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 <david@xxxxxxxxxx>
---
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
