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[85.23.51.1]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-59e5f568737sm188515e87.21.2026.02.11.00.13.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Feb 2026 00:13:37 -0800 (PST) From: mpenttil@redhat.com To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, =?UTF-8?q?Mika=20Penttil=C3=A4?= , David Hildenbrand , Jason Gunthorpe , Leon Romanovsky , Alistair Popple , Balbir Singh , Zi Yan , Matthew Brost Subject: [PATCH 4/6] mm: setup device page migration in HMM pagewalk Date: Wed, 11 Feb 2026 10:12:59 +0200 Message-ID: <20260211081301.2940672-5-mpenttil@redhat.com> X-Mailer: git-send-email 2.50.0 In-Reply-To: <20260211081301.2940672-1-mpenttil@redhat.com> References: <20260211081301.2940672-1-mpenttil@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: Mika Penttil=C3=A4 Implement the needed hmm_vma_handle_migrate_prepare_pmd() and hmm_vma_handle_migrate_prepare() functions which are mostly carried over from migrate_device.c, as well as the needed split functions. Make migrate_device take use of HMM pagewalk for collecting part of migration. Cc: David Hildenbrand Cc: Jason Gunthorpe Cc: Leon Romanovsky Cc: Alistair Popple Cc: Balbir Singh Cc: Zi Yan Cc: Matthew Brost Suggested-by: Alistair Popple Signed-off-by: Mika Penttil=C3=A4 --- include/linux/migrate.h | 10 +- mm/hmm.c | 403 +++++++++++++++++++++++++++++++++++++++- mm/migrate_device.c | 25 ++- 3 files changed, 425 insertions(+), 13 deletions(-) diff --git a/include/linux/migrate.h b/include/linux/migrate.h index 818272b2a7b5..104eda2dd881 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -156,6 +156,7 @@ enum migrate_vma_info { MIGRATE_VMA_SELECT_DEVICE_PRIVATE =3D 1 << 1, MIGRATE_VMA_SELECT_DEVICE_COHERENT =3D 1 << 2, MIGRATE_VMA_SELECT_COMPOUND =3D 1 << 3, + MIGRATE_VMA_FAULT =3D 1 << 4, }; =20 struct migrate_vma { @@ -193,10 +194,15 @@ struct migrate_vma { struct page *fault_page; }; =20 -// TODO: enable migration static inline enum migrate_vma_info hmm_select_migrate(struct hmm_range *r= ange) { - return 0; + enum migrate_vma_info minfo; + + minfo =3D range->migrate ? range->migrate->flags : 0; + minfo |=3D (range->default_flags & HMM_PFN_REQ_MIGRATE) ? + MIGRATE_VMA_SELECT_SYSTEM : 0; + + return minfo; } =20 int migrate_vma_setup(struct migrate_vma *args); diff --git a/mm/hmm.c b/mm/hmm.c index 22ca89b0a89e..414eed901b82 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -470,34 +470,423 @@ static int hmm_vma_handle_absent_pmd(struct mm_walk = *walk, unsigned long start, #endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ =20 #ifdef CONFIG_DEVICE_MIGRATION +/** + * migrate_vma_split_folio() - Helper function to split a THP folio + * @folio: the folio to split + * @fault_page: struct page associated with the fault if any + * + * Returns 0 on success + */ +static int migrate_vma_split_folio(struct folio *folio, + struct page *fault_page) +{ + int ret; + struct folio *fault_folio =3D fault_page ? page_folio(fault_page) : NULL; + struct folio *new_fault_folio =3D NULL; + + if (folio !=3D fault_folio) { + folio_get(folio); + folio_lock(folio); + } + + ret =3D split_folio(folio); + if (ret) { + if (folio !=3D fault_folio) { + folio_unlock(folio); + folio_put(folio); + } + return ret; + } + + new_fault_folio =3D fault_page ? page_folio(fault_page) : NULL; + + /* + * Ensure the lock is held on the correct + * folio after the split + */ + if (!new_fault_folio) { + folio_unlock(folio); + folio_put(folio); + } else if (folio !=3D new_fault_folio) { + if (new_fault_folio !