Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma
[platform/kernel/linux-rpi.git] / mm / hugetlb_vmemmap.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * HugeTLB Vmemmap Optimization (HVO)
4  *
5  * Copyright (c) 2020, ByteDance. All rights reserved.
6  *
7  *     Author: Muchun Song <songmuchun@bytedance.com>
8  *
9  * See Documentation/mm/vmemmap_dedup.rst
10  */
11 #define pr_fmt(fmt)     "HugeTLB: " fmt
12
13 #include <linux/pgtable.h>
14 #include <linux/moduleparam.h>
15 #include <linux/bootmem_info.h>
16 #include <asm/pgalloc.h>
17 #include <asm/tlbflush.h>
18 #include "hugetlb_vmemmap.h"
19
20 /**
21  * struct vmemmap_remap_walk - walk vmemmap page table
22  *
23  * @remap_pte:          called for each lowest-level entry (PTE).
24  * @nr_walked:          the number of walked pte.
25  * @reuse_page:         the page which is reused for the tail vmemmap pages.
26  * @reuse_addr:         the virtual address of the @reuse_page page.
27  * @vmemmap_pages:      the list head of the vmemmap pages that can be freed
28  *                      or is mapped from.
29  */
30 struct vmemmap_remap_walk {
31         void                    (*remap_pte)(pte_t *pte, unsigned long addr,
32                                              struct vmemmap_remap_walk *walk);
33         unsigned long           nr_walked;
34         struct page             *reuse_page;
35         unsigned long           reuse_addr;
36         struct list_head        *vmemmap_pages;
37 };
38
39 static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
40 {
41         pmd_t __pmd;
42         int i;
43         unsigned long addr = start;
44         struct page *page = pmd_page(*pmd);
45         pte_t *pgtable = pte_alloc_one_kernel(&init_mm);
46
47         if (!pgtable)
48                 return -ENOMEM;
49
50         pmd_populate_kernel(&init_mm, &__pmd, pgtable);
51
52         for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
53                 pte_t entry, *pte;
54                 pgprot_t pgprot = PAGE_KERNEL;
55
56                 entry = mk_pte(page + i, pgprot);
57                 pte = pte_offset_kernel(&__pmd, addr);
58                 set_pte_at(&init_mm, addr, pte, entry);
59         }
60
61         spin_lock(&init_mm.page_table_lock);
62         if (likely(pmd_leaf(*pmd))) {
63                 /*
64                  * Higher order allocations from buddy allocator must be able to
65                  * be treated as indepdenent small pages (as they can be freed
66                  * individually).
67                  */
68                 if (!PageReserved(page))
69                         split_page(page, get_order(PMD_SIZE));
70
71                 /* Make pte visible before pmd. See comment in pmd_install(). */
72                 smp_wmb();
73                 pmd_populate_kernel(&init_mm, pmd, pgtable);
74                 flush_tlb_kernel_range(start, start + PMD_SIZE);
75         } else {
76                 pte_free_kernel(&init_mm, pgtable);
77         }
78         spin_unlock(&init_mm.page_table_lock);
79
80         return 0;
81 }
82
83 static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
84 {
85         int leaf;
86
87         spin_lock(&init_mm.page_table_lock);
88         leaf = pmd_leaf(*pmd);
89         spin_unlock(&init_mm.page_table_lock);
90
91         if (!leaf)
92                 return 0;
93
94         return __split_vmemmap_huge_pmd(pmd, start);
95 }
96
97 static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
98                               unsigned long end,
99                               struct vmemmap_remap_walk *walk)
100 {
101         pte_t *pte = pte_offset_kernel(pmd, addr);
102
103         /*
104          * The reuse_page is found 'first' in table walk before we start
105          * remapping (which is calling @walk->remap_pte).
106          */
107         if (!walk->reuse_page) {
108                 walk->reuse_page = pte_page(*pte);
109                 /*
110                  * Because the reuse address is part of the range that we are
111                  * walking, skip the reuse address range.
