VFIO PCI devices support PMD-sized page table entries for BAR mappings via their huge_fault handler (vfio_pci_mmap_huge_fault). However, the VFIO device file_operations never provided a get_unmapped_area callback to request PMD-aligned virtual address placement from the mmap address allocator. Before commit 34d7cf637c43 ("mm: don't try THP alignment for FS without get_unmapped_area"), this was masked by a bug introduced in commit ed48e87c7df3 ("thp: add thp_get_unmapped_area_vmflags()") which inadvertently applied THP alignment to all file-backed mappings, regardless of whether they provided a get_unmapped_area callback. When commit 34d7cf637c43 ("mm: don't try THP alignment for FS without get_unmapped_area") correctly restricted THP alignment to anonymous mappings and files that explicitly opt in via get_unmapped_area, VFIO BAR mappings lost their PMD-aligned placement. Since the huge_fault handler requires both the VMA start address and the physical PFN to be PMD-aligned, unaligned VMAs force a fallback to 4KB page faults. For example, a 2GiB BAR results in 524,288 individual page faults instead of 1,024 PMD-sized faults, increasing the VFIO_IOMMU_MAP_DMA pinning time by orders of magnitude -- a regression directly visible to KVM guests during PCI device initialization. Fix this by providing a get_unmapped_area callback in vfio_device_fops, following the same pattern used by ext4, xfs, btrfs, fuse, and other subsystems that benefit from THP-aligned placement. Fixes: 34d7cf637c43 ("mm: don't try THP alignment for FS without get_unmapped_area") Cc: stable@vger.kernel.org Cc: Alex Williamson Cc: Kefeng Wang Cc: Vlastimil Babka Cc: Andrew Morton Cc: kvm@vger.kernel.org Signed-off-by: Anthony Pighin --- drivers/vfio/vfio_main.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 6222376ab6ab..2dbb1a84dbac 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -40,6 +40,7 @@ #include #include #include +#include #include "vfio.h" #define DRIVER_VERSION "0.3" @@ -1461,6 +1462,7 @@ const struct file_operations vfio_device_fops = { .unlocked_ioctl = vfio_device_fops_unl_ioctl, .compat_ioctl = compat_ptr_ioctl, .mmap = vfio_device_fops_mmap, + .get_unmapped_area = thp_get_unmapped_area, #ifdef CONFIG_PROC_FS .show_fdinfo = vfio_device_show_fdinfo, #endif -- 2.43.0