0700 Zhiping Zhang <[email protected]> wrote:
> Implement the dma-buf get_tph callback for vfio-pci-exported dma-bufs > and add VFIO_DEVICE_FEATURE_DMA_BUF_TPH so userspace can attach TPH > metadata to such a dma-buf. > > 8-bit ST and 16-bit Extended ST are distinct PCIe TPH namespaces; the > uAPI carries both with explicit validity flags, and get_tph() returns > the value matching the importer's requested width (or -EOPNOTSUPP). > > The TPH descriptor is published under a new per-dma-buf mutex > (priv->lock) and read by get_tph() under the same mutex. The same > mutex serialises with the priv->vdev clear in > vfio_pci_dma_buf_cleanup() so a SET racing with device teardown > cannot observe a half-detached dma-buf. memory_lock remain on the > existing dma-buf paths; the outer order is memory_lock -> priv->lock. > > Signed-off-by: Zhiping Zhang <[email protected]> > --- > drivers/vfio/pci/vfio_pci_core.c | 3 + > drivers/vfio/pci/vfio_pci_dmabuf.c | 110 ++++++++++++++++++++++++++++- > drivers/vfio/pci/vfio_pci_priv.h | 12 ++++ > include/uapi/linux/vfio.h | 37 ++++++++++ > 4 files changed, 161 insertions(+), 1 deletion(-) > > diff --git a/drivers/vfio/pci/vfio_pci_core.c > b/drivers/vfio/pci/vfio_pci_core.c > index 050e7542952e..4fa36f2f7555 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -1569,6 +1569,9 @@ int vfio_pci_core_ioctl_feature(struct vfio_device > *device, u32 flags, > return vfio_pci_core_feature_token(vdev, flags, arg, argsz); > case VFIO_DEVICE_FEATURE_DMA_BUF: > return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz); > + case VFIO_DEVICE_FEATURE_DMA_BUF_TPH: > + return vfio_pci_core_feature_dma_buf_tph(vdev, flags, arg, > + argsz); > default: > return -ENOTTY; > } > diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c > b/drivers/vfio/pci/vfio_pci_dmabuf.c > index 1a177ce7de54..3ea2978c376c 100644 > --- a/drivers/vfio/pci/vfio_pci_dmabuf.c > +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c > @@ -19,7 +19,19 @@ struct vfio_pci_dma_buf { > u32 nr_ranges; > struct kref kref; > struct completion comp; > - u8 revoked : 1; > + /* > + * @lock serializes TPH SET vs get_tph and the priv->vdev clear in > + * vfio_pci_dma_buf_cleanup(). It nests inside memory_lock: > + * the outer order across these paths is > + * memory_lock -> priv->lock. > + */ > + struct mutex lock; > + u8 tph_st_valid:1; /* priv->lock */ > + u8 tph_st_ext_valid:1; /* priv->lock */ > + u8 tph_ph:2; /* priv->lock */ > + u8 tph_st; /* priv->lock */ > + u16 tph_st_ext; /* priv->lock */ > + u8 revoked:1; /* dma_resv_lock */ > }; > > static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf, > @@ -69,6 +81,38 @@ vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment, > return ret; > } > > +static int vfio_pci_dma_buf_get_tph(struct dma_buf *dmabuf, u16 > *steering_tag, > + u8 *ph, u8 st_width) > +{ > + struct vfio_pci_dma_buf *priv = dmabuf->priv; > + int ret = 0; > + > + mutex_lock(&priv->lock); Use guard semantics and drop ret, return from the error branch directly. > + switch (st_width) { > + case 8: > + if (!priv->tph_st_valid) { > + ret = -EOPNOTSUPP; > + break; > + } > + *steering_tag = priv->tph_st; > + *ph = priv->tph_ph; > + break; > + case 16: > + if (!priv->tph_st_ext_valid) { > + ret = -EOPNOTSUPP; > + break; > + } > + *steering_tag = priv->tph_st_ext; > + *ph = priv->tph_ph; > + break; > + default: > + ret = -EINVAL; > + break; > + } > + mutex_unlock(&priv->lock); > + return