Re: [PATCH 1/1] vfio/pci: add PCIe TPH device ioctl

[Wathsala Vithanage <wathsala.vithanage@arm.com>]

On 11/5/25 13:15, Alex Williamson wrote:
> On Mon, 27 Oct 2025 09:33:33 -0500
> Wathsala Vithanage <wathsala.vithanage@arm.com> wrote:
>
>> On 10/16/25 16:41, Jeremy Linton wrote:
>>> Hi,
>>>
>>> On 10/13/25 11:35 AM, Wathsala Vithanage wrote:
>>>> TLP Processing Hints (TPH) let a requester provide steering hints that
>>>> can enable direct cache injection on supported platforms and PCIe
>>>> devices. The PCIe core already exposes TPH handling to kernel drivers.
>>>>
>>>> This change adds the VFIO_DEVICE_PCI_TPH ioctl and exposes TPH control
>>>> to user space to reduce memory latency and improve throughput for
>>>> polling drivers (e.g., DPDK poll-mode drivers). Through this interface,
>>>> user-space drivers can:
>>>>     - enable or disable TPH for the device function
>>>>     - program steering tags in device-specific mode
>>>>
>>>> The ioctl is available only when the device advertises the TPH
>>>> Capability. Invalid modes or tags are rejected. No functional change
>>>> occurs unless the ioctl is used.
>>>>
>>>> Signed-off-by: Wathsala Vithanage <wathsala.vithanage@arm.com>
>>>> ---
>>>>    drivers/vfio/pci/vfio_pci_core.c | 74 ++++++++++++++++++++++++++++++++
>>>>    include/uapi/linux/vfio.h        | 36 ++++++++++++++++
>>>>    2 files changed, 110 insertions(+)
>>>>
>>>> diff --git a/drivers/vfio/pci/vfio_pci_core.c
>>>> b/drivers/vfio/pci/vfio_pci_core.c
>>>> index 7dcf5439dedc..0646d9a483fb 100644
>>>> --- a/drivers/vfio/pci/vfio_pci_core.c
>>>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>>>> @@ -28,6 +28,7 @@
>>>>    #include <linux/nospec.h>
>>>>    #include <linux/sched/mm.h>
>>>>    #include <linux/iommufd.h>
>>>> +#include <linux/pci-tph.h>
>>>>    #if IS_ENABLED(CONFIG_EEH)
>>>>    #include <asm/eeh.h>
>>>>    #endif
>>>> @@ -1443,6 +1444,77 @@ static int vfio_pci_ioctl_ioeventfd(struct
>>>> vfio_pci_core_device *vdev,
>>>>                      ioeventfd.fd);
>>>>    }
>>>>    +static int vfio_pci_tph_set_st(struct vfio_pci_core_device *vdev,
>>>> +                   const struct vfio_pci_tph_entry *ent)
>>>> +{
>>>> +    int ret, mem_type;
>>>> +    u16 st;
>>>> +    u32 cpu_id = ent->cpu_id;
>>>> +
>>>> +    if (cpu_id >= nr_cpu_ids || !cpu_present(cpu_id))
>>>> +        return -EINVAL;
>>>> +
>>>> +    if (!cpumask_test_cpu(cpu_id, current->cpus_ptr))
>>>> +        return -EINVAL;
>>>> +
>>>> +    switch (ent->mem_type) {
>>>> +    case VFIO_TPH_MEM_TYPE_VMEM:
>>>> +        mem_type = TPH_MEM_TYPE_VM;
>>>> +        break;
>>>> +    case VFIO_TPH_MEM_TYPE_PMEM:
>>>> +        mem_type = TPH_MEM_TYPE_PM;
>>>> +        break;
>>>> +    default:
>>>> +        return -EINVAL;
>>>> +    }
>>>> +    ret = pcie_tph_get_cpu_st(vdev->pdev, mem_type,
>>>> topology_core_id(cpu_id),
>>>> +                  &st);
>>>> +    if (ret)
>>>> +        return ret;
>>>> +    /*
>>>> +     * PCI core enforces table bounds and disables TPH on error.
>>>> +     */
>>>> +    return pcie_tph_set_st_entry(vdev->pdev, ent->index, st);
>>>> +}
>>>> +
>>>> +static int vfio_pci_tph_enable(struct vfio_pci_core_device *vdev,
>>>> int mode)
>>>> +{
>>>> +    /* IV mode is not supported. */
>>>> +    if (mode == PCI_TPH_ST_IV_MODE)
>>>> +        return -EINVAL;
>>>> +    /* PCI core validates 'mode' and returns -EINVAL on bad values. */
>>>> +    return pcie_enable_tph(vdev->pdev, mode);
>>>> +}
>>>> +
>>>> +static int vfio_pci_tph_disable(struct vfio_pci_core_device *vdev)
>>>> +{
>>>> +    pcie_disable_tph(vdev->pdev);
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static int vfio_pci_ioctl_tph(struct vfio_pci_core_device *vdev,
>>>> +                  void __user *uarg)
>>>> +{
>>>> +    struct vfio_pci_tph tph;
>>>> +
>>>> +    if (copy_from_user(&tph, uarg, sizeof(struct vfio_pci_tph)))
>>>> +        return -EFAULT;
