Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

On Wed, 2026-07-29 at 11:11 -0700, Farhan Ali wrote:
> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
> all devices support having their BARs mapped by the CPU. The
> non_mappable_bars flag indicates that a PCI device's BARs cannot be
> accessed by the CPU. The ISM device on s390 is one such device. The BAR
> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
> to warnings:
> 
> vmalloc_node_range for size 281474976714752 failed: Address range
> restricted to 0x2110bab00000 - 0x21903ab00000
> 
> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
> is set by the PCI core at enumeration time and already serves the same
> purpose in vfio_pci_probe_mmaps().
> 
> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
> Reported-by: Christian Borntraeger <[email protected]>
> Signed-off-by: Farhan Ali <[email protected]>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 3f11a9624b9c..6a184588ff23 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
>  
>  		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
>  
> +		if (pdev->non_mappable_bars)
> +			continue;
> +
>  		if (!pci_resource_len(pdev, i))
>  			continue;
>  

While I was following the discussion I forgot to reply. This looks good
to me. Thank you for taking care of this. 

Feel free to add:

Reviewed-by: Niklas Schnelle <[email protected]>