Re: [PATCH v19 15/18] vfio/pci: Implement TPH_RESOLVE feature for DMABUF and CPU source resolving

[Alex Williamson <alex@shazbot.org>]

On Thu, 2 Jul 2026 20:42:21 +0800
Chengwen Feng <fengchengwen@huawei.com> wrote:

> Add vfio_pci_core_feature_tph_resolve() to implement the
> VFIO_DEVICE_FEATURE_TPH_RESOLVE GET-only uAPI.
> 
> Resolve PH/ST values from two supported sources:
> - DMABUF fd: retrieve stored TPH metadata via dmabuf helper
> - CPU ID: fetch ST tag from platform via PCIe TPH core helper
> 
> Gate supported source types dynamically according to the tph_policy level:
> No-ST/IV modes only permit DMABUF resolution, while DS+ modes additionally
> allow CPU volatile/persistent sources.

RESOLVE is not an oracle, it's not only the sources that can be
resolved, but whether the user has a means to use the value.  RESOLVE
should not return a LITERAL unless the device supports DS mode or
supports IV mode AND we're in POLICY_LITERAL.  Thanks,

Alex

 
> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 75 ++++++++++++++++++++++++++++++++
>  1 file changed, 75 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 14944d3ea86e..ed6bbffa8b26 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1641,6 +1641,78 @@ static int vfio_pci_core_feature_tph(struct vfio_pci_core_device *vdev,
>  	return copy_to_user(arg, &tph, sizeof(tph)) ? -EFAULT : 0;
>  }
>  
> +static int vfio_pci_core_feature_tph_resolve(struct vfio_pci_core_device *vdev,
> +			u32 flags,
> +			struct vfio_device_feature_tph_resolve __user *arg,
> +			size_t argsz)
> +{
> +	const u32 permit_src_mask[] = {
> +		[VFIO_PCI_TPH_POLICY_NO_ST] = VFIO_DEVICE_TPH_SRC_DMABUF,
> +		[VFIO_PCI_TPH_POLICY_IV_ST] = VFIO_DEVICE_TPH_SRC_DMABUF,
> +		[VFIO_PCI_TPH_POLICY_DS_ST ... VFIO_PCI_TPH_POLICY_LITERAL] =
> +					VFIO_DEVICE_TPH_SRC_DMABUF |
> +					VFIO_DEVICE_TPH_SRC_CPU_VOLATILE |
> +					VFIO_DEVICE_TPH_SRC_CPU_PERSISTENT,
> +	};
> +	u32 permit_flags = permit_src_mask[vdev->tph_policy] |
> +			   VFIO_DEVICE_TPH_EXTENDED;
> +	struct vfio_device_feature_tph_resolve resolve = {0};
> +	enum tph_mem_type mtype;
> +	bool extended;
> +	u32 src_bits;
> +	u16 tag = 0;
> +	u8 ph = 0;
> +	int ret;
> +
> +	if (!vdev->tph_permit)
> +		return -EOPNOTSUPP;
> +
> +	ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET,
> +				 sizeof(resolve));
> +	if (ret <= 0)
> +		return ret;
> +
> +	if (copy_from_user(&resolve, arg, sizeof(resolve)))
> +		return -EFAULT;
> +
> +	src_bits = resolve.flags & VFIO_DEVICE_TPH_SRC_MASK;
> +	if (!(resolve.flags & permit_flags) || !is_power_of_2(src_bits))
> +		return -EINVAL;
> +	extended = !!(resolve.flags & VFIO_DEVICE_TPH_EXTENDED);
> +	if (extended && !pcie_tph_supported(vdev->pdev, true))
> +		return -EINVAL;
> +
> +	resolve.valid = 0;
> +	resolve.ph = 0;
> +	resolve.st = 0;
> +
> +	if (src_bits & VFIO_DEVICE_TPH_SRC_DMABUF) {
> +		ret = vfio_pci_dma_buf_get_tph_by_fd(resolve.src, extended,
> +						     &tag, &ph);
> +		if (ret)
> +			return ret;
> +		resolve.ph = ph;
> +		resolve.valid = VFIO_DEVICE_TPH_VALID_PH;
> +		if (vdev->tph_policy >= VFIO_PCI_TPH_POLICY_DS_ST) {
> +			resolve.st = tag;
> +			resolve.valid |= VFIO_DEVICE_TPH_VALID_ST;
> +		}
> +		goto out;
> +	}
> +
> +	mtype = (src_bits & VFIO_DEVICE_TPH_SRC_CPU_VOLATILE) ?
> +			TPH_MEM_TYPE_VM : TPH_MEM_TYPE_PM;
> +	ret = pcie_tph_get_cpu_st_explicit(vdev->pdev, mtype, extended,
> +					   resolve.src, &tag);
> +	if (ret)
> +		return ret;
> +	resolve.valid = VFIO_DEVICE_TPH_VALID_ST;
> +	resolve.st = tag;
> +
> +out:
> +	return copy_to_user(arg, &resolve, sizeof(resolve)) ? -EFAULT : 0;
> +}
> +
>  int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
>  				void __user *arg, size_t argsz)
>  {
> @@ -1661,6 +1733,9 @@ int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
>  		return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz);
>  	case VFIO_DEVICE_FEATURE_TPH:
>  		return vfio_pci_core_feature_tph(vdev, flags, arg, argsz);
> +	case VFIO_DEVICE_FEATURE_TPH_RESOLVE:
> +		return vfio_pci_core_feature_tph_resolve(vdev, flags,
> +							 arg, argsz);
>  	default:
>  		return -ENOTTY;
>  	}