ret; > +} > + > static void vfio_pci_dma_buf_unmap(struct dma_buf_attachment *attachment, > struct sg_table *sgt, > enum dma_data_direction dir) > @@ -95,12 +139,14 @@ static void vfio_pci_dma_buf_release(struct dma_buf > *dmabuf) > up_write(&priv->vdev->memory_lock); > vfio_device_put_registration(&priv->vdev->vdev); > } > + mutex_destroy(&priv->lock); > kfree(priv->phys_vec); > kfree(priv); > } > > static const struct dma_buf_ops vfio_pci_dmabuf_ops = { > .attach = vfio_pci_dma_buf_attach, > + .get_tph = vfio_pci_dma_buf_get_tph, > .map_dma_buf = vfio_pci_dma_buf_map, > .unmap_dma_buf = vfio_pci_dma_buf_unmap, > .release = vfio_pci_dma_buf_release, > @@ -265,6 +311,7 @@ int vfio_pci_core_feature_dma_buf(struct > vfio_pci_core_device *vdev, u32 flags, > ret = -ENOMEM; > goto err_free_ranges; > } > + mutex_init(&priv->lock); > priv->phys_vec = kzalloc_objs(*priv->phys_vec, get_dma_buf.nr_ranges); > if (!priv->phys_vec) { > ret = -ENOMEM; > @@ -327,12 +374,71 @@ int vfio_pci_core_feature_dma_buf(struct > vfio_pci_core_device *vdev, u32 flags, > err_free_phys: > kfree(priv->phys_vec); > err_free_priv: > + mutex_destroy(&priv->lock); > kfree(priv); > err_free_ranges: > kfree(dma_ranges); > return ret; > } > > +int vfio_pci_core_feature_dma_buf_tph(struct vfio_pci_core_device *vdev, > + u32 flags, > + struct vfio_device_feature_dma_buf_tph > __user *arg, > + size_t argsz) > +{ > + struct vfio_device_feature_dma_buf_tph set_tph; > + struct vfio_pci_dma_buf *priv; > + struct dma_buf *dmabuf; > + int ret; > + > + ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_SET, > + sizeof(set_tph)); > + if (ret != 1) > + return ret; Don't we need to test whether the device supports the TPH capability somewhere here? AIUI the device must exposed a TPH capability to act as a TPH completer. > + > + if (copy_from_user(&set_tph, arg, sizeof(set_tph))) > + return -EFAULT; > + > + if (set_tph.flags & ~(VFIO_DMA_BUF_TPH_ST | VFIO_DMA_BUF_TPH_ST_EXT)) > + return -EINVAL; > + > + if (!set_tph.flags) > + return -EINVAL; This seems to block the path to marking both steering tags to invalid without any particular reason to do so. > + > + /* PCIe TLP Processing Hint is a 2-bit field. */ > + if (set_tph.ph & ~0x3) > + return -EINVAL; > + > + dmabuf = dma_buf_get(set_tph.dmabuf_fd); > + if (IS_ERR(dmabuf)) > + return PTR_ERR(dmabuf); > + > + if (dmabuf->ops != &vfio_pci_dmabuf_ops) { > + ret = -EINVAL; > + goto out_put; > + } > + > + priv = dmabuf->priv; > + mutex_lock(&priv->lock); Use guards. > + if (priv->vdev != vdev) { For here and the next chunk, why is priv->vdev pulled into this lock? We're calling an ioctl on the vdev, that's stable. We have a reference to the dma-buf, that's stable. I think the ordering prevents this from needing to be under the lock, which probably means it should be s/lock/tph_lock/. > + ret = -EINVAL; > + goto out_unlock; > + } > + > + priv->tph_st = set_tph.steering_tag; > + priv->tph_st_ext = set_tph.steering_tag_ext; > + priv->tph_ph = set_tph.ph; > + priv->tph_st_valid = !!(set_tph.flags & VFIO_DMA_BUF_TPH_ST); > + priv->tph_st_ext_valid = !!