112                  */
113                 addr += PAGE_SIZE;
114                 pte++;
115                 walk->nr_walked++;
116         }
117
118         for (; addr != end; addr += PAGE_SIZE, pte++) {
119                 walk->remap_pte(pte, addr, walk);
120                 walk->nr_walked++;
121         }
122 }
123
124 static int vmemmap_pmd_range(pud_t *pud, unsigned long addr,
125                              unsigned long end,
126                              struct vmemmap_remap_walk *walk)
127 {
128         pmd_t *pmd;
129         unsigned long next;
130
131         pmd = pmd_offset(pud, addr);
132         do {
133                 int ret;
134
135                 ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK);
136                 if (ret)
137                         return ret;
138
139                 next = pmd_addr_end(addr, end);
140                 vmemmap_pte_range(pmd, addr, next, walk);
141         } while (pmd++, addr = next, addr != end);
142
143         return 0;
144 }
145
146 static int vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
147                              unsigned long end,
148                              struct vmemmap_remap_walk *walk)
149 {
150         pud_t *pud;
151         unsigned long next;
152
153         pud = pud_offset(p4d, addr);
154         do {
155                 int ret;
156
157                 next = pud_addr_end(addr, end);
158                 ret = vmemmap_pmd_range(pud, addr, next, walk);
159                 if (ret)
160                         return ret;
161         } while (pud++, addr = next, addr != end);
162
163         return 0;
164 }
165
166 static int vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
167                              unsigned long end,
168                              struct vmemmap_remap_walk *walk)
169 {
170         p4d_t *p4d;
171         unsigned long next;
172
173         p4d = p4d_offset(pgd, addr);
174         do {
175                 int ret;
176
177                 next = p4d_addr_end(addr, end);
178                 ret = vmemmap_pud_range(p4d, addr, next, walk);
179                 if (ret)
180                         return ret;
181         } while (p4d++, addr = next, addr != end);
182
183         return 0;
184 }
185
186 static int vmemmap_remap_range(unsigned long start, unsigned long end,
187                                struct vmemmap_remap_walk *walk)
188 {
189         unsigned long addr = start;
190         unsigned long next;
191         pgd_t *pgd;
192
193         VM_BUG_ON(!PAGE_ALIGNED(start));
194         VM_BUG_ON(!PAGE_ALIGNED(end));
195
196         pgd = pgd_offset_k(addr);
197         do {
198                 int ret;
199
200                 next = pgd_addr_end(addr, end);
201                 ret = vmemmap_p4d_range(pgd, addr, next, walk);
202                 if (ret)
203                         return ret;
204         } while (pgd++, addr = next, addr != end);
205
206         flush_tlb_kernel_range(start, end);
207
208         return 0;
209 }
210
211 /*
212  * Free a vmemmap page. A vmemmap page can be allocated from the memblock
213  * allocator or buddy allocator. If the PG_reserved flag is set, it means
214  * that it allocated from the memblock allocator, just free it via the
215  * free_bootmem_page(). Otherwise, use __free_page().
216  */
217 static inline void free_vmemmap_page(struct page *page)
218 {
219         if (PageReserved(page))
220                 free_bootmem_page(page);
221         else
222                 __free_page(page);
223 }
224
225 /* Free a list of the vmemmap pages */
226 static void free_vmemmap_page_list(struct list_head *list)
227 {
228         struct page *page, *next;
229
230         list_for_each_entry_safe(page, next, list, lru)
231                 free_vmemmap_page(page);
232 }
233
234 static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
235                               struct vmemmap_remap_walk *walk)
236 {
237         /*
238          * Remap the tail pages as read-only to catch illegal write operation
239          * to the tail pages.
240          */
241         pgprot_t pgprot = PAGE_KERNEL_RO;
242         struct page *page = pte_page(*pte);
243         pte_t entry;
244
245         /* Remapping the head page requires r/w */
246         if (unlikely(addr == walk->reuse_addr)) {
247                 pgprot = PAGE_KERNEL;
248                 list_del(&walk->reuse_page->lru);
249
250                 /*
251                  * Makes sure that preceding stores to the page contents from
252                  * vmemmap_remap_free() become visible before the set_pte_at()
253                  * write.
