[PATCH v2 01/14] mm: Convert pXd_devmap checks to vma_is_dax
From: Alistair Popple <apopple@nvidia.com>
Date: 2025-06-16 11:58:42
Also in:
dri-devel, linux-arm-kernel, linux-cxl, linux-ext4, linux-fsdevel, linux-mm, linux-riscv, linux-xfs, lkml, loongarch, nvdimm
Subsystem:
filesystems (vfs and infrastructure), hmm - heterogeneous memory management, memory management, memory management - userfaultfd, the rest · Maintainers:
Alexander Viro, Christian Brauner, Jason Gunthorpe, Leon Romanovsky, Andrew Morton, Mike Rapoport, Linus Torvalds
Currently dax is the only user of pmd and pud mapped ZONE_DEVICE pages. Therefore page walkers that want to exclude DAX pages can check pmd_devmap or pud_devmap. However soon dax will no longer set PFN_DEV, meaning dax pages are mapped as normal pages. Ensure page walkers that currently use pXd_devmap to skip DAX pages continue to do so by adding explicit checks of the VMA instead. Signed-off-by: Alistair Popple <apopple@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Dan Williams <redacted> --- Changes from v1: - Remove vma_is_dax() check from mm/userfaultfd.c as validate_move_areas() will already skip DAX VMA's on account of them not being anonymous. --- fs/userfaultfd.c | 2 +- mm/hmm.c | 2 +- mm/userfaultfd.c | 6 ------ 3 files changed, 2 insertions(+), 8 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index ef054b3..a886750 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c@@ -304,7 +304,7 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, goto out; ret = false; - if (!pmd_present(_pmd) || pmd_devmap(_pmd)) + if (!pmd_present(_pmd) || vma_is_dax(vmf->vma)) goto out; if (pmd_trans_huge(_pmd)) {
diff --git a/mm/hmm.c b/mm/hmm.c
index feac861..5311753 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c@@ -441,7 +441,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, return hmm_vma_walk_hole(start, end, -1, walk); } - if (pud_leaf(pud) && pud_devmap(pud)) { + if (pud_leaf(pud) && vma_is_dax(walk->vma)) { unsigned long i, npages, pfn; unsigned int required_fault; unsigned long *hmm_pfns;
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 58b3ad6..8395db2 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c@@ -1818,12 +1818,6 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, ptl = pmd_trans_huge_lock(src_pmd, src_vma); if (ptl) { - if (pmd_devmap(*src_pmd)) { - spin_unlock(ptl); - err = -ENOENT; - break; - } - /* Check if we can move the pmd without splitting it. */ if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || !pmd_none(dst_pmdval)) {
--
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