powerpc/pseries: Introduce rwlock to gatekeep DTLB usage

Since we would be introducing a new user of the DTL buffer in a subsequent patch, we need a way to gatekeep use of the DTL buffer. The current debugfs interface for DTL allows registering and opening cpu-specific DTL buffers. Cpu specific files are exposed under debugfs 'powerpc/dtl/' node, and changing 'dtl_event_mask' in the same directory enables controlling the event mask used when registering DTL buffer for a particular cpu. Subsequently, we will be introducing a user of the DTL buffers that registers access to the DTL buffers across all cpus with the same event mask. To ensure these two users do not step on each other, we introduce a rwlock to gatekeep DTL buffer access. This fits the requirement of the current debugfs interface wanting to allow multiple independent cpu-specific users (read lock), and the subsequent user wanting exclusive access (write lock). Suggested-by: Michael Ellerman <[email protected]> Signed-off-by: Naveen N. Rao <[email protected]> Signed-off-by: Michael Ellerman <[email protected]>
linuxppc · Jul 4, 2019 · 06220d7 · 06220d7
1 parent 1c85a2a
commit 06220d7
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Showing 3 changed files with 16 additions and 1 deletion.
diff --git a/arch/powerpc/include/asm/lppaca.h b/arch/powerpc/include/asm/lppaca.h
@@ -32,6 +32,7 @@
  */
 #include <linux/cache.h>
 #include <linux/threads.h>
+#include <linux/spinlock_types.h>
 #include <asm/types.h>
 #include <asm/mmu.h>
 #include <asm/firmware.h>
@@ -166,6 +167,7 @@ struct dtl_entry {
 #define DTL_LOG_ALL		(DTL_LOG_CEDE | DTL_LOG_PREEMPT | DTL_LOG_FAULT)
 
 extern struct kmem_cache *dtl_cache;
+extern rwlock_t dtl_access_lock;
 
 /*
  * When CONFIG_VIRT_CPU_ACCOUNTING_NATIVE = y, the cpu accounting code controls

diff --git a/arch/powerpc/platforms/pseries/dtl.c b/arch/powerpc/platforms/pseries/dtl.c
@@ -193,11 +193,16 @@ static int dtl_enable(struct dtl *dtl)
 	if (dtl->buf)
 		return -EBUSY;
 
+	/* ensure there are no other conflicting dtl users */
+	if (!read_trylock(&dtl_access_lock))
+		return -EBUSY;
+
 	n_entries = dtl_buf_entries;
 	buf = kmem_cache_alloc_node(dtl_cache, GFP_KERNEL, cpu_to_node(dtl->cpu));
 	if (!buf) {
 		printk(KERN_WARNING "%s: buffer alloc failed for cpu %d\n",
 				__func__, dtl->cpu);
+		read_unlock(&dtl_access_lock);
 		return -ENOMEM;
 	}
 
@@ -214,8 +219,11 @@ static int dtl_enable(struct dtl *dtl)
 	}
 	spin_unlock(&dtl->lock);
 
-	if (rc)
+	if (rc) {
+		read_unlock(&dtl_access_lock);
 		kmem_cache_free(dtl_cache, buf);
+	}
+
 	return rc;
 }
 
@@ -227,6 +235,7 @@ static void dtl_disable(struct dtl *dtl)
 	dtl->buf = NULL;
 	dtl->buf_entries = 0;
 	spin_unlock(&dtl->lock);
+	read_unlock(&dtl_access_lock);
 }
 
 /* file interface */

diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
@@ -113,6 +113,10 @@ void register_dtl_buffer(int cpu)
 	}
 }
 
+#ifdef CONFIG_PPC_SPLPAR
+DEFINE_RWLOCK(dtl_access_lock);
+#endif /* CONFIG_PPC_SPLPAR */
+
 void vpa_init(int cpu)
 {
 	int hwcpu = get_hard_smp_processor_id(cpu);