=3D fault_folio) { + folio_get(new_fault_folio); + folio_lock(new_fault_folio); + } + folio_unlock(folio); + folio_put(folio); + } + + return 0; +} + static int hmm_vma_handle_migrate_prepare_pmd(const struct mm_walk *walk, pmd_t *pmdp, unsigned long start, unsigned long end, unsigned long *hmm_pfn) { - // TODO: implement migration entry insertion - return 0; + struct hmm_vma_walk *hmm_vma_walk =3D walk->private; + struct hmm_range *range =3D hmm_vma_walk->range; + struct migrate_vma *migrate =3D range->migrate; + struct folio *fault_folio =3D NULL; + struct folio *folio; + enum migrate_vma_info minfo; + unsigned long i; + int r =3D 0; + + minfo =3D hmm_select_migrate(range); + if (!minfo) + return r; + + WARN_ON_ONCE(!migrate); + HMM_ASSERT_PMD_LOCKED(hmm_vma_walk, true); + + fault_folio =3D migrate->fault_page ? + page_folio(migrate->fault_page) : NULL; + + if (pmd_none(*pmdp)) + return hmm_pfns_fill(start, end, hmm_vma_walk, 0); + + if (!(hmm_pfn[0] & HMM_PFN_VALID)) + goto out; + + if (pmd_trans_huge(*pmdp)) { + if (!(minfo & MIGRATE_VMA_SELECT_SYSTEM)) + goto out; + + folio =3D pmd_folio(*pmdp); + if (is_huge_zero_folio(folio)) + return hmm_pfns_fill(start, end, hmm_vma_walk, 0); + + } else if (!pmd_present(*pmdp)) { + const softleaf_t entry =3D softleaf_from_pmd(*pmdp); + + folio =3D softleaf_to_folio(entry); + + if (!softleaf_is_device_private(entry)) + goto out; + + if (!(minfo & MIGRATE_VMA_SELECT_DEVICE_PRIVATE)) + goto out; + + if (folio->pgmap->owner !=3D migrate->pgmap_owner) + goto out; + + } else { + hmm_vma_walk->last =3D start; + return -EBUSY; + } + + folio_get(folio); + + if (folio !=3D fault_folio && unlikely(!folio_trylock(folio))) { + folio_put(folio); + hmm_pfns_fill(start, end, hmm_vma_walk, HMM_PFN_ERROR); + return 0; + } + + if (thp_migration_supported() && + (migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) && + (IS_ALIGNED(start, HPAGE_PMD_SIZE) && + IS_ALIGNED(end, HPAGE_PMD_SIZE))) { + + struct page_vma_mapped_walk pvmw =3D { + .ptl =3D hmm_vma_walk->ptl, + .address =3D start, + .pmd =3D pmdp, + .vma =3D walk->vma, + }; + + hmm_pfn[0] |=3D HMM_PFN_MIGRATE | HMM_PFN_COMPOUND; + + r =3D set_pmd_migration_entry(&pvmw, folio_page(folio, 0)); + if (r) { + hmm_pfn[0] &=3D ~(HMM_PFN_MIGRATE | HMM_PFN_COMPOUND); + r =3D -ENOENT; // fallback + goto unlock_out; + } + for (i =3D 1, start +=3D PAGE_SIZE; start < end; start +=3D PAGE_SIZE, i= ++) + hmm_pfn[i] &=3D HMM_PFN_INOUT_FLAGS; + + } else { + r =3D -ENOENT; // fallback + goto unlock_out; + } + + +out: + return r; + +unlock_out: + if (folio !=3D fault_folio) + folio_unlock(folio); + folio_put(folio); + goto out; } =20 +/* + * Install migration entries if migration requested, either from fault + * or migrate paths. + * + */ static int hmm_vma_handle_migrate_prepare(const struct mm_walk *walk, pmd_t *pmdp, - pte_t *pte, + pte_t *ptep, unsigned long addr, unsigned long *hmm_pfn) { - // TODO: implement migration entry insertion + struct hmm_vma_walk *hmm_vma_walk =3D walk->private; + struct hmm_range *range =3D hmm_vma_walk->range; + struct migrate_vma *migrate =3D range->migrate; + struct mm_struct *mm =3D walk->vma->vm_mm; + struct folio *fault_folio =3D NULL; + enum migrate_vma_info minfo; + struct dev_pagemap *pgmap; + bool anon_exclusive; + struct folio *folio; + unsigned long pfn; + struct page *page; + softleaf_t entry; + pte_t pte, swp_pte; + bool writable =3D false; + + // Do we want to migrate at all? + minfo =3D hmm_select_migrate(range); + if (!minfo) + return 0; + + WARN_ON_ONCE(!migrate); + HMM_ASSERT_PTE_LOCKED(hmm_vma_walk, true); + + fault_folio =3D migrate->fault_page ? + page_folio(migrate->fault_page) : NULL; + + pte =3D ptep_get(ptep); + + if (pte_none(pte)) { + // migrate without faulting case + if (vma_is_anonymous(walk->vma)) { + *hmm_pfn &=3D HMM_PFN_INOUT_FLAGS; + *hmm_pfn |=3D HMM_PFN_MIGRATE | HMM_PFN_VALID; + goto out; + } + } + + if (!