254                  */
255                 smp_wmb();
256         }
257
258         entry = mk_pte(walk->reuse_page, pgprot);
259         list_add_tail(&page->lru, walk->vmemmap_pages);
260         set_pte_at(&init_mm, addr, pte, entry);
261 }
262
263 /*
264  * How many struct page structs need to be reset. When we reuse the head
265  * struct page, the special metadata (e.g. page->flags or page->mapping)
266  * cannot copy to the tail struct page structs. The invalid value will be
267  * checked in the free_tail_page_prepare(). In order to avoid the message
268  * of "corrupted mapping in tail page". We need to reset at least 3 (one
269  * head struct page struct and two tail struct page structs) struct page
270  * structs.
271  */
272 #define NR_RESET_STRUCT_PAGE            3
273
274 static inline void reset_struct_pages(struct page *start)
275 {
276         struct page *from = start + NR_RESET_STRUCT_PAGE;
277
278         BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page));
279         memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE);
280 }
281
282 static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
283                                 struct vmemmap_remap_walk *walk)
284 {
285         pgprot_t pgprot = PAGE_KERNEL;
286         struct page *page;
287         void *to;
288
289         BUG_ON(pte_page(*pte) != walk->reuse_page);
290
291         page = list_first_entry(walk->vmemmap_pages, struct page, lru);
292         list_del(&page->lru);
293         to = page_to_virt(page);
294         copy_page(to, (void *)walk->reuse_addr);
295         reset_struct_pages(to);
296
297         /*
298          * Makes sure that preceding stores to the page contents become visible
299          * before the set_pte_at() write.
300          */
301         smp_wmb();
302         set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
303 }
304
305 /**
306  * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
307  *                      to the page which @reuse is mapped to, then free vmemmap
308  *                      which the range are mapped to.
309  * @start:      start address of the vmemmap virtual address range that we want
310  *              to remap.
311  * @end:        end address of the vmemmap virtual address range that we want to
312  *              remap.
313  * @reuse:      reuse address.
314  *
315  * Return: %0 on success, negative error code otherwise.
316  */
317 static int vmemmap_remap_free(unsigned long start, unsigned long end,
318                               unsigned long reuse)
319 {
320         int ret;
321         LIST_HEAD(vmemmap_pages);
322         struct vmemmap_remap_walk walk = {
323                 .remap_pte      = vmemmap_remap_pte,
324                 .reuse_addr     = reuse,
325                 .vmemmap_pages  = &vmemmap_pages,
326         };
327         int nid = page_to_nid((struct page *)start);
328         gfp_t gfp_mask = GFP_KERNEL | __GFP_THISNODE | __GFP_NORETRY |
329                         __GFP_NOWARN;
330
331         /*
332          * Allocate a new head vmemmap page to avoid breaking a contiguous
333          * block of struct page memory when freeing it back to page allocator
334          * in free_vmemmap_page_list(). This will allow the likely contiguous
335          * struct page backing memory to be kept contiguous and allowing for
336          * more allocations of hugepages. Fallback to the currently
337          * mapped head page in case should it fail to allocate.
338          */
339         walk.reuse_page = alloc_pages_node(nid, gfp_mask, 0);
340         if (walk.reuse_page) {
341                 copy_page(page_to_virt(walk.reuse_page),
342                           (void *)walk.reuse_addr);
343                 list_add(&walk.reuse_page->lru, &vmemmap_pages);
344         }
345
346         /*
347          * In order to make remapping routine most efficient for the huge pages,
348          * the routine of vmemmap page table walking has the following rules
349          * (see more details from the vmemmap_pte_range()):
350          *
351          * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
352          *   should be continuous.
353          * - The @reuse address is part of the range [@reuse, @end) that we are
354          *   walking which is passed to vmemmap_remap_range().
355          * - The @reuse address is the first in the complete range.
356          *
357          * So we need to make sure that @start and @reuse meet the above rules.
358          */
359         BUG_ON(start - reuse != PAGE_SIZE);
360
361         mmap_read_lock(&init_mm);
362         ret = vmemmap_remap_range(reuse, end, &walk);
363         if (ret && walk.nr_walked) {
364                 end = reuse + walk.nr_walked * PAGE_SIZE;
365                 /*
366                  * vmemmap_pages contains pages from the previous
367                  * vmemmap_remap_range call which failed.  These
368                  * are pages which were removed from the vmemmap.
