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Thu, 30 Jan 2025 05:46:46 -0800 (PST) Received: from phenom.ffwll.local ([2a02:168:57f4:0:5485:d4b2:c087:b497]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38c5c0ec7e6sm2072886f8f.19.2025.01.30.05.46.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jan 2025 05:46:45 -0800 (PST) Date: Thu, 30 Jan 2025 14:46:43 +0100 From: Simona Vetter To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, Andrew Morton , =?iso-8859-1?B?Suly9G1l?= Glisse , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Alistair Popple , Jason Gunthorpe Subject: Re: [PATCH v1 03/12] mm/rmap: convert make_device_exclusive_range() to make_device_exclusive() Message-ID: Mail-Followup-To: David Hildenbrand , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, Andrew Morton , =?iso-8859-1?B?Suly9G1l?= Glisse , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Alistair Popple , Jason Gunthorpe References: <20250129115411.2077152-1-david@redhat.com> <20250129115411.2077152-4-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250129115411.2077152-4-david@redhat.com> X-Operating-System: Linux phenom 6.12.11-amd64 X-Rspamd-Queue-Id: AC248140016 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: tfpnfws3e6baqducwkqrfxesrkxaek8o X-HE-Tag: 1738244807-152458 X-HE-Meta: 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 LM4GxBUr 9ZjJPTT47pGL/1Lqha6ODo1tz0XWiY4zyL7EpjZisdFf/EFEWMjMoeyDOOxINuJQRSwwEAbqCrxDxA3JguPqr4E4T+c+piaKJpCOtJfNcT46jWBtmZiKCGowM/bAOLebbzqDfWkQTP+CYxqkR56jgmuHrxwwvzUxhL2+pqaW+B+Zi+k0bnsN0RMb7ao2dcqaWTlt1cnpA6sk0sT60TjAe2s5z/38s3JuI911NIDlR51RcW+u7CdGyHM+tVyvwO792TJIHF9Zl2umyg/iyIR8dFxzni9leJ1OkdufW42QXdKGSyXlUyBvSB0NFv8VVW1uKirvbszHTusZo6UCguuHgKN+hOH74iL0K0XGfj93ZDuaXcX8jxhdBohcqB9kZpSO/w4u4pHsS1HCgFyE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jan 29, 2025 at 12:54:01PM +0100, David Hildenbrand wrote: > The single "real" user in the tree of make_device_exclusive_range() always > requests making only a single address exclusive. The current implementation > is hard to fix for properly supporting anonymous THP / large folios and > for avoiding messing with rmap walks in weird ways. > > So let's always process a single address/page and return folio + page to > minimize page -> folio lookups. This is a preparation for further > changes. > > Reject any non-anonymous or hugetlb folios early, directly after GUP. > > Signed-off-by: David Hildenbrand Yeah this makes sense. Even for pmd entries I think we want to make this very explicit with an explicit hugetlb opt-in I think. Acked-by: Simona Vetter > --- > Documentation/mm/hmm.rst | 2 +- > Documentation/translations/zh_CN/mm/hmm.rst | 2 +- > drivers/gpu/drm/nouveau/nouveau_svm.c | 5 +- > include/linux/mmu_notifier.h | 2 +- > include/linux/rmap.h | 5 +- > lib/test_hmm.c | 45 +++++------ > mm/rmap.c | 90 +++++++++++---------- > 7 files changed, 75 insertions(+), 76 deletions(-) > > diff --git a/Documentation/mm/hmm.rst b/Documentation/mm/hmm.rst > index f6d53c37a2ca..7d61b7a8b65b 100644 > --- a/Documentation/mm/hmm.rst > +++ b/Documentation/mm/hmm.rst > @@ -400,7 +400,7 @@ Exclusive access memory > Some devices have features such as atomic PTE bits that can be used to implement > atomic access to system memory. To support atomic operations to a shared virtual > memory page such a device needs access to that page which is exclusive of any > -userspace access from the CPU. The ``make_device_exclusive_range()`` function > +userspace access from the CPU. The ``make_device_exclusive()`` function > can be used to make a memory range inaccessible from userspace. > > This replaces all mappings for pages in the given range with special swap > diff --git a/Documentation/translations/zh_CN/mm/hmm.rst b/Documentation/translations/zh_CN/mm/hmm.rst > index 0669f947d0bc..22c210f4e94f 100644 > --- a/Documentation/translations/zh_CN/mm/hmm.rst > +++ b/Documentation/translations/zh_CN/mm/hmm.rst > @@ -326,7 +326,7 @@ devm_memunmap_pages() 和 devm_release_mem_region() 当资源可以绑定到 ``s > > 一些设备具有诸如原子PTE位的功能，可以用来实现对系统内存的原子访问。为了支持对一 > 个共享的虚拟内存页的原子操作，这样的设备需要对该页的访问是排他的，而不是来自CPU > -的任何用户空间访问。 ``make_device_exclusive_range()`` 函数可以用来使一 > +的任何用户空间访问。 ``make_device_exclusive()`` 函数可以用来使一 > 个内存范围不能从用户空间访问。 > > 这将用特殊的交换条目替换给定范围内的所有页的映射。任何试图访问交换条目的行为都会 > diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c > index b4da82ddbb6b..39e3740980bb 100644 > --- a/drivers/gpu/drm/nouveau/nouveau_svm.c > +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c > @@ -609,10 +609,9 @@ static int nouveau_atomic_range_fault(struct nouveau_svmm *svmm, > > notifier_seq = mmu_interval_read_begin(¬ifier->notifier); > mmap_read_lock(mm); > - ret = make_device_exclusive_range(mm, start, start + PAGE_SIZE, > - &page, drm->dev); > + page = make_device_exclusive(mm, start, drm->dev, &folio); > mmap_read_unlock(mm); > - if (ret <= 0 || !page) { > + if (IS_ERR(page)) { > ret = -EINVAL; > goto out; > } > diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h > index e2dd57ca368b..d4e714661826 100644 > --- a/include/linux/mmu_notifier.h > +++ b/include/linux/mmu_notifier.h > @@ -46,7 +46,7 @@ struct mmu_interval_notifier; > * @MMU_NOTIFY_EXCLUSIVE: to signal a device driver that the device will no > * longer have exclusive access to the page. When sent during creation of an > * exclusive range the owner will be initialised to the value provided by the > - * caller of make_device_exclusive_range(), otherwise the owner will be NULL. > + * caller of make_device_exclusive(), otherwise the owner will be NULL. > */ > enum mmu_notifier_event { > MMU_NOTIFY_UNMAP = 0, > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index 683a04088f3f..86425d42c1a9 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -663,9 +663,8 @@ int folio_referenced(struct folio *, int is_locked, > void try_to_migrate(struct folio *folio, enum ttu_flags flags); > void try_to_unmap(struct folio *, enum ttu_flags flags); > > -int make_device_exclusive_range(struct mm_struct *mm, unsigned long start, > - unsigned long end, struct page **pages, > - void *arg); > +struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr, > + void *owner, struct folio **foliop); > > /* Avoid racy checks */ > #define PVMW_SYNC (1 << 0) > diff --git a/lib/test_hmm.c b/lib/test_hmm.c > index 056f2e411d7b..9e1b07a227a3 100644 > --- a/lib/test_hmm.c > +++ b/lib/test_hmm.c > @@ -780,10 +780,8 @@ static int dmirror_exclusive(struct dmirror *dmirror, > unsigned long start, end, addr; > unsigned long size = cmd->npages << PAGE_SHIFT; > struct mm_struct *mm = dmirror->notifier.mm; > - struct page *pages[64]; > struct dmirror_bounce bounce; > - unsigned long next; > - int ret; > + int ret = 0; > > start = cmd->addr; > end = start + size; > @@ -795,36 +793,31 @@ static int dmirror_exclusive(struct dmirror *dmirror, > return -EINVAL; > > mmap_read_lock(mm); > - for (addr = start; addr < end; addr = next) { > - unsigned long mapped = 0; > - int i; > - > - next = min(end, addr + (ARRAY_SIZE(pages) << PAGE_SHIFT)); > + for (addr = start; addr < end; addr += PAGE_SIZE) { > + struct folio *folio; > + struct page *page; > > - ret = make_device_exclusive_range(mm, addr, next, pages, NULL); > - /* > - * Do dmirror_atomic_map() iff all pages are marked for > - * exclusive access to avoid accessing uninitialized > - * fields of pages. > - */ > - if (ret == (next - addr) >> PAGE_SHIFT) > - mapped = dmirror_atomic_map(addr, next, pages, dmirror); > - for (i = 0; i < ret; i++) { > - if (pages[i]) { > - unlock_page(pages[i]); > - put_page(pages[i]); > - } > + page = make_device_exclusive(mm, addr, &folio, NULL); > + if (IS_ERR(page)) { > + ret = PTR_ERR(page); > + break; > } > > - if (addr + (mapped << PAGE_SHIFT) < next) { > - mmap_read_unlock(mm); > - mmput(mm); > - return -EBUSY; > - } > + ret = dmirror_atomic_map(addr, addr + PAGE_SIZE, &page, dmirror); > + if (!ret) > + ret = -EBUSY; > + folio_unlock(folio); > + folio_put(folio); > + > + if (ret) > + break; > } > mmap_read_unlock(mm); > mmput(mm); > > + if (ret) > + return -EBUSY; > + > /* Return the migrated data for verification. */ > ret = dmirror_bounce_init(&bounce, start, size); > if (ret) > diff --git a/mm/rmap.c b/mm/rmap.c > index 17fbfa61f7ef..676df4fba5b0 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2495,70 +2495,78 @@ static bool folio_make_device_exclusive(struct folio *folio, > .arg = &args, > }; > > - /* > - * Restrict to anonymous folios for now to avoid potential writeback > - * issues. > - */ > - if (!folio_test_anon(folio) || folio_test_hugetlb(folio)) > - return false; > - > rmap_walk(folio, &rwc); > > return args.valid && !folio_mapcount(folio); > } > > /** > - * make_device_exclusive_range() - Mark a range for exclusive use by a device > + * make_device_exclusive() - Mark an address for exclusive use by a device > * @mm: mm_struct of associated target process > - * @start: start of the region to mark for exclusive device access > - * @end: end address of region > - * @pages: returns the pages which were successfully marked for exclusive access > + * @addr: the virtual address to mark for exclusive device access > * @owner: passed to MMU_NOTIFY_EXCLUSIVE range notifier to allow filtering > + * @foliop: folio pointer will be stored here on success. > + * > + * This function looks up the page mapped at the given address, grabs a > + * folio reference, locks the folio and replaces the PTE with special > + * device-exclusive non-swap entry, preventing userspace CPU access. The > + * function will return with the folio locked and referenced. > * > - * Returns: number of pages found in the range by GUP. A page is marked for > - * exclusive access only if the page pointer is non-NULL. > + * On fault these special device-exclusive entries are replaced with the > + * original PTE under folio lock, after calling MMU notifiers. > * > - * This function finds ptes mapping page(s) to the given address range, locks > - * them and replaces mappings with special swap entries preventing userspace CPU > - * access. On fault these entries are replaced with the original mapping after > - * calling MMU notifiers. > + * Only anonymous non-hugetlb folios are supported and the VMA must have > + * write permissions such that we can fault in the anonymous page writable > + * in order to mark it exclusive. The caller must hold the mmap_lock in read > + * mode. > * > * A driver using this to program access from a device must use a mmu notifier > * critical section to hold a device specific lock during programming. Once > * programming is complete it should drop the page lock and reference after > * which point CPU access to the page will revoke the exclusive access. > + * > + * Returns: pointer to mapped page on success, otherwise a negative error. > */ > -int make_device_exclusive_range(struct mm_struct *mm, unsigned long start, > - unsigned long end, struct page **pages, > - void *owner) > +struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr, > + void *owner, struct folio **foliop) > { > - long npages = (end - start) >> PAGE_SHIFT; > - long i; > + struct folio *folio; > + struct page *page; > + long npages; > + > + mmap_assert_locked(mm); > > - npages = get_user_pages_remote(mm, start, npages, > + /* > + * Fault in the page writable and try to lock it; note that if the > + * address would already be marked for exclusive use by the device, > + * the GUP call would undo that first by triggering a fault. > + */ > + npages = get_user_pages_remote(mm, addr, 1, > FOLL_GET | FOLL_WRITE | FOLL_SPLIT_PMD, > - pages, NULL); > - if (npages < 0) > - return npages; > - > - for (i = 0; i < npages; i++, start += PAGE_SIZE) { > - struct folio *folio = page_folio(pages[i]); > - if (PageTail(pages[i]) || !folio_trylock(folio)) { > - folio_put(folio); > - pages[i] = NULL; > - continue; > - } > + &page, NULL); > + if (npages != 1) > + return ERR_PTR(npages); > + folio = page_folio(page); > > - if (!folio_make_device_exclusive(folio, mm, start, owner)) { > - folio_unlock(folio); > - folio_put(folio); > - pages[i] = NULL; > - } > + if (!folio_test_anon(folio) || folio_test_hugetlb(folio)) { > + folio_put(folio); > + return ERR_PTR(-EOPNOTSUPP); > + } > + > + if (!folio_trylock(folio)) { > + folio_put(folio); > + return ERR_PTR(-EBUSY); > } > > - return npages; > + if (!folio_make_device_exclusive(folio, mm, addr, owner)) { > + folio_unlock(folio); > + folio_put(folio); > + return ERR_PTR(-EBUSY); > + } > + *foliop = folio; > + return page; > } > -EXPORT_SYMBOL_GPL(make_device_exclusive_range); > +EXPORT_SYMBOL_GPL(make_device_exclusive); > #endif > > void __put_anon_vma(struct anon_vma *anon_vma) > -- > 2.48.1 > -- Simona Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch