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

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Message-ID: <aIm/EFCoGdNmhaou@yilunxu-OptiPlex-7050>
Date: Wed, 30 Jul 2025 14:43:28 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org>
Cc: linux-coco@...ts.linux.dev, kvmarm@...ts.linux.dev,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	aik@....com, lukas@...ner.de, Samuel Ortiz <sameo@...osinc.com>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Suzuki K Poulose <Suzuki.Poulose@....com>,
	Steven Price <steven.price@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>
Subject: Re: [RFC PATCH v1 06/38] iommufd: Add and option to request for bar
 mapping with IORESOURCE_EXCLUSIVE

> 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