Merge tag 'mm-stable-2022-08-09' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull remaining MM updates from Andrew Morton:
 "Three patch series - two that perform cleanups and one feature:

   - hugetlb_vmemmap cleanups from Muchun Song

   - hardware poisoning support for 1GB hugepages, from Naoya Horiguchi

   - highmem documentation fixups from Fabio De Francesco"

* tag 'mm-stable-2022-08-09' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (23 commits)
  Documentation/mm: add details about kmap_local_page() and preemption
  highmem: delete a sentence from kmap_local_page() kdocs
  Documentation/mm: rrefer kmap_local_page() and avoid kmap()
  Documentation/mm: avoid invalid use of addresses from kmap_local_page()
  Documentation/mm: don't kmap*() pages which can't come from HIGHMEM
  highmem: specify that kmap_local_page() is callable from interrupts
  highmem: remove unneeded spaces in kmap_local_page() kdocs
  mm, hwpoison: enable memory error handling on 1GB hugepage
  mm, hwpoison: skip raw hwpoison page in freeing 1GB hugepage
  mm, hwpoison: make __page_handle_poison returns int
  mm, hwpoison: set PG_hwpoison for busy hugetlb pages
  mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage
  mm, hwpoison, hugetlb: support saving mechanism of raw error pages
  mm/hugetlb: make pud_huge() and follow_huge_pud() aware of non-present pud entry
  mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages()
  mm: hugetlb_vmemmap: use PTRS_PER_PTE instead of PMD_SIZE / PAGE_SIZE
  mm: hugetlb_vmemmap: move code comments to vmemmap_dedup.rst
  mm: hugetlb_vmemmap: improve hugetlb_vmemmap code readability
  mm: hugetlb_vmemmap: replace early_param() with core_param()
  mm: hugetlb_vmemmap: move vmemmap code related to HugeTLB to hugetlb_vmemmap.c
  ...

Author: torvalds

Documentation/admin-guide/kernel-parameters.txt

@@ -1735,12 +1735,13 @@
 	hugetlb_free_vmemmap=
 			[KNL] Reguires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 			enabled.
+			Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
 			Allows heavy hugetlb users to free up some more
 			memory (7 * PAGE_SIZE for each 2MB hugetlb page).
-			Format: { [oO][Nn]/Y/y/1 | [oO][Ff]/N/n/0 (default) }
+			Format: { on | off (default) }
 
-			[oO][Nn]/Y/y/1: enable the feature
-			[oO][Ff]/N/n/0: disable the feature
+			on: enable HVO
+			off: disable HVO
 
 			Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
 			the default is on.

Documentation/admin-guide/mm/hugetlbpage.rst

@@ -164,8 +164,8 @@ default_hugepagesz
 	will all result in 256 2M huge pages being allocated.  Valid default
 	huge page size is architecture dependent.
 hugetlb_free_vmemmap
-	When CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is set, this enables optimizing
-	unused vmemmap pages associated with each HugeTLB page.
+	When CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is set, this enables HugeTLB
+	Vmemmap Optimization (HVO).
 
 When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages``
 indicates the current number of pre-allocated huge pages of the default size.

Documentation/admin-guide/mm/memory-hotplug.rst

@@ -653,8 +653,8 @@ block might fail:
 - Concurrent activity that operates on the same physical memory area, such as
   allocating gigantic pages, can result in temporary offlining failures.
 
-- Out of memory when dissolving huge pages, especially when freeing unused
-  vmemmap pages associated with each hugetlb page is enabled.
+- Out of memory when dissolving huge pages, especially when HugeTLB Vmemmap
+  Optimization (HVO) is enabled.
 
   Offlining code may be able to migrate huge page contents, but may not be able
   to dissolve the source huge page because it fails allocating (unmovable) pages

Documentation/admin-guide/sysctl/vm.rst

@@ -569,8 +569,7 @@ This knob is not available when the size of 'struct page' (a structure defined
 in include/linux/mm_types.h) is not power of two (an unusual system config could
 result in this).
 
-Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages
-associated with each HugeTLB page.
+Enable (set to 1) or disable (set to 0) HugeTLB Vmemmap Optimization (HVO).
 
 Once enabled, the vmemmap pages of subsequent allocation of HugeTLB pages from
 buddy allocator will be optimized (7 pages per 2MB HugeTLB page and 4095 pages

Documentation/mm/highmem.rst

@@ -60,17 +60,40 @@ list shows them in order of preference of use.
   This function should be preferred, where feasible, over all the others.
 