(hmm_pfn[0] & HMM_PFN_VALID)) + goto out; + + if (!pte_present(pte)) { + /* + * Only care about unaddressable device page special + * page table entry. Other special swap entries are not + * migratable, and we ignore regular swapped page. + */ + entry =3D softleaf_from_pte(pte); + if (!softleaf_is_device_private(entry)) + goto out; + + if (!(minfo & MIGRATE_VMA_SELECT_DEVICE_PRIVATE)) + goto out; + + page =3D softleaf_to_page(entry); + folio =3D page_folio(page); + if (folio->pgmap->owner !=3D migrate->pgmap_owner) + goto out; + + if (folio_test_large(folio)) { + int ret; + + pte_unmap_unlock(ptep, hmm_vma_walk->ptl); + hmm_vma_walk->ptelocked =3D false; + ret =3D migrate_vma_split_folio(folio, + migrate->fault_page); + if (ret) + goto out_error; + return -EAGAIN; + } + + pfn =3D page_to_pfn(page); + if (softleaf_is_device_private_write(entry)) + writable =3D true; + } else { + pfn =3D pte_pfn(pte); + if (is_zero_pfn(pfn) && + (minfo & MIGRATE_VMA_SELECT_SYSTEM)) { + *hmm_pfn =3D HMM_PFN_MIGRATE|HMM_PFN_VALID; + goto out; + } + page =3D vm_normal_page(walk->vma, addr, pte); + if (page && !is_zone_device_page(page) && + !(minfo & MIGRATE_VMA_SELECT_SYSTEM)) { + goto out; + } else if (page && is_device_coherent_page(page)) { + pgmap =3D page_pgmap(page); + + if (!(minfo & + MIGRATE_VMA_SELECT_DEVICE_COHERENT) || + pgmap->owner !=3D migrate->pgmap_owner) + goto out; + } + + folio =3D page ? page_folio(page) : NULL; + if (folio && folio_test_large(folio)) { + int ret; + + pte_unmap_unlock(ptep, hmm_vma_walk->ptl); + hmm_vma_walk->ptelocked =3D false; + + ret =3D migrate_vma_split_folio(folio, + migrate->fault_page); + if (ret) + goto out_error; + return -EAGAIN; + } + + writable =3D pte_write(pte); + } + + if (!page || !page->mapping) + goto out; + + /* + * By getting a reference on the folio we pin it and that blocks + * any kind of migration. Side effect is that it "freezes" the + * pte. + * + * We drop this reference after isolating the folio from the lru + * for non device folio (device folio are not on the lru and thus + * can't be dropped from it). + */ + folio =3D page_folio(page); + folio_get(folio); + + /* + * We rely on folio_trylock() to avoid deadlock between + * concurrent migrations where each is waiting on the others + * folio lock. If we can't immediately lock the folio we fail this + * migration as it is only best effort anyway. + * + * If we can lock the folio it's safe to set up a migration entry + * now. In the common case where the folio is mapped once in a + * single process setting up the migration entry now is an + * optimisation to avoid walking the rmap later with + * try_to_migrate(). + */ + + if (fault_folio =3D=3D folio || folio_trylock(folio)) { + anon_exclusive =3D folio_test_anon(folio) && + PageAnonExclusive(page); + + flush_cache_page(walk->vma, addr, pfn); + + if (anon_exclusive) { + pte =3D ptep_clear_flush(walk->vma, addr, ptep); + + if (folio_try_share_anon_rmap_pte(folio, page)) { + set_pte_at(mm, addr, ptep, pte); + folio_unlock(folio); + folio_put(folio); + goto out; + } + } else { + pte =3D ptep_get_and_clear(mm, addr, ptep); + } + + if (pte_dirty(pte)) + folio_mark_dirty(folio); + + /* Setup special migration