[based on latest akpm/mm-new as of June 12th 2025, commit 19d47edf9] This series enables !MAP_FIXED huge pfnmaps for vfio-pci. Before this series, an userapp in most cases need to be modified to benefit from huge mappings to provide huge size aligned VA using MAP_FIXED. After this series, the userapp can benefit from huge pfnmap automatically after the kernel upgrades, with no userspace modifications. It's still best-effort, because the auto-alignment will require a larger VA range to be allocated via the per-arch allocator, hence if the huge-mapping aligned VA cannot be allocated then it'll still fallback to small mappings like before. However that's really from theory POV: in reality I don't yet know when it'll fail on any 64bits system due to it. So far, only vfio-pci is supported. But the logic should be applicable to all the drivers that support or will support huge pfnmaps. Kudos goes to Jason on the suggestion: https://lore.kernel.org/r/20250530131050.GA233377@xxxxxxxxxx Though instead of refactoring shmem, I found we already have a function we can directly reuse for THP calculations. The idea is fairly simple too, which is to make sure whatever virtual address got returned from an mmap() request of the MMIO BAR regions to be huge-size-aligned with the physical address of the corresponding BARs. It contains minimum mm changes, in reality only to rename and export the THP function that can be reused. That is patch 3. Patch 1 & 2 are trivial small cleanups that I found while I'm looking at this problem. They can even be posted separately if anyone would like me to. Patch 4 is a tunneling needed to wire vfio-pci over to the mmap() operations of vfio_device. Then, patch 5 is the real meat. For testing: besides checkpatch and my daily cross-build harness, unit tests working all fine from either myself [1] (based on another Alex's test program) or Alex, checking the alignments look all sane with mmap(!MAP_FIXED), and huge mappings properly installed. Alex Mastro: please feel free to try this out with your internal tests. The hope is that after this series applied your app should get huge pfnmaps without any changes (with any pgoff specified). Logically there should be minimal dependency on stable branches whenever huge pfnmap is available. Comments welcomed, thanks. [1] https://github.com/xzpeter/clibs/blob/master/misc/vfio-pci-nofix.c [2] https://github.com/awilliam/tests/blob/vfio-pci-device-map-alignment/vfio-pci-device-map-alignment.c Peter Xu (5): mm: Deduplicate mm_get_unmapped_area() mm/hugetlb: Remove prepare_hugepage_range() mm: Rename __thp_get_unmapped_area to mm_get_unmapped_area_aligned vfio: Introduce vfio_device_ops.get_unmapped_area hook vfio-pci: Best-effort huge pfnmaps with !MAP_FIXED mappings arch/loongarch/include/asm/hugetlb.h | 14 ------ arch/mips/include/asm/hugetlb.h | 14 ------ drivers/vfio/pci/vfio_pci.c | 3 ++ drivers/vfio/pci/vfio_pci_core.c | 65 ++++++++++++++++++++++++++++ drivers/vfio/vfio_main.c | 18 ++++++++ fs/hugetlbfs/inode.c | 8 +--- include/asm-generic/hugetlb.h | 8 ---- include/linux/huge_mm.h | 14 +++++- include/linux/hugetlb.h | 6 --- include/linux/vfio.h | 7 +++ include/linux/vfio_pci_core.h | 6 +++ mm/huge_memory.c | 6 ++- mm/mmap.c | 5 +-- 13 files changed, 120 insertions(+), 54 deletions(-) -- 2.49.0
