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

[fengchengwen <fengchengwen@huawei.com>]

On 7/9/2026 7:31 AM, Alex Williamson wrote:
> 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,

Got it. My current RESOLVE logic only filters allowed sources by policy,
but does not check whether the device can actually use the resolved ST.

I will fix it: ST will only be reported when the hardware supports IV/DS
ST table capability, even under LITERAL policy.

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;
>>  	}
>