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

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 7/29/26 2:11 PM, 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 <borntraeger@linux.ibm.com>
> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> ---
>  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;
> +

This would work for the ISM case at least, but I wonder: should we check
vdev->bar_mmap_supported[bar] instead?

My question boils down to: do we still want messages for some of the
cases where we set vdev->bar_mmap_supported[bar] = false in
vfio_pci_probe_mmaps()?

Or should the messages only print when we probed, thought the bar could
be mmap'd (vdev->bar_mmap_supported[bar] == true), and now hit a failure?

Thanks,
Matt

>  		if (!pci_resource_len(pdev, i))
>  			continue;
>