mm/mmu_gather.c

   1 #include <linux/gfp.h>
   2 #include <linux/highmem.h>
   3 #include <linux/kernel.h>
   4 #include <linux/mmdebug.h>
   5 #include <linux/mm_types.h>
   6 #include <linux/pagemap.h>
   7 #include <linux/rcupdate.h>
   8 #include <linux/smp.h>
   9 #include <linux/swap.h>
  10
  11 #include <asm/pgalloc.h>
  12 #include <asm/tlb.h>
  13
  14 #ifndef CONFIG_MMU_GATHER_NO_GATHER
  15
  16 static bool tlb_next_batch(struct mmu_gather *tlb)
  17 {
  18         struct mmu_gather_batch *batch;
  19
  20         batch = tlb->active;
  21         if (batch->next) {
  22                 tlb->active = batch->next;
  23                 return true;
  24         }
  25
  26         if (tlb->batch_count == MAX_GATHER_BATCH_COUNT)
  27                 return false;
  28
  29         batch = (void *)__get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
  30         if (!batch)
  31                 return false;
  32
  33         tlb->batch_count++;
  34         batch->next = NULL;
  35         batch->nr   = 0;
  36         batch->max  = MAX_GATHER_BATCH;
  37
  38         tlb->active->next = batch;
  39         tlb->active = batch;
  40
  41         return true;
  42 }
  43
  44 static void tlb_batch_pages_flush(struct mmu_gather *tlb)
  45 {
  46         struct mmu_gather_batch *batch;
  47
  48         for (batch = &tlb->local; batch && batch->nr; batch = batch->next) {
  49                 free_pages_and_swap_cache(batch->pages, batch->nr);
  50                 batch->nr = 0;
  51         }
  52         tlb->active = &tlb->local;
  53 }
  54
  55 static void tlb_batch_list_free(struct mmu_gather *tlb)
  56 {
  57         struct mmu_gather_batch *batch, *next;
  58
  59         for (batch = tlb->local.next; batch; batch = next) {
  60                 next = batch->next;
  61                 free_pages((unsigned long)batch, 0);
  62         }
  63         tlb->local.next = NULL;
  64 }
  65
  66 bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_size)
  67 {
  68         struct mmu_gather_batch *batch;
  69
  70         VM_BUG_ON(!tlb->end);
  71
  72 #ifdef CONFIG_MMU_GATHER_PAGE_SIZE
  73         VM_WARN_ON(tlb->page_size != page_size);
  74 #endif
  75
  76         batch = tlb->active;
  77         /*
  78          * Add the page and check if we are full. If so
  79          * force a flush.
  80          */
  81         batch->pages[batch->nr++] = page;
  82         if (batch->nr == batch->max) {
  83                 if (!tlb_next_batch(tlb))
  84                         return true;
  85                 batch = tlb->active;
  86         }
  87         VM_BUG_ON_PAGE(batch->nr > batch->max, page);
  88
  89         return false;
  90 }
  91
  92 #endif /* MMU_GATHER_NO_GATHER */
  93
  94 #ifdef CONFIG_MMU_GATHER_TABLE_FREE
  95
  96 static void __tlb_remove_table_free(struct mmu_table_batch *batch)
  97 {
  98         int i;
  99
 100         for (i = 0; i < batch->nr; i++)
 101                 __tlb_remove_table(batch->tables[i]);
 102
 103         free_page((unsigned long)batch);
 104 }
 105
 106 #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
 107
 108 /*
 109  * Semi RCU freeing of the page directories.
 110  *
 111  * This is needed by some architectures to implement software pagetable walkers.
 112  *
 113  * gup_fast() and other software pagetable walkers do a lockless page-table
 114  * walk and therefore needs some synchronization with the freeing of the page
 115  * directories. The chosen means to accomplish that is by disabling IRQs over
 116  * the walk.
 117  *
 118  * Architectures that use IPIs to flush TLBs will then automagically DTRT,
 119  * since we unlink the page, flush TLBs, free the page. Since the disabling of
 120  * IRQs delays the completion of the TLB flush we can never observe an already
 121  * freed page.
