RE: [PATCH 11/12] mm: Remove callers of pfn_t functionality

Michael Kelley
2025-06-02T04:44:09Z

From: Alistair Popple <apopple@nvidia.com> Sent: Wednesday, May 28, 2025 11:32 PM
>
> All PFN_* pfn_t flags have been removed. Therefore there is no longer
> a need for the pfn_t type and all uses can be replaced with normal
> pfns.
>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/x86/mm/pat/memtype.c | 6 +-
> drivers/dax/device.c | 23 +++----
> drivers/dax/hmem/hmem.c | 1 +-
> drivers/dax/kmem.c | 1 +-
> drivers/dax/pmem.c | 1 +-
> drivers/dax/super.c | 3 +-
> drivers/gpu/drm/exynos/exynos_drm_gem.c | 1 +-
> drivers/gpu/drm/gma500/fbdev.c | 3 +-
> drivers/gpu/drm/i915/gem/i915_gem_mman.c | 1 +-
> drivers/gpu/drm/msm/msm_gem.c | 1 +-
> drivers/gpu/drm/omapdrm/omap_gem.c | 6 +--
> drivers/gpu/drm/v3d/v3d_bo.c | 1 +-
> drivers/hwtracing/intel_th/msu.c | 3 +-
> drivers/md/dm-linear.c | 2 +-
> drivers/md/dm-log-writes.c | 2 +-
> drivers/md/dm-stripe.c | 2 +-
> drivers/md/dm-target.c | 2 +-
> drivers/md/dm-writecache.c | 11 +--
> drivers/md/dm.c | 2 +-
> drivers/nvdimm/pmem.c | 8 +--
> drivers/nvdimm/pmem.h | 4 +-
> drivers/s390/block/dcssblk.c | 9 +--
> drivers/vfio/pci/vfio_pci_core.c | 5 +-
> fs/cramfs/inode.c | 5 +-
> fs/dax.c | 50 +++++++--------
> fs/ext4/file.c | 2 +-
> fs/fuse/dax.c | 3 +-
> fs/fuse/virtio_fs.c | 5 +-
> fs/xfs/xfs_file.c | 2 +-
> include/linux/dax.h | 9 +--
> include/linux/device-mapper.h | 2 +-
> include/linux/huge_mm.h | 6 +-
> include/linux/mm.h | 4 +-
> include/linux/pfn.h | 9 +---
> include/linux/pfn_t.h | 85 +-------------------------
> include/linux/pgtable.h | 4 +-
> include/trace/events/fs_dax.h | 12 +---
> mm/debug_vm_pgtable.c | 1 +-
> mm/huge_memory.c | 27 +++-----
> mm/memory.c | 31 ++++-----
> mm/memremap.c | 1 +-
> mm/migrate.c | 1 +-
> tools/testing/nvdimm/pmem-dax.c | 6 +-
> tools/testing/nvdimm/test/iomap.c | 7 +--
> tools/testing/nvdimm/test/nfit_test.h | 1 +-
> 45 files changed, 121 insertions(+), 250 deletions(-)
> delete mode 100644 include/linux/pfn_t.h
>

[snip]

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c5345ee..12d9665 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3644,9 +3644,9 @@ vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
> vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
> unsigned long pfn, pgprot_t pgprot);
> vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
> - pfn_t pfn);
> + unsigned long pfn);
> vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
> - unsigned long addr, pfn_t pfn);
> + unsigned long addr, unsigned long pfn);
> int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len);
>
> static inline vm_fault_t vmf_insert_page(struct vm_area_struct *vma,

[snip]

> diff --git a/mm/memory.c b/mm/memory.c
> index 6b03771..4eaf444 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2635,7 +2634,7 @@ EXPORT_SYMBOL(vmf_insert_mixed);
> * the same entry was actually inserted.
> */
> vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
> - unsigned long addr, pfn_t pfn)
> + unsigned long addr, unsigned long pfn)
> {
> return __vm_insert_mixed(vma, addr, pfn, true);
> }

vmf_insert_mixed_mkwrite() is not used anywhere in the
kernel. The commit message for cd1e0dac3a3e suggests it was
originally used by DAX code, so presumably it could just go away.

On the flip side, I have a patch set in flight (see Patch 3 of [1])
that uses it to do mkwrite on a special PTE, and my usage
requires passing PFN_SPECIAL in order to pass the tests in
vm_mixed_ok(). But this may be dubious usage, and should not
be a blocker to your elimination of pfn_t. I'll either add
vmf_insert_special_mkwrite() or figure out an equivalent. Anyone
with suggestions in that direction would be appreciated as I'm
not an mm expert.

Michael

[1] https://lore.kernel.org/linux-hyperv/20250523161522.409504-1-mhklinux@outlook.com/