The patch titled
Subject: mm/gup: handle hugepd for follow_page()
has been added to the -mm mm-unstable branch. Its filename is
mm-gup-handle-hugepd-for-follow_page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gup-handle-hugepd-for-follow_page.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm/gup: handle hugepd for follow_page()
Date: Wed, 27 Mar 2024 11:23:31 -0400
Hugepd is only used in PowerPC so far on 4K page size kernels where hash
mmu is used. follow_page_mask() used to leverage hugetlb APIs to access
hugepd entries. Teach follow_page_mask() itself on hugepd.
With previous refactors on fast-gup gup_huge_pd(), most of the code can be
leveraged. There's something not needed for follow page, for example,
gup_hugepte() tries to detect pgtable entry change which will never happen
with slow gup (which has the pgtable lock held), but that's not a problem
to check.
Since follow_page() always only fetch one page, set the end to "address +
PAGE_SIZE" should suffice. We will still do the pgtable walk once for
each hugetlb page by setting ctx->page_mask properly.
One thing worth mentioning is that some level of pgtable's _bad() helper
will report is_hugepd() entries as TRUE on Power8 hash MMUs. I think it
at least applies to PUD on Power8 with 4K pgsize. It means feeding a
hugepd entry to pud_bad() will report a false positive. Let's leave that
for now because it can be arch-specific where I am a bit declined to
touch. In this patch it's not a problem as long as hugepd is detected
before any bad pgtable entries.
To allow slow gup like follow_*_page() to access hugepd helpers, hugepd
codes are moved to the top. Besides that, the helper record_subpages()
will be used by either hugepd or fast-gup now. To avoid "unused function"
warnings we must provide a "#ifdef" for it, unfortunately.
Link: https://lkml.kernel.org/r/20240327152332.950956-13-peterx@xxxxxxxxxx
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andrew Jones <andrew.jones@xxxxxxxxx>
Cc: Aneesh Kumar K.V (IBM) <aneesh.kumar@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 269 ++++++++++++++++++++++++++++++++---------------------
1 file changed, 163 insertions(+), 106 deletions(-)
--- a/mm/gup.c~mm-gup-handle-hugepd-for-follow_page
+++ a/mm/gup.c
@@ -500,6 +500,149 @@ static inline void mm_set_has_pinned_fla
}
#ifdef CONFIG_MMU
+
+#if defined(CONFIG_ARCH_HAS_HUGEPD) || defined(CONFIG_HAVE_FAST_GUP)
+static int record_subpages(struct page *page, unsigned long sz,
+ unsigned long addr, unsigned long end,
+ struct page **pages)
+{
+ struct page *start_page;
+ int nr;
+
+ start_page = nth_page(page, (addr & (sz - 1)) >> PAGE_SHIFT);
+ for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
+ pages[nr] = nth_page(start_page, nr);
+
+ return nr;
+}
+#endif /* CONFIG_ARCH_HAS_HUGEPD || CONFIG_HAVE_FAST_GUP */
+
+#ifdef CONFIG_ARCH_HAS_HUGEPD
+static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
+ unsigned long sz)
+{
+ unsigned long __boundary = (addr + sz) & ~(sz-1);
+ return (__boundary - 1 < end - 1) ? __boundary : end;
+}
+
+static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
+ unsigned long end, unsigned int flags,
+ struct page **pages, int *nr)
+{
+ unsigned long pte_end;
+ struct page *page;
+ struct folio *folio;
+ pte_t pte;
+ int refs;
+
+ pte_end = (addr + sz) & ~(sz-1);
+ if (pte_end < end)
+ end = pte_end;
+
+ pte = huge_ptep_get(ptep);
+
+ if (!pte_access_permitted(pte, flags & FOLL_WRITE))
+ return 0;
+
+ /* hugepages are never "special" */
+ VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+
+ page = pte_page(pte);
+ refs = record_subpages(page, sz, addr, end, pages + *nr);
+
+ folio = try_grab_folio(page, refs, flags);
+ if (!folio)
+ return 0;
+
+ if (unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) {
+ gup_put_folio(folio, refs, flags);
+ return 0;
+ }
+
+ if (!pte_write(pte) && gup_must_unshare(NULL, flags, &folio->page)) {
+ gup_put_folio(folio, refs, flags);
+ return 0;
+ }
+
+ *nr += refs;
+ folio_set_referenced(folio);
+ return 1;
+}
+
+/*
+ * NOTE: currently GUP for a hugepd is only possible on hugetlbfs file
+ * systems on Power, which does not have issue with folio writeback against
+ * GUP updates. When hugepd will be extended to support non-hugetlbfs or
+ * even anonymous memory, we need to do extra check as what we do with most
+ * of the other folios. See writable_file_mapping_allowed() and
+ * folio_fast_pin_allowed() for more information.