 122  *
 123  * Architectures that do not have this (PPC) need to delay the freeing by some
 124  * other means, this is that means.
 125  *
 126  * What we do is batch the freed directory pages (tables) and RCU free them.
 127  * We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
 128  * holds off grace periods.
 129  *
 130  * However, in order to batch these pages we need to allocate storage, this
 131  * allocation is deep inside the MM code and can thus easily fail on memory
 132  * pressure. To guarantee progress we fall back to single table freeing, see
 133  * the implementation of tlb_remove_table_one().
 134  *
 135  */
 136
 137 static void tlb_remove_table_smp_sync(void *arg)
 138 {
 139         /* Simply deliver the interrupt */
 140 }
 141
 142 static void tlb_remove_table_sync_one(void)
 143 {
 144         /*
 145          * This isn't an RCU grace period and hence the page-tables cannot be
 146          * assumed to be actually RCU-freed.
 147          *
 148          * It is however sufficient for software page-table walkers that rely on
 149          * IRQ disabling.
 150          */
 151         smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
 152 }
 153
 154 static void tlb_remove_table_rcu(struct rcu_head *head)
 155 {
 156         __tlb_remove_table_free(container_of(head, struct mmu_table_batch, rcu));
 157 }
 158
 159 static void tlb_remove_table_free(struct mmu_table_batch *batch)
 160 {
 161         call_rcu(&batch->rcu, tlb_remove_table_rcu);
 162 }
 163
 164 #else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */
 165
 166 static void tlb_remove_table_sync_one(void) { }
 167
 168 static void tlb_remove_table_free(struct mmu_table_batch *batch)
 169 {
 170         __tlb_remove_table_free(batch);
 171 }
 172
 173 #endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
 174
 175 /*
 176  * If we want tlb_remove_table() to imply TLB invalidates.
 177  */
 178 static inline void tlb_table_invalidate(struct mmu_gather *tlb)
 179 {
 180         if (tlb_needs_table_invalidate()) {
 181                 /*
 182                  * Invalidate page-table caches used by hardware walkers. Then
 183                  * we still need to RCU-sched wait while freeing the pages
 184                  * because software walkers can still be in-flight.
 185                  */
 186                 tlb_flush_mmu_tlbonly(tlb);
 187         }
 188 }
 189
 190 static void tlb_remove_table_one(void *table)
 191 {
 192         tlb_remove_table_sync_one();
 193         __tlb_remove_table(table);
 194 }
 195
 196 static void tlb_table_flush(struct mmu_gather *tlb)
 197 {
 198         struct mmu_table_batch **batch = &tlb->batch;
 199
 200         if (*batch) {
 201                 tlb_table_invalidate(tlb);
 202                 tlb_remove_table_free(*batch);
 203                 *batch = NULL;
 204         }
 205 }
 206
 207 void tlb_remove_table(struct mmu_gather *tlb, void *table)
 208 {
 209         struct mmu_table_batch **batch = &tlb->batch;
 210
 211         if (*batch == NULL) {
 212                 *batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
 213                 if (*batch == NULL) {
 214                         tlb_table_invalidate(tlb);
 215                         tlb_remove_table_one(table);
 216                         return;
 217                 }
 218                 (*batch)->nr = 0;
 219         }
 220
 221         (*batch)->tables[(*batch)->nr++] = table;
 222         if ((*batch)->nr == MAX_TABLE_BATCH)
 223                 tlb_table_flush(tlb);
 224 }
 225
 226 static inline void tlb_table_init(struct mmu_gather *tlb)
 227 {
 228         tlb->batch = NULL;
 229 }
 230
 231 #else /* !CONFIG_MMU_GATHER_TABLE_FREE */
 232
 233 static inline void tlb_table_flush(struct mmu_gather *tlb) { }
 234 static inline void tlb_table_init(struct mmu_gather *tlb) { }
 235
 236 #endif /* CONFIG_MMU_GATHER_TABLE_FREE */
 237
 238 static void tlb_flush_mmu_free(struct mmu_gather *tlb)
 239 {
 240         tlb_table_flush(tlb);
 241 #ifndef CONFIG_MMU_GATHER_NO_GATHER
 242         tlb_batch_pages_flush(tlb);
 243 #endif
 244 }
 245
 246 void tlb_flush_mmu(struct mmu_gather *tlb)
 247 {
 248         tlb_flush_mmu_tlbonly(tlb);
 249         tlb_flush_mmu_free(tlb);
 250 }
 251
 252 /**
 253  * tlb_gather_mmu - initialize an mmu_gather structure for page-table tear-down
 254  * @tlb: the mmu_gather structure to initialize
 255  * @mm: the mm_struct of the target address space
 256  * @start: start of the region that will be removed from the page-table
 257  * @end: end of the region that will be removed from the page-table
 258  *
 259  * Called to initialize an (on-stack) mmu_gather structure for page-table
 260  * tear-down from @mm. The @start and @end are set to 0 and -1
 261  * respectively when @mm is without users and we're going to destroy
 262  * the full address space (exit/execve).
