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[85.23.51.1]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a15602e692sm3263397e87.30.2026.03.15.23.24.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Mar 2026 23:24:34 -0700 (PDT) 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 v6 4/6] mm: setup device page migration in HMM pagewalk Date: Mon, 16 Mar 2026 08:24:05 +0200 Message-ID: <20260316062407.3354636-5-mpenttil@redhat.com> X-Mailer: git-send-email 2.50.0 In-Reply-To: <20260316062407.3354636-1-mpenttil@redhat.com> References: <20260316062407.3354636-1-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: 8bit From: Mika Penttilä 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 Penttilä --- include/linux/migrate.h | 9 +- mm/hmm.c | 420 ++++++++++++++++++++++++++++++++++++++-- mm/migrate_device.c | 26 ++- 3 files changed, 438 insertions(+), 17 deletions(-) diff --git a/include/linux/migrate.h b/include/linux/migrate.h index 037e7430edb9..9e1081847d1f 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -163,6 +163,7 @@ enum migrate_vma_info { MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1, MIGRATE_VMA_SELECT_DEVICE_COHERENT = 1 << 2, MIGRATE_VMA_SELECT_COMPOUND = 1 << 3, + MIGRATE_VMA_FAULT = 1 << 4, }; struct migrate_vma { @@ -200,10 +201,14 @@ struct migrate_vma { struct page *fault_page; }; -// TODO: enable migration static inline enum migrate_vma_info hmm_select_migrate(struct hmm_range *range) { - return 0; + enum migrate_vma_info minfo; + + minfo = (range->default_flags & HMM_PFN_REQ_MIGRATE) ? + range->migrate->flags : 0; + + return minfo; } int migrate_vma_setup(struct migrate_vma *args); diff --git a/mm/hmm.c b/mm/hmm.c index c302de5b67d9..69d88fe16882 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -470,34 +470,424 @@ static int hmm_vma_handle_absent_pmd(struct mm_walk *walk, unsigned long start, #endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ #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 = fault_page ? page_folio(fault_page) : NULL; + struct folio *new_fault_folio = NULL; + + if (folio != fault_folio) { + folio_get(folio); + folio_lock(folio); + } + + ret = split_folio(folio); + if (ret) { + if (folio != fault_folio) { + folio_unlock(folio); + folio_put(folio); + } + return ret; + } + + new_fault_folio = 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 != new_fault_folio) { + if (new_fault_folio != 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 = walk->private; + struct hmm_range *range = hmm_vma_walk->range; + struct migrate_vma *migrate = range->migrate; + struct folio *fault_folio = NULL; + struct folio *folio; + enum migrate_vma_info minfo; + unsigned long i; + int r = 0; + + minfo = hmm_select_migrate(range); + if (!minfo) + return r; + + WARN_ON_ONCE(!migrate); + HMM_ASSERT_PMD_LOCKED(hmm_vma_walk, true); + + fault_folio = 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 = 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 = softleaf_from_pmd(*pmdp); + + folio = 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 != migrate->pgmap_owner) + goto out; + + } else { + hmm_vma_walk->last = start; + return -EBUSY; + } + + folio_get(folio); + + if (folio != 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 = { + .ptl = hmm_vma_walk->ptl, + .address = start, + .pmd = pmdp, + .vma = walk->vma, + }; + + hmm_pfn[0] |= HMM_PFN_MIGRATE | HMM_PFN_COMPOUND; + + r = set_pmd_migration_entry(&pvmw, folio_page(folio, 0)); + if (r) { + hmm_pfn[0] &= ~(HMM_PFN_MIGRATE | HMM_PFN_COMPOUND); + r = -ENOENT; // fallback + goto unlock_out; + } + for (i = 1, start += PAGE_SIZE; start < end; start += PAGE_SIZE, i++) + hmm_pfn[i] &= HMM_PFN_INOUT_FLAGS; + + } else { + r = -ENOENT; // fallback + goto unlock_out; + } + + +out: + return r; + +unlock_out: + if (folio != fault_folio) + folio_unlock(folio); + folio_put(folio); + goto out; } +/* + * 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) + unsigned long *hmm_pfn, + bool *unmapped) { - // TODO: implement migration entry insertion + struct hmm_vma_walk *hmm_vma_walk = walk->private; + struct hmm_range *range = hmm_vma_walk->range; + struct migrate_vma *migrate = range->migrate; + struct mm_struct *mm = walk->vma->vm_mm; + struct folio *fault_folio = 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 = false; + + // Do we want to migrate at all? + minfo = hmm_select_migrate(range); + if (!minfo) + return 0; + + WARN_ON_ONCE(!migrate); + HMM_ASSERT_PTE_LOCKED(hmm_vma_walk, true); + + fault_folio = migrate->fault_page ? + page_folio(migrate->fault_page) : NULL; + + pte = ptep_get(ptep); + + if (pte_none(pte)) { + // migrate without faulting case + if (vma_is_anonymous(walk->vma)) { + *hmm_pfn &= HMM_PFN_INOUT_FLAGS; + *hmm_pfn |= 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 = softleaf_from_pte(pte); + if (!softleaf_is_device_private(entry)) + goto out; + + if (!(minfo & MIGRATE_VMA_SELECT_DEVICE_PRIVATE)) + goto out; + + page = softleaf_to_page(entry); + folio = page_folio(page); + if (folio->pgmap->owner != migrate->pgmap_owner) + goto out; + + if (folio_test_large(folio)) { + int ret; + + pte_unmap_unlock(ptep, hmm_vma_walk->ptl); + hmm_vma_walk->ptelocked = false; + ret = migrate_vma_split_folio(folio, + migrate->fault_page); + if (ret) + goto out_error; + return -EAGAIN; + } + + pfn = page_to_pfn(page); + if (softleaf_is_device_private_write(entry)) + writable = true; + } else { + pfn = pte_pfn(pte); + if (is_zero_pfn(pfn) && + (minfo & MIGRATE_VMA_SELECT_SYSTEM)) { + *hmm_pfn = HMM_PFN_MIGRATE|HMM_PFN_VALID; + goto out; + } + page = 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 = page_pgmap(page); + + if (!(minfo & + MIGRATE_VMA_SELECT_DEVICE_COHERENT) || + pgmap->owner != migrate->pgmap_owner) + goto out; + } + + folio = 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 = false; + + ret = migrate_vma_split_folio(folio, + migrate->fault_page); + if (ret) + goto out_error; + return -EAGAIN; + } + + writable = 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 = 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 == folio || folio_trylock(folio)) { + anon_exclusive = folio_test_anon(folio) && + PageAnonExclusive(page); + + flush_cache_page(walk->vma, addr, pfn); + + if (anon_exclusive) { + pte = 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 = ptep_get_and_clear(mm, addr, ptep); + } + + if (pte_dirty(pte)) + folio_mark_dirty(folio); + + /* Setup special migration page table entry */ + if (writable) + entry = make_writable_migration_entry(pfn); + else if (anon_exclusive) + entry = make_readable_exclusive_migration_entry(pfn); + else + entry = make_readable_migration_entry(pfn); + + if (pte_present(pte)) { + if (pte_young(pte)) + entry = make_migration_entry_young(entry); + if (pte_dirty(pte)) + entry = make_migration_entry_dirty(entry); + } + + swp_pte = swp_entry_to_pte(entry); + if (pte_present(pte)) { + if (pte_soft_dirty(pte)) + swp_pte = pte_swp_mksoft_dirty(swp_pte); + if (pte_uffd_wp(pte)) + swp_pte = pte_swp_mkuffd_wp(swp_pte); + } else { + if (pte_swp_soft_dirty(pte)) + swp_pte = pte_swp_mksoft_dirty(swp_pte); + if (pte_swp_uffd_wp(pte)) + swp_pte = 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 |= HMM_PFN_MIGRATE; + + if (pte_present(pte)) + *unmapped = true; + } else + folio_put(folio); +out: return 0; +out_error: + return -EFAULT; } 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 = walk->private; + struct hmm_range *range = hmm_vma_walk->range; + struct migrate_vma *migrate = range->migrate; + struct folio *folio, *fault_folio; + spinlock_t *ptl; + int ret = 0; + HMM_ASSERT_UNLOCKED(hmm_vma_walk); + + fault_folio = (migrate && migrate->fault_page) ? + page_folio(migrate->fault_page) : NULL; + + ptl = pmd_lock(walk->mm, pmdp); + if (unlikely(!pmd_trans_huge(*pmdp))) { + spin_unlock(ptl); + goto out; + } + + folio = 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 != fault_folio) { + if (unlikely(!folio_trylock(folio))) { + folio_put(folio); + ret = -EBUSY; + goto out; + } + } else + folio_put(folio); + + ret = split_folio(folio); + if (fault_folio != 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, @@ -512,7 +902,8 @@ static int hmm_vma_handle_migrate_prepare(const struct mm_walk *walk, pmd_t *pmdp, pte_t *pte, unsigned long addr, - unsigned long *hmm_pfn) + unsigned long *hmm_pfn, + bool *unmapped) { return 0; } @@ -567,6 +958,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, enum migrate_vma_info minfo; unsigned long addr = start; unsigned long *hmm_pfns; + bool unmapped = false; unsigned long i; pte_t *ptep; pmd_t pmd; @@ -648,7 +1040,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, goto again; } - r = hmm_vma_handle_pmd(walk, addr, end, hmm_pfns, pmd); + r = hmm_vma_handle_pmd(walk, start, end, hmm_pfns, pmd); // If not migrating we are done if (r || !minfo) { @@ -717,9 +1109,13 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, return r; } - r = hmm_vma_handle_migrate_prepare(walk, pmdp, ptep, addr, hmm_pfns); + r = hmm_vma_handle_migrate_prepare(walk, pmdp, ptep, addr, hmm_pfns, &unmapped); if (r == -EAGAIN) { HMM_ASSERT_UNLOCKED(hmm_vma_walk); + if (unmapped) { + flush_tlb_range(walk->vma, start, addr); + unmapped = false; + } goto again; } if (r) { @@ -727,6 +1123,8 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, break; } } + if (unmapped) + flush_tlb_range(walk->vma, start, addr); if (hmm_vma_walk->ptelocked) { pte_unmap_unlock(ptep - 1, hmm_vma_walk->ptl); diff --git a/mm/migrate_device.c b/mm/migrate_device.c index b320ea3736b4..cef9b644d31f 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -734,7 +734,17 @@ static void migrate_vma_unmap(struct migrate_vma *migrate) */ int migrate_vma_setup(struct migrate_vma *args) { + int ret; long nr_pages = (args->end - args->start) >> PAGE_SHIFT; + struct hmm_range range = { + .notifier = NULL, + .start = args->start, + .end = args->end, + .hmm_pfns = args->src, + .dev_private_owner = args->pgmap_owner, + .migrate = args, + .default_flags = HMM_PFN_REQ_MIGRATE + }; args->start &= PAGE_MASK; args->end &= PAGE_MASK; @@ -759,17 +769,25 @@ int migrate_vma_setup(struct migrate_vma *args) args->cpages = 0; args->npages = 0; - migrate_vma_collect(args); + if (args->flags & MIGRATE_VMA_FAULT) + range.default_flags |= HMM_PFN_REQ_FAULT; + + ret = hmm_range_fault(&range); - 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); + } /* * 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; } EXPORT_SYMBOL(migrate_vma_setup); -- 2.50.0