Re: [RFC PATCH v1 06/38] iommufd: Add and option to request for bar mapping with IORESOURCE_EXCLUSIVE

Xu Yilun
2025-07-30T06:52:51Z

> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 6328c3a05bcd..bee3cf3226e9 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1753,8 +1753,15 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma
> * we need to request the region and the barmap tracks that.
> */
> if (!vdev->barmap[index]) {
> - ret = pci_request_selected_regions(pdev,
> +
> + if (core_vdev->iommufd_device &&
> + iommufd_device_need_exclusive_range(core_vdev->iommufd_device))
> + ret = pci_request_selected_regions_exclusive(pdev,
> + 1 << index, "vfio-pci");
> + else
> + ret = pci_request_selected_regions(pdev,
> 1 << index, "vfio-pci");
> +
> if (ret)
> return ret;

I did't get the idea.

The purpose of my original patch [1] is not to make VFIO choose between
pci_request_regions_exclusive() or pci_request_regions(). It is mainly
to prevent userspace mmap/read/write against a vfio_cdev FD. For
example:

If pci_request_selected_regions() is succesfully executed on mmap(),
later TSM Bind would fail on its pci_request_regions_exclusive(). It
means userspace should not mmap otherwise you can't do private
assignment. Vice versa, if you've done TSM Bind, you cannot mmap
anymore.

The _exclusive is just a bonus that further prevents "/dev/mem and the
sysfs MMIO access"

[1]: https://lore.kernel.org/all/20250529053513.1592088-20-yilun.xu@linux.intel.com/

Thanks,
Yilun