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[89.27.86.246]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-3a63bf57909sm4803141fa.29.2026.09.23.23.53.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2026 23:53:47 -0700 (PDT) From: mpenttil@redhat.com To: linux-mm@kvack.org Cc: dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, 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 , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko Subject: [PATCH v15 05/11] mm/hmm: migrate collection in HMM pagewalk - pte level Date: Thu, 24 Sep 2026 09:53:07 +0300 Message-ID: <20260924065313.899730-6-mpenttil@redhat.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260924065313.899730-1-mpenttil@redhat.com> References: <20260924065313.899730-1-mpenttil@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: FXJzKVnUIqymJ_8ihdlJE-QnQN4a9NL7H563Xx9LTaI_1790232829 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 5FA7C80002 X-Stat-Signature: 5wng3tyggxjf9ctf7ca3wu8rbr6bj6on X-Rspam-User: X-HE-Tag: 1790232832-377905 X-HE-Meta: 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 sVKO629H 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Mika Penttilä Implement the needed hmm_vma_handle_migrate_prepare() function which is mostly carried over from migrate_device.c's migrate_vma_collect_pmd() function. Also implement the migrate_vma_split_folio(), for splitting pte mapped large folios. It is also mostly from migrate_device.c, with care taken to reference folio before relasing page table lock. With HMM pagewalk based migration, the idea is that hmm_vma_handle_*() are responsible for faulting, and the pfn collecting part. hmm_vma_handle_migrate_prepare*() do the migration decisions (with HMM_PFN_MIGRATE), possibly split folios, and insert migration ptes/pmds. HMM pagewalk based migration is enabled in later commit, for now now hmm_select_migrate() returns 0. 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 --- mm/hmm.c | 263 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 262 insertions(+), 1 deletion(-) diff --git a/mm/hmm.c b/mm/hmm.c index 25f537c87b5f..a60b66963049 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -491,6 +491,63 @@ static int hmm_vma_handle_absent_pmd(struct mm_walk *walk, unsigned long start, #endif /* CONFIG_ARCH_HAS_PMD_SOFTLEAVES */ #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 + * @hmm_vma_walk: walk in progress + * @ptep: pte_t * for unmap and unlock ptl + * + * Returns 0 on success + */ +static int migrate_vma_split_folio(struct folio *folio, + struct page *fault_page, + struct hmm_vma_walk *hmm_vma_walk, + pte_t *ptep) +{ + 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); + + pte_unmap_unlock(ptep, hmm_vma_walk->ptl); + hmm_vma_walk->ptelocked = false; + + if (folio != fault_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, @@ -501,6 +558,11 @@ static int hmm_vma_handle_migrate_prepare_pmd(const struct mm_walk *walk, return 0; } +/* + * 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 *ptep, @@ -508,8 +570,207 @@ static int hmm_vma_handle_migrate_prepare(const struct mm_walk *walk, 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)) { + if (vma_is_anonymous(walk->vma)) { + *hmm_pfn &= HMM_PFN_INOUT_FLAGS; + *hmm_pfn |= HMM_PFN_MIGRATE; + 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; + + ret = migrate_vma_split_folio(folio, + migrate->fault_page, + hmm_vma_walk, + ptep); + 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; + 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; + + ret = migrate_vma_split_folio(folio, + migrate->fault_page, + hmm_vma_walk, + ptep); + 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); + + if (pte_present(pte)) + 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); + if (fault_folio != folio) + folio_unlock(folio); + folio_put(folio); + goto out; + } + } else { + pte = ptep_get_and_clear(mm, addr, ptep); + } + + if (pte_present(pte) && 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(pte)) + swp_pte = pte_swp_mkuffd(swp_pte); + } else { + if (pte_swp_soft_dirty(pte)) + swp_pte = pte_swp_mksoft_dirty(swp_pte); + if (pte_swp_uffd(pte)) + swp_pte = pte_swp_mkuffd(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; } #else -- 2.55.0