On Wed, May 06, 2026 at 11:23:19AM -0700, Zhiping Zhang wrote: > On Tue, May 5, 2026 at 11:58 PM fengchengwen <[email protected]> wrote: > > > > > > > On 5/1/2026 4:06 AM, Zhiping Zhang wrote: > > > Add a dma-buf callback that returns raw TPH metadata from the exporter > > > so peer devices can reuse the steering tag and processing hint > > > associated with a VFIO-exported buffer. > > > > > > Add a new VFIO_DEVICE_FEATURE_DMA_BUF_TPH ioctl that takes the fd from > > > VFIO_DEVICE_FEATURE_DMA_BUF along with a steering tag and processing > > > hint, validates the fd is a vfio-exported dma-buf belonging to this > > > device, and stores the TPH values under memory_lock. This keeps the > > > existing VFIO_DEVICE_FEATURE_DMA_BUF uAPI completely unchanged. > > > > > > The user sequences setting TPH on the dma-buf before the importer > > > consumes it. > > > > > > Add an st_width parameter to get_tph() so the exporter can reject > > > steering tags that exceed the consumer's supported width (8 vs 16 bit). > > > When no TPH metadata was supplied, get_tph() returns -EOPNOTSUPP. > > > > > > Signed-off-by: Zhiping Zhang <[email protected]> > > > > > > diff --git a/drivers/vfio/pci/vfio_pci_core.c > > > b/drivers/vfio/pci/vfio_pci_core.c > > > --- a/drivers/vfio/pci/vfio_pci_core.c > > > +++ b/drivers/vfio/pci/vfio_pci_core.c > > > @@ -1534,6 +1534,9 @@ 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 > > > --- a/drivers/vfio/pci/vfio_pci_dmabuf.c > > > +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c > > > @@ -19,6 +19,9 @@ struct vfio_pci_dma_buf { > > > u32 nr_ranges; > > > struct kref kref; > > > struct completion comp; > > > + u16 steering_tag; > > > + u8 ph; > > > + u8 tph_present : 1; > > > u8 revoked : 1; > > > }; > > > > > > @@ -69,6 +72,22 @@ 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; > > > + > > > + if (!priv->tph_present) > > > + return -EOPNOTSUPP; > > > + > > > + if (st_width < 16 && priv->steering_tag > ((1U << st_width) - 1)) > > > + return -EINVAL; > > > > The checker will failed in following cases: > > 1. If the exporter passed 8bit st, and importer support 16bit st, then it > > will pass > > the checker. > > 2. The exporter enabled 16bit st and its st is < 256 (note: the pcie > > protocol doesn't > > restrict 16bit-st must >=256), and importer only support 8bit st, then > > it will also > > pass the checker > > > > Suggest userspace passing both st(8bit) and extend-st(16bit), and importer > > chose the > > right one. > > > > Agreed — 8-bit ST and 16-bit Extended ST are distinct namespaces > (firmware returns > them as separate fields with separate validity bits), so a numeric > range check is insufficient. > For v3 I'll change the uAPI to carry both, gated by a flags field: > > #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; > __u16 steering_tag; /* 8-bit ST */ > __u16 steering_tag_ext; /* 16-bit Extended ST */
I wonder whether `steering_tag` and `steering_tag_ext` can coexist and hold different values at the same time. BTW, please send your patches with diffstat. Thanks > __u8 ph; > __u8 reserved[3]; > }; > > get_tph() then picks the field matching the importer's st_width and > returns -EOPNOTSUPP > if that one isn't valid. > > Thanks, > Zhiping
