Re: [RFC v1 1/2] drivers/vfio_pci_core: Change PXD_ORDER check from switch case to if/else block

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 27/02/2026 à 07:16, Ritesh Harjani (IBM) a écrit :
> Architectures like PowerPC uses runtime defined values for
> PMD_ORDER/PUD_ORDER. This is because it can use either RADIX or HASH MMU
> at runtime using kernel cmdline. So the pXd_index_size is not known at
> compile time. Without this fix, when we add huge pfn support on powerpc
> in the next patch, vfio_pci_core driver compilation can fail with the
> following errors.
> 
>    CC [M]  drivers/vfio/vfio_main.o
>    CC [M]  drivers/vfio/group.o
>    CC [M]  drivers/vfio/container.o
>    CC [M]  drivers/vfio/virqfd.o
>    CC [M]  drivers/vfio/vfio_iommu_spapr_tce.o
>    CC [M]  drivers/vfio/pci/vfio_pci_core.o
>    CC [M]  drivers/vfio/pci/vfio_pci_intrs.o
>    CC [M]  drivers/vfio/pci/vfio_pci_rdwr.o
>    CC [M]  drivers/vfio/pci/vfio_pci_config.o
>    CC [M]  drivers/vfio/pci/vfio_pci.o
>    AR      kernel/built-in.a
> ../drivers/vfio/pci/vfio_pci_core.c: In function ‘vfio_pci_vmf_insert_pfn’:
> ../drivers/vfio/pci/vfio_pci_core.c:1678:9: error: case label does not reduce to an integer constant
>   1678 |         case PMD_ORDER:
>        |         ^~~~
> ../drivers/vfio/pci/vfio_pci_core.c:1682:9: error: case label does not reduce to an integer constant
>   1682 |         case PUD_ORDER:
>        |         ^~~~
> make[6]: *** [../scripts/Makefile.build:289: drivers/vfio/pci/vfio_pci_core.o] Error 1
> make[6]: *** Waiting for unfinished jobs....
> make[5]: *** [../scripts/Makefile.build:546: drivers/vfio/pci] Error 2
> make[5]: *** Waiting for unfinished jobs....
> make[4]: *** [../scripts/Makefile.build:546: drivers/vfio] Error 2
> make[3]: *** [../scripts/Makefile.build:546: drivers] Error 2
> 
> Fixes: f9e54c3a2f5b7 ("vfio/pci: implement huge_fault support")
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> ---
>   drivers/vfio/pci/vfio_pci_core.c | 15 +++++++--------
>   1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index d43745fe4c84..5395a6f30904 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1670,21 +1670,20 @@ vm_fault_t vfio_pci_vmf_insert_pfn(struct vfio_pci_core_device *vdev,
>   	if (vdev->pm_runtime_engaged || !__vfio_pci_memory_enabled(vdev))
>   		return VM_FAULT_SIGBUS;
> 
> -	switch (order) {
> -	case 0:
> +	if (order == 0) {
>   		return vmf_insert_pfn(vmf->vma, vmf->address, pfn);
> +	}

Those braces are unneeded as all legs of the if/else are single lines

>   #ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP

ifdef could be replaced by IS_ENABLED() because PxD_ORDER and 
vmf_insert_pfn_xxx() are declared all the time

> -	case PMD_ORDER:
> +	 else if (order == PMD_ORDER) {

'else' is not needed because every 'if' leads to a return statement

>   		return vmf_insert_pfn_pmd(vmf, pfn, false);
> +	 }
>   #endif
>   #ifdef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
> -	case PUD_ORDER:
> +	 else if (order == PUD_ORDER) {
>   		return vmf_insert_pfn_pud(vmf, pfn, false);
> -		break;
> +	 }
>   #endif
> -	default:
> -		return VM_FAULT_FALLBACK;
> -	}
> +	return VM_FAULT_FALLBACK;

So at the end we should get something like:

	if (!order)
		return vmf_insert_pfn(vmf->vma, vmf->address, pfn);

	if (IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP) && order == PMD_ORDER)
		return vmf_insert_pfn_pmd(vmf, pfn, false);

	if (IS_ENABLED(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP) && order == PMD_ORDER)
		return vmf_insert_pfn_pud(vmf, pfn, false);

	return VM_FAULT_FALLBACK;


>   }
>   EXPORT_SYMBOL_GPL(vfio_pci_vmf_insert_pfn);
> 
> --
> 2.53.0
> 
>