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authorPeter Zijlstra <peterz@infradead.org>2020-02-03 17:37:11 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-02-04 03:05:26 +0000
commit0d6e24d430ef23280d8dea0ba1faeefc66c26a57 (patch)
tree6fb47b4bee252781c30105392a143e9a9a688903 /mm/mmu_gather.c
parent580a586c409ab3040b7284a19cd9e281692c40c7 (diff)
asm-generic/tlb: provide MMU_GATHER_TABLE_FREE
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>
Diffstat (limited to 'mm/mmu_gather.c')
-rw-r--r--mm/mmu_gather.c120
1 files changed, 88 insertions, 32 deletions
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index a28c74328085..a3538cb2bcbe 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -91,56 +91,106 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_
#endif /* MMU_GATHER_NO_GATHER */
-#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
+#ifdef CONFIG_MMU_GATHER_TABLE_FREE
-/*
- * See the comment near struct mmu_table_batch.
- */
+static void __tlb_remove_table_free(struct mmu_table_batch *batch)
+{
+ int i;
+
+ for (i = 0; i < batch->nr; i++)
+ __tlb_remove_table(batch->tables[i]);
+
+ free_page((unsigned long)batch);
+}
+
+#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
/*
- * If we want tlb_remove_table() to imply TLB invalidates.
+ * Semi RCU freeing of the page directories.
+ *
+ * This is needed by some architectures to implement software pagetable walkers.
+ *
+ * gup_fast() and other software pagetable walkers do a lockless page-table
+ * walk and therefore needs some synchronization with the freeing of the page
+ * directories. The chosen means to accomplish that is by disabling IRQs over
+ * the walk.
+ *
+ * Architectures that use IPIs to flush TLBs will then automagically DTRT,
+ * since we unlink the page, flush TLBs, free the page. Since the disabling of
+ * IRQs delays the completion of the TLB flush we can never observe an already
+ * freed page.
+ *
+ * Architectures that do not have this (PPC) need to delay the freeing by some
+ * other means, this is that means.
+ *
+ * What we do is batch the freed directory pages (tables) and RCU free them.
+ * We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
+ * holds off grace periods.
+ *
+ * However, in order to batch these pages we need to allocate storage, this
+ * allocation is deep inside the MM code and can thus easily fail on memory
+ * pressure. To guarantee progress we fall back to single table freeing, see
+ * the implementation of tlb_remove_table_one().
+ *
*/
-static inline void tlb_table_invalidate(struct mmu_gather *tlb)
-{
- if (tlb_needs_table_invalidate()) {
- /*
- * Invalidate page-table caches used by hardware walkers. Then
- * we still need to RCU-sched wait while freeing the pages
- * because software walkers can still be in-flight.
- */
- tlb_flush_mmu_tlbonly(tlb);
- }
-}
static void tlb_remove_table_smp_sync(void *arg)
{
/* Simply deliver the interrupt */
}
-static void tlb_remove_table_one(void *table)
+static void tlb_remove_table_sync_one(void)
{
/*
* This isn't an RCU grace period and hence the page-tables cannot be
* assumed to be actually RCU-freed.
*
* It is however sufficient for software page-table walkers that rely on
- * IRQ disabling. See the comment near struct mmu_table_batch.
+ * IRQ disabling.
*/
smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
- __tlb_remove_table(table);
}
static void tlb_remove_table_rcu(struct rcu_head *head)
{
- struct mmu_table_batch *batch;
- int i;
+ __tlb_remove_table_free(container_of(head, struct mmu_table_batch, rcu));
+}
- batch = container_of(head, struct mmu_table_batch, rcu);
+static void tlb_remove_table_free(struct mmu_table_batch *batch)
+{
+ call_rcu(&batch->rcu, tlb_remove_table_rcu);
+}
- for (i = 0; i < batch->nr; i++)
- __tlb_remove_table(batch->tables[i]);
+#else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */
- free_page((unsigned long)batch);
+static void tlb_remove_table_sync_one(void) { }
+
+static void tlb_remove_table_free(struct mmu_table_batch *batch)
+{
+ __tlb_remove_table_free(batch);
+}
+
+#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
+
+/*
+ * If we want tlb_remove_table() to imply TLB invalidates.
+ */
+static inline void tlb_table_invalidate(struct mmu_gather *tlb)
+{
+ if (tlb_needs_table_invalidate()) {
+ /*
+ * Invalidate page-table caches used by hardware walkers. Then
+ * we still need to RCU-sched wait while freeing the pages
+ * because software walkers can still be in-flight.
+ */
+ tlb_flush_mmu_tlbonly(tlb);
+ }
+}
+
+static void tlb_remove_table_one(void *table)
+{
+ tlb_remove_table_sync_one();
+ __tlb_remove_table(table);
}
static void tlb_table_flush(struct mmu_gather *tlb)
@@ -149,7 +199,7 @@ static void tlb_table_flush(struct mmu_gather *tlb)
if (*batch) {
tlb_table_invalidate(tlb);
- call_rcu(&(*batch)->rcu, tlb_remove_table_rcu);
+ tlb_remove_table_free(*batch);
*batch = NULL;
}
}
@@ -173,13 +223,21 @@ void tlb_remove_table(struct mmu_gather *tlb, void *table)
tlb_table_flush(tlb);
}
-#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
+static inline void tlb_table_init(struct mmu_gather *tlb)
+{
+ tlb->batch = NULL;
+}
+
+#else /* !CONFIG_MMU_GATHER_TABLE_FREE */
+
+static inline void tlb_table_flush(struct mmu_gather *tlb) { }
+static inline void tlb_table_init(struct mmu_gather *tlb) { }
+
+#endif /* CONFIG_MMU_GATHER_TABLE_FREE */
static void tlb_flush_mmu_free(struct mmu_gather *tlb)
{
-#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
tlb_table_flush(tlb);
-#endif
#ifndef CONFIG_MMU_GATHER_NO_GATHER
tlb_batch_pages_flush(tlb);
#endif
@@ -220,9 +278,7 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
tlb->batch_count = 0;
#endif
-#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
- tlb->batch = NULL;
-#endif
+ tlb_table_init(tlb);
#ifdef CONFIG_MMU_GATHER_PAGE_SIZE
tlb->page_size = 0;
#endif