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[2003:cb:c734:b800:12c4:65cd:348a:aee6]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-4390d94d802sm195253865e9.12.2025.02.10.11.38.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Feb 2025 11:38:15 -0800 (PST) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, damon@lists.linux.dev, David Hildenbrand , Andrew Morton , =?utf-8?b?SsOpcsO0bWUgR2xpc3Nl?= , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , SeongJae Park , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Alistair Popple , Jason Gunthorpe , Simona Vetter Subject: [PATCH v2 03/17] mm/rmap: convert make_device_exclusive_range() to make_device_exclusive() Date: Mon, 10 Feb 2025 20:37:45 +0100 Message-ID: <20250210193801.781278-4-david@redhat.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250210193801.781278-1-david@redhat.com> References: <20250210193801.781278-1-david@redhat.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: QTPBoFjlV_ax190JFnuqp5Y9TM57b3UFEjvE3bKiScI_1739216297 X-Mimecast-Originator: redhat.com 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. While at it, extend the documentation of make_device_exclusive() to clarify some things. Acked-by: Simona Vetter Reviewed-by: Alistair Popple Signed-off-by: David Hildenbrand Signed-off-by: David Hildenbrand --- 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 | 41 +++----- mm/rmap.c | 103 ++++++++++++-------- 7 files changed, 83 insertions(+), 77 deletions(-) diff --git a/Documentation/mm/hmm.rst b/Documentation/mm/hmm.rst index f6d53c37a2ca8..7d61b7a8b65b7 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 0669f947d0bc9..22c210f4e94f3 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 b4da82ddbb6b2..39e3740980bb7 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 e2dd57ca368b0..d4e7146618262 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 683a04088f3f2..86425d42c1a90 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 056f2e411d7b4..e4afca8d18802 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 +793,27 @@ 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; !ret && 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, NULL, &folio); + 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); + ret = ret == 1 ? 0 : -EBUSY; + folio_unlock(folio); + folio_put(folio); } mmap_read_unlock(mm); mmput(mm); + if (ret) + return ret; + /* 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 17fbfa61f7efb..7ccf850565d33 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -2495,70 +2495,89 @@ 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 a page 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 PFN swap entry, preventing access through the process + * page tables. 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, the 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 + * programming is complete it should drop the folio lock and reference after * which point CPU access to the page will revoke the exclusive access. + * + * Notes: + * #. This function always operates on individual PTEs mapping individual + * pages. PMD-sized THPs are first remapped to be mapped by PTEs before + * the conversion happens on a single PTE corresponding to @addr. + * #. While concurrent access through the process page tables is prevented, + * concurrent access through other page references (e.g., earlier GUP + * invocation) is not handled and not supported. + * #. device-exclusive entries are considered "clean" and "old" by core-mm. + * Device drivers must update the folio state when informed by MMU + * notifiers. + * + * 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 a 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)