page table entry */ + if (writable) + entry =3D make_writable_migration_entry(pfn); + else if (anon_exclusive) + entry =3D make_readable_exclusive_migration_entry(pfn); + else + entry =3D make_readable_migration_entry(pfn); + + if (pte_present(pte)) { + if (pte_young(pte)) + entry =3D make_migration_entry_young(entry); + if (pte_dirty(pte)) + entry =3D make_migration_entry_dirty(entry); + } + + swp_pte =3D swp_entry_to_pte(entry); + if (pte_present(pte)) { + if (pte_soft_dirty(pte)) + swp_pte =3D pte_swp_mksoft_dirty(swp_pte); + if (pte_uffd_wp(pte)) + swp_pte =3D pte_swp_mkuffd_wp(swp_pte); + } else { + if (pte_swp_soft_dirty(pte)) + swp_pte =3D pte_swp_mksoft_dirty(swp_pte); + if (pte_swp_uffd_wp(pte)) + swp_pte =3D pte_swp_mkuffd_wp(swp_pte); + } + + set_pte_at(mm, addr, ptep, swp_pte); + folio_remove_rmap_pte(folio, page, walk->vma); + folio_put(folio); + *hmm_pfn |=3D HMM_PFN_MIGRATE; + + if (pte_present(pte)) + flush_tlb_range(walk->vma, addr, addr + PAGE_SIZE); + } else + folio_put(folio); +out: return 0; +out_error: + return -EFAULT; } =20 static int hmm_vma_walk_split(pmd_t *pmdp, unsigned long addr, struct mm_walk *walk) { - // TODO : implement split - return 0; -} + struct hmm_vma_walk *hmm_vma_walk =3D walk->private; + struct hmm_range *range =3D hmm_vma_walk->range; + struct migrate_vma *migrate =3D range->migrate; + struct folio *folio, *fault_folio; + spinlock_t *ptl; + int ret =3D 0; + + HMM_ASSERT_UNLOCKED(hmm_vma_walk); =20 + fault_folio =3D (migrate && migrate->fault_page) ? + page_folio(migrate->fault_page) : NULL; + + ptl =3D pmd_lock(walk->mm, pmdp); + if (unlikely(!pmd_trans_huge(*pmdp))) { + spin_unlock(ptl); + goto out; + } + + folio =3D pmd_folio(*pmdp); + if (is_huge_zero_folio(folio)) { + spin_unlock(ptl); + split_huge_pmd(walk->vma, pmdp, addr); + } else { + folio_get(folio); + spin_unlock(ptl); + + if (folio !=3D fault_folio) { + if (unlikely(!folio_trylock(folio))) { + folio_put(folio); + ret =3D -EBUSY; + goto out; + } + } else + folio_put(folio); + + ret =3D split_folio(folio); + if (fault_folio !=3D folio) { + folio_unlock(folio); + folio_put(folio); + } + + } +out: + return ret; +} #else static int hmm_vma_handle_migrate_prepare_pmd(const struct mm_walk *walk, pmd_t *pmdp, diff --git a/mm/migrate_device.c b/mm/migrate_device.c index c773a82ea1ed..222cce2e934d 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -734,7 +734,16 @@ static void migrate_vma_unmap(struct migrate_vma *migr= ate) */ int migrate_vma_setup(struct migrate_vma *args) { + int ret; long nr_pages =3D (args->end - args->start) >> PAGE_SHIFT; + struct hmm_range range =3D { + .notifier =3D NULL, + .start =3D args->start, + .end =3D args->end, + .hmm_pfns =3D args->src, + .dev_private_owner =3D args->pgmap_owner, + .migrate =3D args + }; =20 args->start &=3D PAGE_MASK; args->end &=3D PAGE_MASK; @@ -759,17 +768,25 @@ int migrate_vma_setup(struct migrate_vma *args) args->cpages =3D 0; args->npages =3D 0; =20 - migrate_vma_collect(args); + if (args->flags & MIGRATE_VMA_FAULT) + range.default_flags |=3D HMM_PFN_REQ_FAULT; + + ret =3D hmm_range_fault(&range); =20 - if (args->cpages) - migrate_vma_unmap(args); + migrate_hmm_range_setup(&range); + + /* Remove migration PTEs */ + if (ret) { + migrate_vma_pages(args); + migrate_vma_finalize(args); + } =20 /* * At this point pages are locked and unmapped, and thus they have * stable content and can safely be copied to destination memory that * is allocated by the drivers. */ - return 0; + return ret; =20 } EXPORT_SYMBOL(migrate_vma_setup); --=20 2.50.0