Re: [RFC PATCH 3/3] iommufd/tsm: Add tsm_bind/unbind iommufd ioctls

[Alexey Kardashevskiy <aik@amd.com>]

On 3/6/25 03:17, Xu Yilun wrote:
> On Mon, Jun 02, 2025 at 02:52:52PM +1000, Alexey Kardashevskiy wrote:
>>
>>
>> On 1/6/25 02:25, Xu Yilun wrote:
>>>> + * struct iommu_vdevice_id - ioctl(IOMMU_VDEVICE_TSM_BIND/UNBIND)
>>>> + * @size: sizeof(struct iommu_vdevice_id)
>>>> + * @vdevice_id: Object handle for the vDevice. Returned from IOMMU_VDEVICE_ALLOC
>>>> + */
>>>> +struct iommu_vdevice_id {
>>>> +	__u32 size;
>>>> +	__u32 vdevice_id;
>>>> +} __packed;
>>>> +#define IOMMU_VDEVICE_TSM_BIND _IO(IOMMUFD_TYPE, IOMMUFD_CMD_VDEVICE_TSM_BIND)
>>>> +#define IOMMU_VDEVICE_TSM_UNBIND _IO(IOMMUFD_TYPE, IOMMUFD_CMD_VDEVICE_TSM_UNBIND)
>>>
>>> Hello, I see you are talking about the detailed implementation. But
>>> could we firstly address the confusing whether this TSM Bind/Unbind
>>> should be a VFIO uAPI or IOMMUFD uAPI?
>>>
>>> In this thread [1], I was talking about TSM Bind/Unbind affects VFIO
>>> behavior so they cannot be iommufd uAPIs which VFIO is not aware of.
>>
>>
>> What will the host VFIO-PCI driver do differently? I only remember "stop mmaping to the userspace", is that all?
> 
> And do unbind before zapping MMIO.

>> Or, more to the point, what is that exact thing which cannot be done from QEMU? Thanks,
> 
> But kernel don't want incorrect userspace calls crash kernel, e.g. VFIO
> zaps MMIO on TDI bound then KVM just crashes. So you need to check if
> zapping MMIOs are allowed in VFIO, that means VFIO still needs to know
> if device is bound.  Scatter BIND/UNBIND & other device controls in both
> IOMMUFD & VFIO makes life harder.

I am confused. What is that userspace call, ioctl(VFIO_DEVICE_RESET)? The userspace (==QEMU) knows it is bound and can unbind first, no?

If it is the case of killing QEMU - then there is no usespace and then it is a matter of what fd is closed first - VFIO-PCI or IOMMUFD, we could teach IOMMUFD to hold an VFIO-PCI fd to guarantee the order. Thanks,



> 
> Thanks,
> Yilun

-- 
Alexey