   These mappings are thread-local and CPU-local, meaning that the mapping
-  can only be accessed from within this thread and the thread is bound the
-  CPU while the mapping is active. Even if the thread is preempted (since
-  preemption is never disabled by the function) the CPU can not be
-  unplugged from the system via CPU-hotplug until the mapping is disposed.
+  can only be accessed from within this thread and the thread is bound to the
+  CPU while the mapping is active. Although preemption is never disabled by
+  this function, the CPU can not be unplugged from the system via
+  CPU-hotplug until the mapping is disposed.
 
   It's valid to take pagefaults in a local kmap region, unless the context
   in which the local mapping is acquired does not allow it for other reasons.
 
+  As said, pagefaults and preemption are never disabled. There is no need to
+  disable preemption because, when context switches to a different task, the
+  maps of the outgoing task are saved and those of the incoming one are
+  restored.
+
   kmap_local_page() always returns a valid virtual address and it is assumed
   that kunmap_local() will never fail.
 
+  On CONFIG_HIGHMEM=n kernels and for low memory pages this returns the
+  virtual address of the direct mapping. Only real highmem pages are
+  temporarily mapped. Therefore, users may call a plain page_address()
+  for pages which are known to not come from ZONE_HIGHMEM. However, it is
+  always safe to use kmap_local_page() / kunmap_local().
+
+  While it is significantly faster than kmap(), for the higmem case it
+  comes with restrictions about the pointers validity. Contrary to kmap()
+  mappings, the local mappings are only valid in the context of the caller
+  and cannot be handed to other contexts. This implies that users must
+  be absolutely sure to keep the use of the return address local to the
+  thread which mapped it.
+
+  Most code can be designed to use thread local mappings. User should
+  therefore try to design their code to avoid the use of kmap() by mapping
+  pages in the same thread the address will be used and prefer
+  kmap_local_page().
+
   Nesting kmap_local_page() and kmap_atomic() mappings is allowed to a certain
   extent (up to KMAP_TYPE_NR) but their invocations have to be strictly ordered
   because the map implementation is stack based. See kmap_local_page() kdocs

Documentation/mm/vmemmap_dedup.rst

@@ -7,23 +7,25 @@ A vmemmap diet for HugeTLB and Device DAX
 HugeTLB
 =======
 
-The struct page structures (page structs) are used to describe a physical
-page frame. By default, there is a one-to-one mapping from a page frame to
-it's corresponding page struct.
+This section is to explain how HugeTLB Vmemmap Optimization (HVO) works.
+
+The ``struct page`` structures are used to describe a physical page frame. By
+default, there is a one-to-one mapping from a page frame to it's corresponding
+``struct page``.
 
 HugeTLB pages consist of multiple base page size pages and is supported by many
 architectures. See Documentation/admin-guide/mm/hugetlbpage.rst for more
 details. On the x86-64 architecture, HugeTLB pages of size 2MB and 1GB are
 currently supported. Since the base page size on x86 is 4KB, a 2MB HugeTLB page
 consists of 512 base pages and a 1GB HugeTLB page consists of 4096 base pages.
-For each base page, there is a corresponding page struct.
+For each base page, there is a corresponding ``struct page``.
 
-Within the HugeTLB subsystem, only the first 4 page structs are used to
-contain unique information about a HugeTLB page. __NR_USED_SUBPAGE provides
-this upper limit. The only 'useful' information in the remaining page structs
+Within the HugeTLB subsystem, only the first 4 ``struct page`` are used to
+contain unique information about a HugeTLB page. ``__NR_USED_SUBPAGE`` provides
+this upper limit. The only 'useful' information in the remaining ``struct page``
 is the compound_head field, and this field is the same for all tail pages.
 
-By removing redundant page structs for HugeTLB pages, memory can be returned
+By removing redundant ``struct page`` for HugeTLB pages, memory can be returned
 to the buddy allocator for other uses.
 
 Different architectures support different HugeTLB pages. For example, the
@@ -44,7 +46,7 @@ page.
 |              |   64KB    |    2MB    |  512MB    |    16GB   |           |
 +--------------+-----------+-----------+-----------+-----------+-----------+
 
-When the system boot up, every HugeTLB page has more than one struct page
+When the system boot up, every HugeTLB page has more than one ``struct page``
 structs which size is (unit: pages)::
 
    struct_size = HugeTLB_Size / PAGE_SIZE * sizeof(struct page) / PAGE_SIZE
@@ -74,10 +76,10 @@ Where n is how many pte entries which one page can contains. So the value of
 n is (PAGE_SIZE / sizeof(pte_t)).
 
