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![Peter Zijlstra](/assets/img/avatar_default.png)
As described in the comment, the correct order for freeing pages is: 1) unhook page 2) TLB invalidate page 3) free page This order equally applies to page directories. Currently there are two correct options: - use tlb_remove_page(), when all page directores are full pages and there are no futher contraints placed by things like software walkers (HAVE_FAST_GUP). - use MMU_GATHER_RCU_TABLE_FREE and tlb_remove_table() when the architecture does not do IPI based TLB invalidate and has HAVE_FAST_GUP (or software TLB fill). This however leaves architectures that don't have page based directories but don't need RCU in a bind. For those, provide MMU_GATHER_TABLE_FREE, which provides the independent batching for directories without the additional RCU freeing. Link: http://lkml.kernel.org/r/20200116064531.483522-10-aneesh.kumar@linux.ibm.com Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
334 lines
8.4 KiB
C
334 lines
8.4 KiB
C
#include <linux/gfp.h>
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#include <linux/highmem.h>
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#include <linux/kernel.h>
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#include <linux/mmdebug.h>
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#include <linux/mm_types.h>
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#include <linux/pagemap.h>
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#include <linux/rcupdate.h>
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#include <linux/smp.h>
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#include <linux/swap.h>
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#include <asm/pgalloc.h>
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#include <asm/tlb.h>
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#ifndef CONFIG_MMU_GATHER_NO_GATHER
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static bool tlb_next_batch(struct mmu_gather *tlb)
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{
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struct mmu_gather_batch *batch;
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batch = tlb->active;
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if (batch->next) {
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tlb->active = batch->next;
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return true;
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}
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if (tlb->batch_count == MAX_GATHER_BATCH_COUNT)
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return false;
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batch = (void *)__get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
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if (!batch)
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return false;
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tlb->batch_count++;
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batch->next = NULL;
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batch->nr = 0;
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batch->max = MAX_GATHER_BATCH;
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tlb->active->next = batch;
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tlb->active = batch;
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return true;
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}
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static void tlb_batch_pages_flush(struct mmu_gather *tlb)
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{
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struct mmu_gather_batch *batch;
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for (batch = &tlb->local; batch && batch->nr; batch = batch->next) {
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free_pages_and_swap_cache(batch->pages, batch->nr);
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batch->nr = 0;
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}
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tlb->active = &tlb->local;
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}
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static void tlb_batch_list_free(struct mmu_gather *tlb)
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{
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struct mmu_gather_batch *batch, *next;
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for (batch = tlb->local.next; batch; batch = next) {
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next = batch->next;
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free_pages((unsigned long)batch, 0);
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}
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tlb->local.next = NULL;
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}
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bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_size)
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{
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struct mmu_gather_batch *batch;
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VM_BUG_ON(!tlb->end);
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#ifdef CONFIG_MMU_GATHER_PAGE_SIZE
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VM_WARN_ON(tlb->page_size != page_size);
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#endif
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batch = tlb->active;
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/*
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* Add the page and check if we are full. If so
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* force a flush.
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*/
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batch->pages[batch->nr++] = page;
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if (batch->nr == batch->max) {
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if (!tlb_next_batch(tlb))
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return true;
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batch = tlb->active;
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}
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VM_BUG_ON_PAGE(batch->nr > batch->max, page);
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return false;
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}
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#endif /* MMU_GATHER_NO_GATHER */
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#ifdef CONFIG_MMU_GATHER_TABLE_FREE
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static void __tlb_remove_table_free(struct mmu_table_batch *batch)
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{
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int i;
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for (i = 0; i < batch->nr; i++)
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__tlb_remove_table(batch->tables[i]);
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free_page((unsigned long)batch);
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}
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#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
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/*
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* Semi RCU freeing of the page directories.
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*
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* This is needed by some architectures to implement software pagetable walkers.
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*
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* gup_fast() and other software pagetable walkers do a lockless page-table
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* walk and therefore needs some synchronization with the freeing of the page
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* directories. The chosen means to accomplish that is by disabling IRQs over
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* the walk.
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*
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* Architectures that use IPIs to flush TLBs will then automagically DTRT,
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* since we unlink the page, flush TLBs, free the page. Since the disabling of
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* IRQs delays the completion of the TLB flush we can never observe an already
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* freed page.
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*
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* Architectures that do not have this (PPC) need to delay the freeing by some
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* other means, this is that means.
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*
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* What we do is batch the freed directory pages (tables) and RCU free them.
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* We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
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* holds off grace periods.
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*
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* However, in order to batch these pages we need to allocate storage, this
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* allocation is deep inside the MM code and can thus easily fail on memory
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* pressure. To guarantee progress we fall back to single table freeing, see
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* the implementation of tlb_remove_table_one().
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*
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*/
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static void tlb_remove_table_smp_sync(void *arg)
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{
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/* Simply deliver the interrupt */
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}
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static void tlb_remove_table_sync_one(void)
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{
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/*
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* This isn't an RCU grace period and hence the page-tables cannot be
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* assumed to be actually RCU-freed.
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*
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* It is however sufficient for software page-table walkers that rely on
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* IRQ disabling.
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*/
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smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
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}
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static void tlb_remove_table_rcu(struct rcu_head *head)
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{
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__tlb_remove_table_free(container_of(head, struct mmu_table_batch, rcu));
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}
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static void tlb_remove_table_free(struct mmu_table_batch *batch)
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{
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call_rcu(&batch->rcu, tlb_remove_table_rcu);
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}
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#else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */
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static void tlb_remove_table_sync_one(void) { }
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static void tlb_remove_table_free(struct mmu_table_batch *batch)
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{
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__tlb_remove_table_free(batch);
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}
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#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
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/*
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* If we want tlb_remove_table() to imply TLB invalidates.