+ */
+static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
+ unsigned int pdshift, unsigned long end, unsigned int flags,
+ struct page **pages, int *nr)
+{
+ pte_t *ptep;
+ unsigned long sz = 1UL << hugepd_shift(hugepd);
+ unsigned long next;
+
+ ptep = hugepte_offset(hugepd, addr, pdshift);
+ do {
+ next = hugepte_addr_end(addr, end, sz);
+ if (!gup_hugepte(ptep, sz, addr, end, flags, pages, nr))
+ return 0;
+ } while (ptep++, addr = next, addr != end);
+
+ return 1;
+}
+
+static struct page *follow_hugepd(struct vm_area_struct *vma, hugepd_t hugepd,
+ unsigned long addr, unsigned int pdshift,
+ unsigned int flags,
+ struct follow_page_context *ctx)
+{
+ struct page *page;
+ struct hstate *h;
+ spinlock_t *ptl;
+ int nr = 0, ret;
+ pte_t *ptep;
+
+ /* Only hugetlb supports hugepd */
+ if (WARN_ON_ONCE(!is_vm_hugetlb_page(vma)))
+ return ERR_PTR(-EFAULT);
+
+ h = hstate_vma(vma);
+ ptep = hugepte_offset(hugepd, addr, pdshift);
+ ptl = huge_pte_lock(h, vma->vm_mm, ptep);
+ ret = gup_huge_pd(hugepd, addr, pdshift, addr + PAGE_SIZE,
+ flags, &page, &nr);
+ spin_unlock(ptl);
+
+ if (ret) {
+ WARN_ON_ONCE(nr != 1);
+ ctx->page_mask = (1U << huge_page_order(h)) - 1;
+ return page;
+ }
+
+ return NULL;
+}
+#else /* CONFIG_ARCH_HAS_HUGEPD */
+static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
+ unsigned int pdshift, unsigned long end, unsigned int flags,
+ struct page **pages, int *nr)
+{
+ return 0;
+}
+
+static struct page *follow_hugepd(struct vm_area_struct *vma, hugepd_t hugepd,
+ unsigned long addr, unsigned int pdshift,
+ unsigned int flags,
+ struct follow_page_context *ctx)
+{
+ return NULL;
+}
+#endif /* CONFIG_ARCH_HAS_HUGEPD */
+
+
static struct page *no_page_table(struct vm_area_struct *vma,
unsigned int flags, unsigned long address)
{
@@ -871,6 +1014,9 @@ static struct page *follow_pmd_mask(stru
return no_page_table(vma, flags, address);
if (!pmd_present(pmdval))
return no_page_table(vma, flags, address);
+ if (unlikely(is_hugepd(__hugepd(pmd_val(pmdval)))))
+ return follow_hugepd(vma, __hugepd(pmd_val(pmdval)),
+ address, PMD_SHIFT, flags, ctx);
if (pmd_devmap(pmdval)) {
ptl = pmd_lock(mm, pmd);
page = follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap);
@@ -921,6 +1067,9 @@ static struct page *follow_pud_mask(stru
pud = READ_ONCE(*pudp);
if (!pud_present(pud))
return no_page_table(vma, flags, address);
+ if (unlikely(is_hugepd(__hugepd(pud_val(pud)))))
+ return follow_hugepd(vma, __hugepd(pud_val(pud)),
+ address, PUD_SHIFT, flags, ctx);
if (pud_leaf(pud)) {
ptl = pud_lock(mm, pudp);
page = follow_huge_pud(vma, address, pudp, flags, ctx);
@@ -944,10 +1093,13 @@ static struct page *follow_p4d_mask(stru
p4dp = p4d_offset(pgdp, address);
p4d = READ_ONCE(*p4dp);
- if (!p4d_present(p4d))
- return no_page_table(vma, flags, address);
BUILD_BUG_ON(p4d_leaf(p4d));
- if (unlikely(p4d_bad(p4d)))
+
+ if (unlikely(is_hugepd(__hugepd(p4d_val(p4d)))))
+ return follow_hugepd(vma, __hugepd(p4d_val(p4d)),
+ address, P4D_SHIFT, flags, ctx);
+
+ if (!p4d_present(p4d) || p4d_bad(p4d))
return no_page_table(vma, flags, address);
return follow_pud_mask(vma, address, p4dp, flags, ctx);
@@ -997,10 +1149,15 @@ static struct page *follow_page_mask(str
pgd = pgd_offset(mm, address);
- if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
- return no_page_table(vma, flags, address);
+ if (unlikely(is_hugepd(__hugepd(pgd_val(*pgd)))))
+ page = follow_hugepd(vma, __hugepd(pgd_val(*pgd)),
+ address, PGDIR_SHIFT, flags, ctx);
+ else if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+ page = no_page_table(vma, flags, address);
+ else
+ page = follow_p4d_mask(vma, address, pgd, flags, ctx);
- return follow_p4d_mask(vma, address, pgd, flags, ctx);
+ return page;
}
struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
@@ -2955,106 +3112,6 @@ static int __gup_device_huge_pud(pud_t p
}
#endif
-static int record_subpages(struct page *page, unsigned long sz,
- unsigned long addr, unsigned long end,
- struct page **pages)
