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[89.27.86.246]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5b8d46e0966sm191742e87.55.2026.09.21.22.34.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Sep 2026 22:34:55 -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 v14 06/12] mm/hmm: migrate collection in HMM pagewalk - pte level Date: Tue, 22 Sep 2026 08:34:15 +0300 Message-ID: <20260922053421.4092027-7-mpenttil@redhat.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260922053421.4092027-1-mpenttil@redhat.com> References: <20260922053421.4092027-1-mpenttil@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: v_p5kT3QulUd7abADhGc8C5mvld3CalhGmmm_dMuWZ0_1790055298 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: wos47u8th7o789r61qohkbqzc31u5xc4 X-Rspam-User: X-Rspamd-Queue-Id: 5DE73A0007 X-Rspamd-Server: rspam03 X-HE-Tag: 1790055301-933796 X-HE-Meta: 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 CXRL/nDc 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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 | 262 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 261 insertions(+), 1 deletion(-) diff --git a/mm/hmm.c b/mm/hmm.c index e6469ef4ae6a..b3b79d13c797 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -489,6 +489,63 @@ 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, @@ -499,6 +556,11 @@ 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, @@ -506,8 +568,206 @@ 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); + 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; } static int hmm_vma_walk_split(pmd_t *pmdp, -- 2.55.0