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*/
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static inline void tlb_table_invalidate(struct mmu_gather *tlb)
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{
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if (tlb_needs_table_invalidate()) {
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/*
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* Invalidate page-table caches used by hardware walkers. Then
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* we still need to RCU-sched wait while freeing the pages
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* because software walkers can still be in-flight.
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*/
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tlb_flush_mmu_tlbonly(tlb);
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}
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}
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static void tlb_remove_table_one(void *table)
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{
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tlb_remove_table_sync_one();
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__tlb_remove_table(table);
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}
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static void tlb_table_flush(struct mmu_gather *tlb)
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{
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struct mmu_table_batch **batch = &tlb->batch;
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if (*batch) {
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tlb_table_invalidate(tlb);
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tlb_remove_table_free(*batch);
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*batch = NULL;
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}
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}
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void tlb_remove_table(struct mmu_gather *tlb, void *table)
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{
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struct mmu_table_batch **batch = &tlb->batch;
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if (*batch == NULL) {
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*batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
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if (*batch == NULL) {
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tlb_table_invalidate(tlb);
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tlb_remove_table_one(table);
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return;
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}
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(*batch)->nr = 0;
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}
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(*batch)->tables[(*batch)->nr++] = table;
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if ((*batch)->nr == MAX_TABLE_BATCH)
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tlb_table_flush(tlb);
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}
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static inline void tlb_table_init(struct mmu_gather *tlb)
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{
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tlb->batch = NULL;
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}
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#else /* !CONFIG_MMU_GATHER_TABLE_FREE */
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static inline void tlb_table_flush(struct mmu_gather *tlb) { }
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static inline void tlb_table_init(struct mmu_gather *tlb) { }
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#endif /* CONFIG_MMU_GATHER_TABLE_FREE */
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static void tlb_flush_mmu_free(struct mmu_gather *tlb)
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{
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tlb_table_flush(tlb);
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#ifndef CONFIG_MMU_GATHER_NO_GATHER
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tlb_batch_pages_flush(tlb);
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#endif
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}
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void tlb_flush_mmu(struct mmu_gather *tlb)
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{
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tlb_flush_mmu_tlbonly(tlb);
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tlb_flush_mmu_free(tlb);
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}
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/**
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* tlb_gather_mmu - initialize an mmu_gather structure for page-table tear-down
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* @tlb: the mmu_gather structure to initialize
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* @mm: the mm_struct of the target address space
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* @start: start of the region that will be removed from the page-table
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* @end: end of the region that will be removed from the page-table
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*
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* Called to initialize an (on-stack) mmu_gather structure for page-table
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* tear-down from @mm. The @start and @end are set to 0 and -1
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* respectively when @mm is without users and we're going to destroy
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* the full address space (exit/execve).
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*/
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void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
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unsigned long start, unsigned long end)
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{
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tlb->mm = mm;
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/* Is it from 0 to ~0? */
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tlb->fullmm = !(start | (end+1));
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#ifndef CONFIG_MMU_GATHER_NO_GATHER
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tlb->need_flush_all = 0;
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tlb->local.next = NULL;
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tlb->local.nr = 0;
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tlb->local.max = ARRAY_SIZE(tlb->__pages);
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tlb->active = &tlb->local;
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tlb->batch_count = 0;
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#endif
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tlb_table_init(tlb);
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#ifdef CONFIG_MMU_GATHER_PAGE_SIZE
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tlb->page_size = 0;
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#endif
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__tlb_reset_range(tlb);
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inc_tlb_flush_pending(tlb->mm);
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}
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/**
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* tlb_finish_mmu - finish an mmu_gather structure
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* @tlb: the mmu_gather structure to finish
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* @start: start of the region that will be removed from the page-table
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* @end: end of the region that will be removed from the page-table
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*
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* Called at the end of the shootdown operation to free up any resources that
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* were required.
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*/
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void tlb_finish_mmu(struct mmu_gather *tlb,
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unsigned long start, unsigned long end)
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{
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/*
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* If there are parallel threads are doing PTE changes on same range
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* under non-exclusive lock (e.g., mmap_sem read-side) but defer TLB
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* flush by batching, one thread may end up seeing inconsistent PTEs
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* and result in having stale TLB entries. So flush TLB forcefully
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* if we detect parallel PTE batching threads.
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*
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* However, some syscalls, e.g. munmap(), may free page tables, this
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* needs force flush everything in the given range. Otherwise this
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* may result in having stale TLB entries for some architectures,
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* e.g. aarch64, that could specify flush what level TLB.
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*/
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if (mm_tlb_flush_nested(tlb->mm)) {
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/*
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* The aarch64 yields better performance with fullmm by
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* avoiding multiple CPUs spamming TLBI messages at the
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* same time.
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*
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* On x86 non-fullmm doesn't yield significant difference
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* against fullmm.
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*/
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tlb->fullmm = 1;
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__tlb_reset_range(tlb);
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tlb->freed_tables = 1;
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}
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tlb_flush_mmu(tlb);
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#ifndef CONFIG_MMU_GATHER_NO_GATHER
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tlb_batch_list_free(tlb);
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#endif
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dec_tlb_flush_pending(tlb->mm);
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}
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