 This optimization only supports 64-bit system, so the value of sizeof(pte_t)
-is 8. And this optimization also applicable only when the size of struct page
-is a power of two. In most cases, the size of struct page is 64 bytes (e.g.
+is 8. And this optimization also applicable only when the size of ``struct page``
+is a power of two. In most cases, the size of ``struct page`` is 64 bytes (e.g.
 x86-64 and arm64). So if we use pmd level mapping for a HugeTLB page, the
-size of struct page structs of it is 8 page frames which size depends on the
+size of ``struct page`` structs of it is 8 page frames which size depends on the
 size of the base page.
 
 For the HugeTLB page of the pud level mapping, then::
@@ -86,15 +88,15 @@ For the HugeTLB page of the pud level mapping, then::
                = PAGE_SIZE / 8 * 8 (pages)
                = PAGE_SIZE (pages)
 
-Where the struct_size(pmd) is the size of the struct page structs of a
+Where the struct_size(pmd) is the size of the ``struct page`` structs of a
 HugeTLB page of the pmd level mapping.
 
 E.g.: A 2MB HugeTLB page on x86_64 consists in 8 page frames while 1GB
 HugeTLB page consists in 4096.
 
 Next, we take the pmd level mapping of the HugeTLB page as an example to
 show the internal implementation of this optimization. There are 8 pages
-struct page structs associated with a HugeTLB page which is pmd mapped.
+``struct page`` structs associated with a HugeTLB page which is pmd mapped.
 
 Here is how things look before optimization::
 
@@ -122,10 +124,10 @@ Here is how things look before optimization::
  +-----------+
 
 The value of page->compound_head is the same for all tail pages. The first
-page of page structs (page 0) associated with the HugeTLB page contains the 4
-page structs necessary to describe the HugeTLB. The only use of the remaining
-pages of page structs (page 1 to page 7) is to point to page->compound_head.
-Therefore, we can remap pages 1 to 7 to page 0. Only 1 page of page structs
+page of ``struct page`` (page 0) associated with the HugeTLB page contains the 4
+``struct page`` necessary to describe the HugeTLB. The only use of the remaining
+pages of ``struct page`` (page 1 to page 7) is to point to page->compound_head.
+Therefore, we can remap pages 1 to 7 to page 0. Only 1 page of ``struct page``
 will be used for each HugeTLB page. This will allow us to free the remaining
 7 pages to the buddy allocator.
 
@@ -167,13 +169,37 @@ entries that can be cached in a single TLB entry.
 
 The contiguous bit is used to increase the mapping size at the pmd and pte
 (last) level. So this type of HugeTLB page can be optimized only when its
-size of the struct page structs is greater than 1 page.
+size of the ``struct page`` structs is greater than **1** page.
 
 Notice: The head vmemmap page is not freed to the buddy allocator and all
 tail vmemmap pages are mapped to the head vmemmap page frame. So we can see
-more than one struct page struct with PG_head (e.g. 8 per 2 MB HugeTLB page)
-associated with each HugeTLB page. The compound_head() can handle this
-correctly (more details refer to the comment above compound_head()).
+more than one ``struct page`` struct with ``PG_head`` (e.g. 8 per 2 MB HugeTLB
+page) associated with each HugeTLB page. The ``compound_head()`` can handle
+this correctly. There is only **one** head ``struct page``, the tail
+``struct page`` with ``PG_head`` are fake head ``struct page``.  We need an
+approach to distinguish between those two different types of ``struct page`` so
+that ``compound_head()`` can return the real head ``struct page`` when the
+parameter is the tail ``struct page`` but with ``PG_head``. The following code
+snippet describes how to distinguish between real and fake head ``struct page``.
+
+.. code-block:: c
+
+	if (test_bit(PG_head, &page->flags)) {
+		unsigned long head = READ_ONCE(page[1].compound_head);
+
+		if (head & 1) {
+			if (head == (unsigned long)page + 1)
+				/* head struct page */
+			else
+				/* tail struct page */
+		} else {
+			/* head struct page */
+		}
+	}
+
+We can safely access the field of the **page[1]** with ``PG_head`` because the
+page is a compound page composed with at least two contiguous pages.
+The implementation refers to ``page_fixed_fake_head()``.
 
