vfio: Drop vfio_file_iommu_group() stub to fudge around a KVM wart

Drop the vfio_file_iommu_group() stub and instead unconditionally declare the function to fudge around a KVM wart where KVM tries to do symbol_get() on vfio_file_iommu_group() (and other VFIO symbols) even if CONFIG_VFIO=n. Ensuring the symbol is always declared fixes a PPC build error when modules are also disabled, in which case symbol_get() simply points at the address of the symbol (with some attributes shenanigans). Because KVM does symbol_get() instead of directly depending on VFIO, the lack of a fully defined symbol is not problematic (ugly, but "fine"). arch/powerpc/kvm/../../../virt/kvm/vfio.c:89:7: error: attribute declaration must precede definition [-Werror,-Wignored-attributes] fn = symbol_get(vfio_file_iommu_group); ^ include/linux/module.h:805:60: note: expanded from macro 'symbol_get' #define symbol_get(x) ({ extern typeof(x) x __attribute__((weak,visibility("hidden"))); &(x); }) ^ include/linux/vfio.h:294:35: note: previous definition is here static inline struct iommu_group *vfio_file_iommu_group(struct file *file) ^ arch/powerpc/kvm/../../../virt/kvm/vfio.c:89:7: error: attribute declaration must precede definition [-Werror,-Wignored-attributes] fn = symbol_get(vfio_file_iommu_group); ^ include/linux/module.h:805:65: note: expanded from macro 'symbol_get' #define symbol_get(x) ({ extern typeof(x) x __attribute__((weak,visibility("hidden"))); &(x); }) ^ include/linux/vfio.h:294:35: note: previous definition is here static inline struct iommu_group *vfio_file_iommu_group(struct file *file) ^ 2 errors generated. Although KVM is firmly in the wrong (there is zero reason for KVM to build virt/kvm/vfio.c when VFIO is disabled), fudge around the error in VFIO as the stub is unnecessary and doesn't serve its intended purpose (KVM is the only external user of vfio_file_iommu_group()), and there is an in-flight series to clean up the entire KVM<->VFIO interaction, i.e. fixing this in KVM would result in more churn in the long run, and the stub needs to go away regardless.

SCSean Christopherson committed 2 years ago