369                  * They will be restored in the following call.
370                  */
371                 walk = (struct vmemmap_remap_walk) {
372                         .remap_pte      = vmemmap_restore_pte,
373                         .reuse_addr     = reuse,
374                         .vmemmap_pages  = &vmemmap_pages,
375                 };
376
377                 vmemmap_remap_range(reuse, end, &walk);
378         }
379         mmap_read_unlock(&init_mm);
380
381         free_vmemmap_page_list(&vmemmap_pages);
382
383         return ret;
384 }
385
386 static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
387                                    gfp_t gfp_mask, struct list_head *list)
388 {
389         unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
390         int nid = page_to_nid((struct page *)start);
391         struct page *page, *next;
392
393         while (nr_pages--) {
394                 page = alloc_pages_node(nid, gfp_mask, 0);
395                 if (!page)
396                         goto out;
397                 list_add_tail(&page->lru, list);
398         }
399
400         return 0;
401 out:
402         list_for_each_entry_safe(page, next, list, lru)
403                 __free_page(page);
404         return -ENOMEM;
405 }
406
407 /**
408  * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
409  *                       to the page which is from the @vmemmap_pages
410  *                       respectively.
411  * @start:      start address of the vmemmap virtual address range that we want
412  *              to remap.
413  * @end:        end address of the vmemmap virtual address range that we want to
414  *              remap.
415  * @reuse:      reuse address.
416  * @gfp_mask:   GFP flag for allocating vmemmap pages.
417  *
418  * Return: %0 on success, negative error code otherwise.
419  */
420 static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
421                                unsigned long reuse, gfp_t gfp_mask)
422 {
423         LIST_HEAD(vmemmap_pages);
424         struct vmemmap_remap_walk walk = {
425                 .remap_pte      = vmemmap_restore_pte,
426                 .reuse_addr     = reuse,
427                 .vmemmap_pages  = &vmemmap_pages,
428         };
429
430         /* See the comment in the vmemmap_remap_free(). */
431         BUG_ON(start - reuse != PAGE_SIZE);
432
433         if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
434                 return -ENOMEM;
435
436         mmap_read_lock(&init_mm);
437         vmemmap_remap_range(reuse, end, &walk);
438         mmap_read_unlock(&init_mm);
439
440         return 0;
441 }
442
443 DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
444 EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
445
446 static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
447 core_param(hugetlb_free_vmemmap, vmemmap_optimize_enabled, bool, 0);
448
449 /**
450  * hugetlb_vmemmap_restore - restore previously optimized (by
451  *                           hugetlb_vmemmap_optimize()) vmemmap pages which
452  *                           will be reallocated and remapped.
453  * @h:          struct hstate.
454  * @head:       the head page whose vmemmap pages will be restored.
455  *
456  * Return: %0 if @head's vmemmap pages have been reallocated and remapped,
457  * negative error code otherwise.
458  */
459 int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
460 {
461         int ret;
462         unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
463         unsigned long vmemmap_reuse;
464
465         if (!HPageVmemmapOptimized(head))
466                 return 0;
467
468         vmemmap_end     = vmemmap_start + hugetlb_vmemmap_size(h);
469         vmemmap_reuse   = vmemmap_start;
470         vmemmap_start   += HUGETLB_VMEMMAP_RESERVE_SIZE;
471
472         /*
473          * The pages which the vmemmap virtual address range [@vmemmap_start,
474          * @vmemmap_end) are mapped to are freed to the buddy allocator, and
475          * the range is mapped to the page which @vmemmap_reuse is mapped to.
476          * When a HugeTLB page is freed to the buddy allocator, previously
477          * discarded vmemmap pages must be allocated and remapping.