 Device DAX
 ==========
@@ -187,7 +213,7 @@ PMD_SIZE (2M on x86_64) and PUD_SIZE (1G on x86_64).
 
 The differences with HugeTLB are relatively minor.
 
-It only use 3 page structs for storing all information as opposed
+It only use 3 ``struct page`` for storing all information as opposed
 to 4 on HugeTLB pages.
 
 There's no remapping of vmemmap given that device-dax memory is not part of

arch/arm64/mm/flush.c

@@ -76,17 +76,10 @@ EXPORT_SYMBOL_GPL(__sync_icache_dcache);
 void flush_dcache_page(struct page *page)
 {
 	/*
-	 * Only the head page's flags of HugeTLB can be cleared since the tail
-	 * vmemmap pages associated with each HugeTLB page are mapped with
-	 * read-only when CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is enabled (more
-	 * details can refer to vmemmap_remap_pte()).  Although
-	 * __sync_icache_dcache() only set PG_dcache_clean flag on the head
-	 * page struct, there is more than one page struct with PG_dcache_clean
-	 * associated with the HugeTLB page since the head vmemmap page frame
-	 * is reused (more details can refer to the comments above
-	 * page_fixed_fake_head()).
+	 * HugeTLB pages are always fully mapped and only head page will be
+	 * set PG_dcache_clean (see comments in __sync_icache_dcache()).
 	 */
-	if (hugetlb_optimize_vmemmap_enabled() && PageHuge(page))
+	if (PageHuge(page))
 		page = compound_head(page);
 
 	if (test_bit(PG_dcache_clean, &page->flags))

arch/x86/mm/hugetlbpage.c

@@ -30,9 +30,15 @@ int pmd_huge(pmd_t pmd)
 		(pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
 }
 
+/*
+ * pud_huge() returns 1 if @pud is hugetlb related entry, that is normal
+ * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry.
+ * Otherwise, returns 0.
+ */
 int pud_huge(pud_t pud)
 {
-	return !!(pud_val(pud) & _PAGE_PSE);
+	return !pud_none(pud) &&
+		(pud_val(pud) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
 }
 
 #ifdef CONFIG_HUGETLB_PAGE

fs/Kconfig

@@ -247,8 +247,7 @@ config HUGETLB_PAGE
 
 #
 # Select this config option from the architecture Kconfig, if it is preferred
-# to enable the feature of minimizing overhead of struct page associated with
-# each HugeTLB page.
+# to enable the feature of HugeTLB Vmemmap Optimization (HVO).
 #
 config ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	bool
@@ -259,14 +258,13 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	depends on SPARSEMEM_VMEMMAP
 
 config HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON
-	bool "Default optimizing vmemmap pages of HugeTLB to on"
+	bool "HugeTLB Vmemmap Optimization (HVO) defaults to on"
 	default n
 	depends on HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	help
-	  When using HUGETLB_PAGE_OPTIMIZE_VMEMMAP, the optimizing unused vmemmap
-	  pages associated with each HugeTLB page is default off. Say Y here
-	  to enable optimizing vmemmap pages of HugeTLB by default. It can then
-	  be disabled on the command line via hugetlb_free_vmemmap=off.
+	  The HugeTLB VmemmapvOptimization (HVO) defaults to off. Say Y here to
+	  enable HVO by default. It can be disabled via hugetlb_free_vmemmap=off
+	  (boot command line) or hugetlb_optimize_vmemmap (sysctl).
 
 config MEMFD_CREATE
 	def_bool TMPFS || HUGETLBFS

include/linux/highmem.h

@@ -60,11 +60,11 @@ static inline void kmap_flush_unused(void);
 
 /**
  * kmap_local_page - Map a page for temporary usage
- * @page:	Pointer to the page to be mapped
+ * @page: Pointer to the page to be mapped
  *
  * Returns: The virtual address of the mapping
  *
- * Can be invoked from any context.
+ * Can be invoked from any context, including interrupts.
  *
  * Requires careful handling when nesting multiple mappings because the map
  * management is stack based. The unmap has to be in the reverse order of
@@ -86,8 +86,7 @@ static inline void kmap_flush_unused(void);
  * temporarily mapped.
  *
  * While it is significantly faster than kmap() for the higmem case it
- * comes with restrictions about the pointer validity. Only use when really
- * necessary.
+ * comes with restrictions about the pointer validity.
  *
  * On HIGHMEM enabled systems mapping a highmem page has the side effect of
  * disabling migration in order to keep the virtual address stable across