>>>> +
>>>> +    if (tph.argsz != sizeof(struct vfio_pci_tph))
>>>> +        return -EINVAL;
>>>> +
>>>> +    switch (tph.op) {
>>>> +    case VFIO_DEVICE_TPH_ENABLE:
>>>> +        return vfio_pci_tph_enable(vdev, tph.mode);
>>>> +    case VFIO_DEVICE_TPH_DISABLE:
>>>> +        return vfio_pci_tph_disable(vdev);
>>>> +    case VFIO_DEVICE_TPH_SET_ST:
>>>> +        return vfio_pci_tph_set_st(vdev, &tph.ent);
>>>> +    default:
>>>> +        return -EINVAL;
>>>> +    }
>>>> +}
>>>> +
>>>>    long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned
>>>> int cmd,
>>>>                 unsigned long arg)
>>>>    {
>>>> @@ -1467,6 +1539,8 @@ long vfio_pci_core_ioctl(struct vfio_device
>>>> *core_vdev, unsigned int cmd,
>>>>            return vfio_pci_ioctl_reset(vdev, uarg);
>>>>        case VFIO_DEVICE_SET_IRQS:
>>>>            return vfio_pci_ioctl_set_irqs(vdev, uarg);
>>>> +    case VFIO_DEVICE_PCI_TPH:
>>>> +        return vfio_pci_ioctl_tph(vdev, uarg);
>>>>        default:
>>>>            return -ENOTTY;
>>>>        }
>>>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>>>> index 75100bf009ba..cfdee851031e 100644
>>>> --- a/include/uapi/linux/vfio.h
>>>> +++ b/include/uapi/linux/vfio.h
>>>> @@ -873,6 +873,42 @@ struct vfio_device_ioeventfd {
>>>>      #define VFIO_DEVICE_IOEVENTFD        _IO(VFIO_TYPE, VFIO_BASE + 16)
>>>>    +/**
>>>> + * VFIO_DEVICE_PCI_TPH - _IO(VFIO_TYPE, VFIO_BASE + 22)
>>>> + *
>>>> + * Control PCIe TLP Processing Hints (TPH) on a PCIe device.
>>>> + *
>>>> + * Supported operations:
>>>> + * - VFIO_DEVICE_TPH_ENABLE: enable TPH in no-steering-tag (NS) or
>>>> + *   device-specific (DS) mode. IV mode is not supported via this ioctl
>>>> + *   and returns -EINVAL.
>>>> + * - VFIO_DEVICE_TPH_DISABLE: disable TPH on the device.
>>>> + * - VFIO_DEVICE_TPH_SET_ST: program an entry in the device TPH
>>>> Steering-Tag
>>>> + *   (ST) table. The kernel derives the ST from cpu_id and mem_type;
>>>> the
>>>> + *   value is not returned to userspace.
>>>> + */
>>>> +struct vfio_pci_tph_entry {
>>>> +    __u32 cpu_id;            /* CPU logical ID */
>>>> +    __u8  mem_type;
>>>> +#define VFIO_TPH_MEM_TYPE_VMEM        0   /* Request volatile memory
>>>> ST */
>>>> +#define VFIO_TPH_MEM_TYPE_PMEM        1   /* Request persistent
>>>> memory ST */
>>>> +    __u8  rsvd[1];
>>>> +    __u16 index;            /* ST-table index */
>>>> +};
>>>> +
>>>> +struct vfio_pci_tph {
>>>> +    __u32 argsz;            /* Size of vfio_pci_tph */
>>>> +    __u32 mode;            /* NS and DS modes; IV not supported */
>>>> +    __u32 op;
>>>> +#define VFIO_DEVICE_TPH_ENABLE        0
>>>> +#define VFIO_DEVICE_TPH_DISABLE        1
>>>> +#define VFIO_DEVICE_TPH_SET_ST        2
>>>> +    struct vfio_pci_tph_entry ent;
>>>> +};
>>>> +
>>>> +#define VFIO_DEVICE_PCI_TPH    _IO(VFIO_TYPE, VFIO_BASE + 22)
>>> A quick look at this, it seems its following the way the existing vfio
>>> IOCTls are defined, yet two of them (ENABLE and DISABLE) won't likely
>>> really change their structure, or don't need a structure in the case
>>> of disable. Why not use IOW() and let the kernel error handling deal
>>> with those two as independent ioctls?
>>>
>>>
>>> Thanks,
>>
>> It will require two IOCTLs. I’m ok with having two IOCTLs for this
>> feature if the maintainers are fine with it.
> TBH, I'm not sure why we didn't use a DEVICE_FEATURE for this.  Seems
> like we could implement a SET operation that does enable/disable and

Thanks Alex, it was implemented as a DEVICE_FEATURE in RFC v1,
except it had a GET operation to get the tag to the user; which we
decided to drop.

> another for steering tags.  I still need to fully grasp the
> implications of this support though.  Thanks,
This is now same as the already merged RDMA TPH feature.
https://lore.kernel.org/linux-rdma/cover.1751907231.git.leon@kernel.org/

--wathsala