(set_tph.flags & VFIO_DMA_BUF_TPH_ST_EXT); > + ret = 0; > + > +out_unlock: > + mutex_unlock(&priv->lock); > +out_put: > + dma_buf_put(dmabuf); > + return ret; > +} > + > void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked) > { > struct vfio_pci_dma_buf *priv; > @@ -398,7 +504,9 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device > *vdev) > continue; > > list_del_init(&priv->dmabufs_elm); > + mutex_lock(&priv->lock); > priv->vdev = NULL; > + mutex_unlock(&priv->lock); As above, seems unnecessary. > vfio_device_put_registration(&vdev->vdev); > fput(priv->dmabuf->file); > } > diff --git a/drivers/vfio/pci/vfio_pci_priv.h > b/drivers/vfio/pci/vfio_pci_priv.h > index fca9d0dfac90..c58f369be4b3 100644 > --- a/drivers/vfio/pci/vfio_pci_priv.h > +++ b/drivers/vfio/pci/vfio_pci_priv.h > @@ -118,6 +118,10 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev) > int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 > flags, > struct vfio_device_feature_dma_buf __user > *arg, > size_t argsz); > +int vfio_pci_core_feature_dma_buf_tph(struct vfio_pci_core_device *vdev, > + u32 flags, > + struct vfio_device_feature_dma_buf_tph > __user *arg, > + size_t argsz); > void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev); > void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked); > #else > @@ -128,6 +132,14 @@ vfio_pci_core_feature_dma_buf(struct > vfio_pci_core_device *vdev, u32 flags, > { > return -ENOTTY; > } > + > +static inline int > +vfio_pci_core_feature_dma_buf_tph(struct vfio_pci_core_device *vdev, u32 > flags, > + struct vfio_device_feature_dma_buf_tph __user > *arg, > + size_t argsz) > +{ > + return -ENOTTY; > +} > static inline void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device > *vdev) > { > } > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > index 5de618a3a5ee..55cac3b7122c 100644 > --- a/include/uapi/linux/vfio.h > +++ b/include/uapi/linux/vfio.h > @@ -1534,6 +1534,43 @@ struct vfio_device_feature_dma_buf { > */ > #define VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2 12 > > +/** > + * Upon VFIO_DEVICE_FEATURE_SET associate TPH (TLP Processing Hints) metadata > + * with a vfio-exported dma-buf. The dma-buf must have been created by > + * VFIO_DEVICE_FEATURE_DMA_BUF on this device. > + * > + * dmabuf_fd is the file descriptor returned by VFIO_DEVICE_FEATURE_DMA_BUF. > + * > + * 8-bit ST (steering_tag) and 16-bit Extended ST (steering_tag_ext) are > + * distinct namespaces in the PCIe TPH ST table and may both be present with > + * different values. Userspace should populate the value(s) it has from the > + * firmware ST table for this device and set the matching > VFIO_DMA_BUF_TPH_ST / > + * VFIO_DMA_BUF_TPH_ST_EXT bit in @flags. An importer requests a specific > + * width and receives the matching value; if the requested width is not > + * present, the importer is told TPH is unavailable for this dma-buf. > + * > + * ph is the 2-bit TLP Processing Hint and must be in the range [0, 3]. > + * > + * Userspace is responsible for setting TPH on the dma-buf before handing the > + * fd to the importer. Calling SET again replaces the previously published > + * values; racing a SET against an importer that is already consuming the > + * dma-buf is a userspace ordering problem. > + * > + * Return: 0 on success, -errno on failure. > + */ > +#define VFIO_DEVICE_FEATURE_DMA_BUF_TPH 13 > + > +#define VFIO_DMA_BUF_TPH_ST (1 << 0) /* steering_tag valid */ > +#define VFIO_DMA_BUF_TPH_ST_EXT (1 << 1) /* steering_tag_ext > valid */ > + > +struct vfio_device_feature_dma_buf_tph { > + __s32 dmabuf_fd; > + __u32 flags; > + __u8 steering_tag; > + __u8 ph; Nit, I'd swap the order of these so the steering_tag fields are back-to-back. Thanks, Alex