-{
- struct page *start_page;
- int nr;
-
- start_page = nth_page(page, (addr & (sz - 1)) >> PAGE_SHIFT);
- for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
- pages[nr] = nth_page(start_page, nr);
-
- return nr;
-}
-
-#ifdef CONFIG_ARCH_HAS_HUGEPD
-static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
- unsigned long sz)
-{
- unsigned long __boundary = (addr + sz) & ~(sz-1);
- return (__boundary - 1 < end - 1) ? __boundary : end;
-}
-
-static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
- unsigned long end, unsigned int flags,
- struct page **pages, int *nr)
-{
- unsigned long pte_end;
- struct page *page;
- struct folio *folio;
- pte_t pte;
- int refs;
-
- pte_end = (addr + sz) & ~(sz-1);
- if (pte_end < end)
- end = pte_end;
-
- pte = huge_ptep_get(ptep);
-
- if (!pte_access_permitted(pte, flags & FOLL_WRITE))
- return 0;
-
- /* hugepages are never "special" */
- VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
-
- page = pte_page(pte);
- refs = record_subpages(page, sz, addr, end, pages + *nr);
-
- folio = try_grab_folio(page, refs, flags);
- if (!folio)
- return 0;
-
- if (unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) {
- gup_put_folio(folio, refs, flags);
- return 0;
- }
-
- if (!pte_write(pte) && gup_must_unshare(NULL, flags, &folio->page)) {
- gup_put_folio(folio, refs, flags);
- return 0;
- }
-
- *nr += refs;
- folio_set_referenced(folio);
- return 1;
-}
-
-/*
- * NOTE: currently GUP for a hugepd is only possible on hugetlbfs file
- * systems on Power, which does not have issue with folio writeback against
- * GUP updates. When hugepd will be extended to support non-hugetlbfs or
- * even anonymous memory, we need to do extra check as what we do with most
- * of the other folios. See writable_file_mapping_allowed() and
- * folio_fast_pin_allowed() for more information.
- */
-static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
- unsigned int pdshift, unsigned long end, unsigned int flags,
- struct page **pages, int *nr)
-{
- pte_t *ptep;
- unsigned long sz = 1UL << hugepd_shift(hugepd);
- unsigned long next;
-
- ptep = hugepte_offset(hugepd, addr, pdshift);
- do {
- next = hugepte_addr_end(addr, end, sz);
- if (!gup_hugepte(ptep, sz, addr, end, flags, pages, nr))
- return 0;
- } while (ptep++, addr = next, addr != end);
-
- return 1;
-}
-#else
-static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
- unsigned int pdshift, unsigned long end, unsigned int flags,
- struct page **pages, int *nr)
-{
- return 0;
-}
-#endif /* CONFIG_ARCH_HAS_HUGEPD */
-
static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
mm-hmm-process-pud-swap-entry-without-pud_huge.patch
mm-gup-cache-p4d-in-follow_p4d_mask.patch
mm-gup-check-p4d-presence-before-going-on.patch
mm-x86-change-pxd_huge-behavior-to-exclude-swap-entries.patch
mm-sparc-change-pxd_huge-behavior-to-exclude-swap-entries.patch
mm-arm-use-macros-to-define-pmd-pud-helpers.patch
mm-arm-redefine-pmd_huge-with-pmd_leaf.patch
mm-arm64-merge-pxd_huge-and-pxd_leaf-definitions.patch
mm-powerpc-redefine-pxd_huge-with-pxd_leaf.patch
mm-gup-merge-pxd-huge-mapping-checks.patch
mm-treewide-replace-pxd_huge-with-pxd_leaf.patch
mm-treewide-remove-pxd_huge.patch
mm-arm-remove-pmd_thp_or_huge.patch
mm-document-pxd_leaf-api.patch
selftests-mm-run_vmtestssh-fix-hugetlb-mem-size-calculation.patch
mm-kconfig-config_pgtable_has_huge_leaves.patch
mm-hugetlb-declare-hugetlbfs_pagecache_present-non-static.patch
mm-make-hpage_pxd_-macros-even-if-thp.patch
mm-introduce-vma_pgtable_walk_beginend.patch
mm-arch-provide-pud_pfn-fallback.patch
mm-gup-drop-folio_fast_pin_allowed-in-hugepd-processing.patch
mm-gup-refactor-record_subpages-to-find-1st-small-page.patch
mm-gup-handle-hugetlb-for-no_page_table.patch
mm-gup-cache-pudp-in-follow_pud_mask.patch
mm-gup-handle-huge-pud-for-follow_pud_mask.patch
mm-gup-handle-huge-pmd-for-follow_pmd_mask.patch
mm-gup-handle-hugepd-for-follow_page.patch
mm-gup-handle-hugetlb-in-the-generic-follow_page_mask-code.patch