 263  */
 264 void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
 265                         unsigned long start, unsigned long end)
 266 {
 267         tlb->mm = mm;
 268
 269         /* Is it from 0 to ~0? */
 270         tlb->fullmm     = !(start | (end+1));
 271
 272 #ifndef CONFIG_MMU_GATHER_NO_GATHER
 273         tlb->need_flush_all = 0;
 274         tlb->local.next = NULL;
 275         tlb->local.nr   = 0;
 276         tlb->local.max  = ARRAY_SIZE(tlb->__pages);
 277         tlb->active     = &tlb->local;
 278         tlb->batch_count = 0;
 279 #endif
 280
 281         tlb_table_init(tlb);
 282 #ifdef CONFIG_MMU_GATHER_PAGE_SIZE
 283         tlb->page_size = 0;
 284 #endif
 285
 286         __tlb_reset_range(tlb);
 287         inc_tlb_flush_pending(tlb->mm);
 288 }
 289
 290 /**
 291  * tlb_finish_mmu - finish an mmu_gather structure
 292  * @tlb: the mmu_gather structure to finish
 293  * @start: start of the region that will be removed from the page-table
 294  * @end: end of the region that will be removed from the page-table
 295  *
 296  * Called at the end of the shootdown operation to free up any resources that
 297  * were required.
 298  */
 299 void tlb_finish_mmu(struct mmu_gather *tlb,
 300                 unsigned long start, unsigned long end)
 301 {
 302         /*
 303          * If there are parallel threads are doing PTE changes on same range
 304          * under non-exclusive lock (e.g., mmap_sem read-side) but defer TLB
 305          * flush by batching, one thread may end up seeing inconsistent PTEs
 306          * and result in having stale TLB entries.  So flush TLB forcefully
 307          * if we detect parallel PTE batching threads.
 308          *
 309          * However, some syscalls, e.g. munmap(), may free page tables, this
 310          * needs force flush everything in the given range. Otherwise this
 311          * may result in having stale TLB entries for some architectures,
 312          * e.g. aarch64, that could specify flush what level TLB.
 313          */
 314         if (mm_tlb_flush_nested(tlb->mm)) {
 315                 /*
 316                  * The aarch64 yields better performance with fullmm by
 317                  * avoiding multiple CPUs spamming TLBI messages at the
 318                  * same time.
 319                  *
 320                  * On x86 non-fullmm doesn't yield significant difference
 321                  * against fullmm.
 322                  */
 323                 tlb->fullmm = 1;
 324                 __tlb_reset_range(tlb);
 325                 tlb->freed_tables = 1;
 326         }
 327
 328         tlb_flush_mmu(tlb);
 329
 330 #ifndef CONFIG_MMU_GATHER_NO_GATHER
 331         tlb_batch_list_free(tlb);
 332 #endif
 333         dec_tlb_flush_pending(tlb->mm);
 334 }