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[85.23.48.6]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-3340a473b7fsm29096571fa.27.2025.08.20.22.10.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Aug 2025 22:10:32 -0700 (PDT) Message-ID: <953cb2f5-a27f-4eac-b2b8-ee67e35bd1e4@redhat.com> Date: Thu, 21 Aug 2025 08:10:31 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/4] mm: unified fault and migrate device page paths To: Balbir Singh , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, David Hildenbrand , Jason Gunthorpe , Leon Romanovsky , Alistair Popple References: <20250814072045.3637192-1-mpenttil@redhat.com> <20250814072045.3637192-4-mpenttil@redhat.com> <099ffad3-489b-4325-b5dc-90fa002132f7@nvidia.com> Content-Language: en-US From: =?UTF-8?Q?Mika_Penttil=C3=A4?= In-Reply-To: <099ffad3-489b-4325-b5dc-90fa002132f7@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/21/25 07:30, Balbir Singh wrote: > On 8/14/25 17:19, Mika Penttilä wrote: >> As of this writing, the way device page faulting and migration works >> is not optimal, if you want to do both fault handling and >> migration at once. >> >> Being able to migrate not present pages (or pages mapped with incorrect >> permissions, eg. COW) to the GPU requires doing either of the >> following sequences: >> >> 1. hmm_range_fault() - fault in non-present pages with correct permissions, etc. >> 2. migrate_vma_*() - migrate the pages >> >> Or: >> >> 1. migrate_vma_*() - migrate present pages >> 2. If non-present pages detected by migrate_vma_*(): >> a) call hmm_range_fault() to fault pages in >> b) call migrate_vma_*() again to migrate now present pages >> >> The problem with the first sequence is that you always have to do two >> page walks even when most of the time the pages are present or zero page >> mappings so the common case takes a performance hit. >> >> The second sequence is better for the common case, but far worse if >> pages aren't present because now you have to walk the page tables three >> times (once to find the page is not present, once so hmm_range_fault() >> can find a non-present page to fault in and once again to setup the >> migration). It also tricky to code correctly. >> >> We should be able to walk the page table once, faulting >> pages in as required and replacing them with migration entries if >> requested. >> >> Add a new flag to HMM APIs, HMM_PFN_REQ_MIGRATE, >> which tells to prepare for migration also during fault handling. >> Also, for the migrate_vma_setup() call paths, a flags, MIGRATE_VMA_FAULT, >> is added to tell to add fault handling to migrate. >> >> Cc: David Hildenbrand >> Cc: Jason Gunthorpe >> Cc: Leon Romanovsky >> Cc: Alistair Popple >> Cc: Balbir Singh >> >> Suggested-by: Alistair Popple >> Signed-off-by: Mika Penttilä >> --- >> include/linux/hmm.h | 10 +- >> include/linux/migrate.h | 6 +- >> mm/hmm.c | 351 ++++++++++++++++++++++++++++++++++++++-- >> mm/migrate_device.c | 72 ++++++++- >> 4 files changed, 420 insertions(+), 19 deletions(-) >> >> diff --git a/include/linux/hmm.h b/include/linux/hmm.h >> index db75ffc949a7..7485e549c675 100644 >> --- a/include/linux/hmm.h >> +++ b/include/linux/hmm.h >> @@ -12,7 +12,7 @@ >> #include >> >> struct mmu_interval_notifier; >> - >> +struct migrate_vma; >> /* >> * On output: >> * 0 - The page is faultable and a future call with >> @@ -48,11 +48,14 @@ enum hmm_pfn_flags { >> HMM_PFN_P2PDMA = 1UL << (BITS_PER_LONG - 5), >> HMM_PFN_P2PDMA_BUS = 1UL << (BITS_PER_LONG - 6), >> >> - HMM_PFN_ORDER_SHIFT = (BITS_PER_LONG - 11), >> + /* Migrate request */ >> + HMM_PFN_MIGRATE = 1UL << (BITS_PER_LONG - 7), >> + HMM_PFN_ORDER_SHIFT = (BITS_PER_LONG - 12), >> >> /* Input flags */ >> HMM_PFN_REQ_FAULT = HMM_PFN_VALID, >> HMM_PFN_REQ_WRITE = HMM_PFN_WRITE, >> + HMM_PFN_REQ_MIGRATE = HMM_PFN_MIGRATE, >> >> HMM_PFN_FLAGS = ~((1UL << HMM_PFN_ORDER_SHIFT) - 1), >> }; >> @@ -107,6 +110,7 @@ static inline unsigned int hmm_pfn_to_map_order(unsigned long hmm_pfn) >> * @default_flags: default flags for the range (write, read, ... see hmm doc) >> * @pfn_flags_mask: allows to mask pfn flags so that only default_flags matter >> * @dev_private_owner: owner of device private pages >> + * @migrate: structure for migrating the associated vma >> */ >> struct hmm_range { >> struct mmu_interval_notifier *notifier; >> @@ -117,12 +121,14 @@ struct hmm_range { >> unsigned long default_flags; >> unsigned long pfn_flags_mask; >> void *dev_private_owner; >> + struct migrate_vma *migrate; >> }; >> >> /* >> * Please see Documentation/mm/hmm.rst for how to use the range API. >> */ >> int hmm_range_fault(struct hmm_range *range); >> +int hmm_range_migrate_prepare(struct hmm_range *range, struct migrate_vma **pargs); >> >> /* >> * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range >> diff --git a/include/linux/migrate.h b/include/linux/migrate.h >> index acadd41e0b5c..ab35d0f1f65d 100644 >> --- a/include/linux/migrate.h >> +++ b/include/linux/migrate.h >> @@ -3,6 +3,7 @@ >> #define _LINUX_MIGRATE_H >> >> #include >> +#include >> #include >> #include >> #include >> @@ -143,10 +144,11 @@ static inline unsigned long migrate_pfn(unsigned long pfn) >> return (pfn << MIGRATE_PFN_SHIFT) | MIGRATE_PFN_VALID; >> } >> >> -enum migrate_vma_direction { >> +enum migrate_vma_info { >> MIGRATE_VMA_SELECT_SYSTEM = 1 << 0, >> MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1, >> MIGRATE_VMA_SELECT_DEVICE_COHERENT = 1 << 2, >> + MIGRATE_VMA_FAULT = 1 << 3, >> }; >> > I suspect there are some points of conflict with my series that can be resolved Yes there are some, I have also been looking into them and seem not too bad. > >> struct migrate_vma { >> @@ -194,7 +196,7 @@ void migrate_device_pages(unsigned long *src_pfns, unsigned long *dst_pfns, >> unsigned long npages); >> void migrate_device_finalize(unsigned long *src_pfns, >> unsigned long *dst_pfns, unsigned long npages); >> - >> +void migrate_hmm_range_setup(struct hmm_range *range); >> #endif /* CONFIG_MIGRATION */ >> >> #endif /* _LINUX_MIGRATE_H */ >> diff --git a/mm/hmm.c b/mm/hmm.c >> index d545e2494994..8cb2b325fa9f 100644 >> --- a/mm/hmm.c >> +++ b/mm/hmm.c >> @@ -20,6 +20,7 @@ >> #include >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -33,6 +34,10 @@ >> struct hmm_vma_walk { >> struct hmm_range *range; >> unsigned long last; >> + struct mmu_notifier_range mmu_range; >> + struct vm_area_struct *vma; >> + unsigned long start; >> + unsigned long end; >> }; >> >> enum { >> @@ -47,15 +52,33 @@ enum { >> HMM_PFN_P2PDMA_BUS, >> }; >> >> +static enum migrate_vma_info hmm_want_migrate(struct hmm_range *range) > hmm_want_migrate -> hmm_select_and_migrate? Yeah maybe that's better > >> +{ >> + enum migrate_vma_info minfo; >> + >> + minfo = range->migrate ? range->migrate->flags : 0; >> + minfo |= (range->default_flags & HMM_PFN_REQ_MIGRATE) ? >> + MIGRATE_VMA_SELECT_SYSTEM : 0; >> + > Just to understand, this selects just system pages Yes it indicates the migration type for the fault path (migrate on fault). > >> + return minfo; >> +} >> + >> static int hmm_pfns_fill(unsigned long addr, unsigned long end, >> - struct hmm_range *range, unsigned long cpu_flags) >> + struct hmm_vma_walk *hmm_vma_walk, unsigned long cpu_flags) >> { >> + struct hmm_range *range = hmm_vma_walk->range; >> unsigned long i = (addr - range->start) >> PAGE_SHIFT; >> >> + if (cpu_flags != HMM_PFN_ERROR) >> + if (hmm_want_migrate(range) && >> + (vma_is_anonymous(hmm_vma_walk->vma))) >> + cpu_flags |= (HMM_PFN_VALID | HMM_PFN_MIGRATE); >> + >> for (; addr < end; addr += PAGE_SIZE, i++) { >> range->hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS; >> range->hmm_pfns[i] |= cpu_flags; >> } >> + >> return 0; >> } >> >> @@ -171,11 +194,11 @@ static int hmm_vma_walk_hole(unsigned long addr, unsigned long end, >> if (!walk->vma) { >> if (required_fault) >> return -EFAULT; >> - return hmm_pfns_fill(addr, end, range, HMM_PFN_ERROR); >> + return hmm_pfns_fill(addr, end, hmm_vma_walk, HMM_PFN_ERROR); >> } >> if (required_fault) >> return hmm_vma_fault(addr, end, required_fault, walk); >> - return hmm_pfns_fill(addr, end, range, 0); >> + return hmm_pfns_fill(addr, end, hmm_vma_walk, 0); >> } >> >> static inline unsigned long hmm_pfn_flags_order(unsigned long order) >> @@ -326,6 +349,257 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, >> return hmm_vma_fault(addr, end, required_fault, walk); >> } >> >> +/* >> + * Install migration entries if migration requested, either from fault >> + * or migrate paths. >> + * >> + */ >> +static void hmm_vma_handle_migrate_prepare(const struct mm_walk *walk, >> + pmd_t *pmdp, >> + unsigned long addr, >> + unsigned long *hmm_pfn) >> +{ >> + 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; >> + swp_entry_t entry; >> + pte_t pte, swp_pte; >> + spinlock_t *ptl; >> + bool writable = false; >> + pte_t *ptep; >> + >> + >> + // Do we want to migrate at all? >> + minfo = hmm_want_migrate(range); >> + if (!minfo) >> + return; >> + >> + fault_folio = (migrate && migrate->fault_page) ? >> + page_folio(migrate->fault_page) : NULL; >> + >> + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); >> + if (!ptep) >> + return; >> + >> + pte = ptep_get(ptep); >> + >> + if (pte_none(pte)) { >> + // migrate without faulting case >> + if (vma_is_anonymous(walk->vma)) >> + *hmm_pfn = HMM_PFN_MIGRATE|HMM_PFN_VALID; >> + goto out; >> + } >> + >> + if (!(*hmm_pfn & 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 = pte_to_swp_entry(pte); >> + if (!is_device_private_entry(entry)) >> + goto out; >> + >> + // We have already checked that are the pgmap owners >> + if (!(minfo & MIGRATE_VMA_SELECT_DEVICE_PRIVATE)) >> + goto out; >> + >> + page = pfn_swap_entry_to_page(entry); >> + pfn = page_to_pfn(page); >> + if (is_writable_device_private_entry(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; >> + } >> + writable = pte_write(pte); >> + } >> + >> + /* FIXME support THP */ >> + if (!page || !page->mapping || PageTransCompound(page)) >> + 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); >> + } >> + >> + /* 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); >> + >> + 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)) >> + flush_tlb_range(walk->vma, addr, addr + PAGE_SIZE); >> + } else >> + folio_put(folio); >> +out: >> + pte_unmap_unlock(ptep, ptl); >> + >> +} >> + >> +static int hmm_vma_walk_split(pmd_t *pmdp, >> + unsigned long addr, >> + struct mm_walk *walk) >> +{ >> + 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; >> + >> + 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); >> + /* FIXME: we don't expect THP for fault_folio */ >> + if (WARN_ON_ONCE(fault_folio == folio)) { >> + folio_put(folio); >> + ret = -EBUSY; >> + goto out; >> + } >> + if (unlikely(!folio_trylock(folio))) { >> + folio_put(folio); >> + ret = -EBUSY; >> + goto out; >> + } >> + ret = split_folio(folio); >> + folio_unlock(folio); >> + folio_put(folio); >> + } >> +out: >> + return ret; >> +} >> + >> +static int hmm_vma_capture_migrate_range(unsigned long start, >> + unsigned long end, >> + struct mm_walk *walk) >> +{ >> + struct hmm_vma_walk *hmm_vma_walk = walk->private; >> + struct hmm_range *range = hmm_vma_walk->range; >> + >> + if (!hmm_want_migrate(range)) >> + return 0; >> + >> + if (hmm_vma_walk->vma && (hmm_vma_walk->vma != walk->vma)) >> + return -ERANGE; >> + >> + hmm_vma_walk->vma = walk->vma; >> + hmm_vma_walk->start = start; >> + hmm_vma_walk->end = end; >> + >> + if (end - start > range->end - range->start) >> + return -ERANGE; >> + >> + if (!hmm_vma_walk->mmu_range.owner) { >> + mmu_notifier_range_init_owner(&hmm_vma_walk->mmu_range, MMU_NOTIFY_MIGRATE, 0, >> + walk->vma->vm_mm, start, end, >> + range->dev_private_owner); >> + mmu_notifier_invalidate_range_start(&hmm_vma_walk->mmu_range); >> + } >> + >> + return 0; >> +} >> + >> static int hmm_vma_walk_pmd(pmd_t *pmdp, >> unsigned long start, >> unsigned long end, >> @@ -351,13 +625,28 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, >> pmd_migration_entry_wait(walk->mm, pmdp); >> return -EBUSY; >> } >> - return hmm_pfns_fill(start, end, range, 0); >> + return hmm_pfns_fill(start, end, hmm_vma_walk, 0); >> } >> >> if (!pmd_present(pmd)) { >> if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) >> return -EFAULT; >> - return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR); >> + return hmm_pfns_fill(start, end, hmm_vma_walk, HMM_PFN_ERROR); >> + } >> + >> + if (hmm_want_migrate(range) && >> + pmd_trans_huge(pmd)) { >> + int r; >> + >> + r = hmm_vma_walk_split(pmdp, addr, walk); >> + if (r) { >> + /* Split not successful, skip */ >> + return hmm_pfns_fill(start, end, hmm_vma_walk, HMM_PFN_ERROR); >> + } >> + >> + /* Split successful or "again", reloop */ >> + hmm_vma_walk->last = addr; >> + return -EBUSY; >> } >> >> if (pmd_trans_huge(pmd)) { >> @@ -386,7 +675,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, >> if (pmd_bad(pmd)) { >> if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) >> return -EFAULT; >> - return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR); >> + return hmm_pfns_fill(start, end, hmm_vma_walk, HMM_PFN_ERROR); >> } >> >> ptep = pte_offset_map(pmdp, addr); >> @@ -400,8 +689,11 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, >> /* hmm_vma_handle_pte() did pte_unmap() */ >> return r; >> } >> + >> + hmm_vma_handle_migrate_prepare(walk, pmdp, addr, hmm_pfns); >> } >> pte_unmap(ptep - 1); >> + >> return 0; >> } >> >> @@ -535,6 +827,11 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end, >> struct hmm_vma_walk *hmm_vma_walk = walk->private; >> struct hmm_range *range = hmm_vma_walk->range; >> struct vm_area_struct *vma = walk->vma; >> + int r; >> + >> + r = hmm_vma_capture_migrate_range(start, end, walk); >> + if (r) >> + return r; >> >> if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)) && >> vma->vm_flags & VM_READ) >> @@ -557,7 +854,7 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end, >> (end - start) >> PAGE_SHIFT, 0)) >> return -EFAULT; >> >> - hmm_pfns_fill(start, end, range, HMM_PFN_ERROR); >> + hmm_pfns_fill(start, end, hmm_vma_walk, HMM_PFN_ERROR); >> >> /* Skip this vma and continue processing the next vma. */ >> return 1; >> @@ -587,9 +884,17 @@ static const struct mm_walk_ops hmm_walk_ops = { >> * the invalidation to finish. >> * -EFAULT: A page was requested to be valid and could not be made valid >> * ie it has no backing VMA or it is illegal to access >> + * -ERANGE: The range crosses multiple VMAs, or space for hmm_pfns array >> + * is too low. >> * >> * This is similar to get_user_pages(), except that it can read the page tables >> * without mutating them (ie causing faults). >> + * >> + * If want to do migrate after faultin, call hmm_range_fault() with >> + * HMM_PFN_REQ_MIGRATE and initialize range.migrate field. >> + * After hmm_range_fault() call migrate_hmm_range_setup() instead of >> + * migrate_vma_setup() and after that follow normal migrate calls path. >> + * >> */ >> int hmm_range_fault(struct hmm_range *range) >> { >> @@ -597,16 +902,28 @@ int hmm_range_fault(struct hmm_range *range) >> .range = range, >> .last = range->start, >> }; >> - struct mm_struct *mm = range->notifier->mm; >> + bool is_fault_path = !!range->notifier; >> + struct mm_struct *mm; >> int ret; >> >> + /* >> + * >> + * Could be serving a device fault or come from migrate >> + * entry point. For the former we have not resolved the vma >> + * yet, and the latter we don't have a notifier (but have a vma). >> + * >> + */ >> + mm = is_fault_path ? range->notifier->mm : range->migrate->vma->vm_mm; >> mmap_assert_locked(mm); >> >> do { >> /* If range is no longer valid force retry. */ >> - if (mmu_interval_check_retry(range->notifier, >> - range->notifier_seq)) >> - return -EBUSY; >> + if (is_fault_path && mmu_interval_check_retry(range->notifier, >> + range->notifier_seq)) { >> + ret = -EBUSY; >> + break; >> + } >> + >> ret = walk_page_range(mm, hmm_vma_walk.last, range->end, >> &hmm_walk_ops, &hmm_vma_walk); >> /* >> @@ -616,6 +933,18 @@ int hmm_range_fault(struct hmm_range *range) >> * output, and all >= are still at their input values. >> */ >> } while (ret == -EBUSY); >> + >> + if (hmm_want_migrate(range) && range->migrate && >> + hmm_vma_walk.mmu_range.owner) { >> + // The migrate_vma path has the following initialized >> + if (is_fault_path) { >> + range->migrate->vma = hmm_vma_walk.vma; >> + range->migrate->start = range->start; >> + range->migrate->end = hmm_vma_walk.end; >> + } >> + mmu_notifier_invalidate_range_end(&hmm_vma_walk.mmu_range); >> + } >> + >> return ret; >> } >> EXPORT_SYMBOL(hmm_range_fault); >> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >> index e05e14d6eacd..87ddc0353165 100644 >> --- a/mm/migrate_device.c >> +++ b/mm/migrate_device.c >> @@ -535,7 +535,18 @@ 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, >> + .migrate = args, >> + .hmm_pfns = args->src, >> + .default_flags = HMM_PFN_REQ_MIGRATE, >> + .dev_private_owner = args->pgmap_owner, >> + .migrate = args >> + }; >> >> args->start &= PAGE_MASK; >> args->end &= PAGE_MASK; >> @@ -560,17 +571,19 @@ 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; >> >> - if (args->cpages) >> - migrate_vma_unmap(args); >> + ret = hmm_range_fault(&range); >> + >> + migrate_hmm_range_setup(&range); >> >> /* >> * 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); >> @@ -1014,3 +1027,54 @@ int migrate_device_coherent_folio(struct folio *folio) >> return 0; >> return -EBUSY; >> } >> + >> +void migrate_hmm_range_setup(struct hmm_range *range) >> +{ >> + >> + struct migrate_vma *migrate = range->migrate; >> + >> + if (!migrate) >> + return; >> + >> + migrate->npages = (migrate->end - migrate->start) >> PAGE_SHIFT; >> + migrate->cpages = 0; >> + >> + for (unsigned long i = 0; i < migrate->npages; i++) { >> + >> + unsigned long pfn = range->hmm_pfns[i]; >> + >> + /* >> + * >> + * Don't do migration if valid and migrate flags are not both set. >> + * >> + */ >> + if ((pfn & (HMM_PFN_VALID | HMM_PFN_MIGRATE)) != >> + (HMM_PFN_VALID | HMM_PFN_MIGRATE)) { >> + migrate->src[i] = 0; >> + migrate->dst[i] = 0; >> + continue; >> + } >> + >> + migrate->cpages++; >> + >> + /* >> + * >> + * The zero page is encoded in a special way, valid and migrate is >> + * set, and pfn part is zero. Encode specially for migrate also. >> + * >> + */ >> + if (pfn == (HMM_PFN_VALID|HMM_PFN_MIGRATE)) { >> + migrate->src[i] = MIGRATE_PFN_MIGRATE; >> + continue; >> + } >> + >> + migrate->src[i] = migrate_pfn(page_to_pfn(hmm_pfn_to_page(pfn))) >> + | MIGRATE_PFN_MIGRATE; >> + migrate->src[i] |= (pfn & HMM_PFN_WRITE) ? MIGRATE_PFN_WRITE : 0; >> + } >> + >> + if (migrate->cpages) >> + migrate_vma_unmap(migrate); >> + >> +} >> +EXPORT_SYMBOL(migrate_hmm_range_setup); > > I've not had a chance to test the code, do you have any numbers with the changes > to show the advantages of doing both fault and migrate together? Not yet, but plan to have some numbers later. > > Balbir > Thanks, --Mika