478          */
479         ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse,
480                                   GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
481         if (!ret) {
482                 ClearHPageVmemmapOptimized(head);
483                 static_branch_dec(&hugetlb_optimize_vmemmap_key);
484         }
485
486         return ret;
487 }
488
489 /* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
490 static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
491 {
492         if (!READ_ONCE(vmemmap_optimize_enabled))
493                 return false;
494
495         if (!hugetlb_vmemmap_optimizable(h))
496                 return false;
497
498         if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
499                 pmd_t *pmdp, pmd;
500                 struct page *vmemmap_page;
501                 unsigned long vaddr = (unsigned long)head;
502
503                 /*
504                  * Only the vmemmap page's vmemmap page can be self-hosted.
505                  * Walking the page tables to find the backing page of the
506                  * vmemmap page.
507                  */
508                 pmdp = pmd_off_k(vaddr);
509                 /*
510                  * The READ_ONCE() is used to stabilize *pmdp in a register or
511                  * on the stack so that it will stop changing under the code.
512                  * The only concurrent operation where it can be changed is
513                  * split_vmemmap_huge_pmd() (*pmdp will be stable after this
514                  * operation).
515                  */
516                 pmd = READ_ONCE(*pmdp);
517                 if (pmd_leaf(pmd))
518                         vmemmap_page = pmd_page(pmd) + pte_index(vaddr);
519                 else
520                         vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr));
521                 /*
522                  * Due to HugeTLB alignment requirements and the vmemmap pages
523                  * being at the start of the hotplugged memory region in
524                  * memory_hotplug.memmap_on_memory case. Checking any vmemmap
525                  * page's vmemmap page if it is marked as VmemmapSelfHosted is
526                  * sufficient.
527                  *
528                  * [                  hotplugged memory                  ]
529                  * [        section        ][...][        section        ]
530                  * [ vmemmap ][              usable memory               ]
531                  *   ^   |     |                                        |
532                  *   +---+     |                                        |
533                  *     ^       |                                        |
534                  *     +-------+                                        |
535                  *          ^                                           |
536                  *          +-------------------------------------------+
537                  */
538                 if (PageVmemmapSelfHosted(vmemmap_page))
539                         return false;
540         }
541
542         return true;
543 }
544
545 /**
546  * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
547  * @h:          struct hstate.
548  * @head:       the head page whose vmemmap pages will be optimized.
549  *
550  * This function only tries to optimize @head's vmemmap pages and does not
551  * guarantee that the optimization will succeed after it returns. The caller
552  * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
553  * have been optimized.
554  */
555 void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
556 {
557         unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
558         unsigned long vmemmap_reuse;
559
560         if (!vmemmap_should_optimize(h, head))
561                 return;
562
563         static_branch_inc(&hugetlb_optimize_vmemmap_key);
564
565         vmemmap_end     = vmemmap_start + hugetlb_vmemmap_size(h);
566         vmemmap_reuse   = vmemmap_start;
567         vmemmap_start   += HUGETLB_VMEMMAP_RESERVE_SIZE;
568
569         /*
570          * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
571          * to the page which @vmemmap_reuse is mapped to, then free the pages
572          * which the range [@vmemmap_start, @vmemmap_end] is mapped to.
573          */
574         if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
575                 static_branch_dec(&hugetlb_optimize_vmemmap_key);
576         else
577                 SetHPageVmemmapOptimized(head);
578 }
579
580 static struct ctl_table hugetlb_vmemmap_sysctls[] = {
581         {
582                 .procname       = "hugetlb_optimize_vmemmap",
583                 .data           = &vmemmap_optimize_enabled,
584                 .maxlen         = sizeof(vmemmap_optimize_enabled),
585                 .mode           = 0644,
586                 .proc_handler   = proc_dobool,
587         },
588         { }
589 };
590
591 static int __init hugetlb_vmemmap_init(void)
592 {
593         const struct hstate *h;
594
595         /* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */
596         BUILD_BUG_ON(__NR_USED_SUBPAGE * sizeof(struct page) > HUGETLB_VMEMMAP_RESERVE_SIZE);
597
598         for_each_hstate(h) {
599                 if (hugetlb_vmemmap_optimizable(h)) {
600                         register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
601                         break;
602                 }
603         }
604         return 0;
605 }
606 late_initcall(hugetlb_vmemmap_init);