ramoops: Split ftrace buffer space into per-CPU zones

If the RAMOOPS_FLAG_FTRACE_PER_CPU flag is passed to ramoops pdata, split
the ftrace space into multiple zones depending on the number of CPUs.

This speeds up the performance of function tracing by about 280% in my
tests as we avoid the locking. The trade off being lesser space available
per CPU. Let the ramoops user decide which option they want based on pdata
flag.
Signed-off-by: Joel Fernandes <joelaf@google.com>
[kees: added max_ftrace_cnt to track size, added DT logic and docs]
Signed-off-by: Kees Cook <keescook@chromium.org>

Documentation/devicetree/bindings/reserved-memory/ramoops.txt

@@ -46,3 +46,6 @@ Optional properties:
   (defaults to buffered mappings)
 
 - no-dump-oops: if present, only dump panics (defaults to panics and oops)
+
+- flags: if present, pass ramoops behavioral flags (defaults to 0,
+  see include/linux/pstore_ram.h RAMOOPS_FLAG_* for flag values).

fs/pstore/ram.c

@@ -87,7 +87,7 @@ MODULE_PARM_DESC(ramoops_ecc,
 struct ramoops_context {
 	struct persistent_ram_zone **przs;
 	struct persistent_ram_zone *cprz;
-	struct persistent_ram_zone *fprz;
+	struct persistent_ram_zone **fprzs;
 	struct persistent_ram_zone *mprz;
 	phys_addr_t phys_addr;
 	unsigned long size;
@@ -97,12 +97,14 @@ struct ramoops_context {
 	size_t ftrace_size;
 	size_t pmsg_size;
 	int dump_oops;
+	u32 flags;
 	struct persistent_ram_ecc_info ecc_info;
 	unsigned int max_dump_cnt;
 	unsigned int dump_write_cnt;
 	/* _read_cnt need clear on ramoops_pstore_open */
 	unsigned int dump_read_cnt;
 	unsigned int console_read_cnt;
+	unsigned int max_ftrace_cnt;
 	unsigned int ftrace_read_cnt;
 	unsigned int pmsg_read_cnt;
 	struct pstore_info pstore;
@@ -219,9 +221,17 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
 	if (!prz_ok(prz))
 		prz = ramoops_get_next_prz(&cxt->cprz, &cxt->console_read_cnt,
 					   1, id, type, PSTORE_TYPE_CONSOLE, 0);
-	if (!prz_ok(prz))
-		prz = ramoops_get_next_prz(&cxt->fprz, &cxt->ftrace_read_cnt,
-					   1, id, type, PSTORE_TYPE_FTRACE, 0);
+	if (!prz_ok(prz)) {
+		while (cxt->ftrace_read_cnt < cxt->max_ftrace_cnt && !prz) {
+			prz = ramoops_get_next_prz(cxt->fprzs,
+					&cxt->ftrace_read_cnt,
+					cxt->max_ftrace_cnt, id, type,
+					PSTORE_TYPE_FTRACE, 0);
+			if (!prz_ok(prz))
+				continue;
+		}
+	}
+
 	if (!prz_ok(prz))
 		prz = ramoops_get_next_prz(&cxt->mprz, &cxt->pmsg_read_cnt,
 					   1, id, type, PSTORE_TYPE_PMSG, 0);
@@ -283,9 +293,19 @@ static int notrace ramoops_pstore_write_buf(enum pstore_type_id type,
 		persistent_ram_write(cxt->cprz, buf, size);
 		return 0;
 	} else if (type == PSTORE_TYPE_FTRACE) {
-		if (!cxt->fprz)
+		int zonenum;
+
+		if (!cxt->fprzs)
 			return -ENOMEM;
-		persistent_ram_write(cxt->fprz, buf, size);
+		/*
+		 * Choose zone by if we're using per-cpu buffers.
+		 */
+		if (cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU)
+			zonenum = smp_processor_id();
+		else
+			zonenum = 0;
+
+		persistent_ram_write(cxt->fprzs[zonenum], buf, size);
 		return 0;
 	} else if (type == PSTORE_TYPE_PMSG) {
 		pr_warn_ratelimited("PMSG shouldn't call %s\n", __func__);
@@ -363,7 +383,9 @@ static int ramoops_pstore_erase(enum pstore_type_id type, u64 id, int count,
 		prz = cxt->cprz;
 		break;
 	case PSTORE_TYPE_FTRACE:
-		prz = cxt->fprz;
+		if (id >= cxt->max_ftrace_cnt)
+			return -EINVAL;
+		prz = cxt->fprzs[id];
 		break;
 	case PSTORE_TYPE_PMSG:
 		prz = cxt->mprz;
@@ -394,14 +416,22 @@ static void ramoops_free_przs(struct ramoops_context *cxt)
 {
 	int i;
 
-	if (!cxt->przs)
-		return;
+	/* Free dump PRZs */
+	if (cxt->przs) {
+		for (i = 0; i < cxt->max_dump_cnt; i++)
+			persistent_ram_free(cxt->przs[i]);
 
-	for (i = 0; i < cxt->max_dump_cnt; i++)
-		persistent_ram_free(cxt->przs[i]);
+		kfree(cxt->przs);
+		cxt->max_dump_cnt = 0;
+	}
 
-	kfree(cxt->przs);
-	cxt->max_dump_cnt = 0;
+	/* Free ftrace PRZs */
+	if (cxt->fprzs) {
+		for (i = 0; i < cxt->max_ftrace_cnt; i++)
+			persistent_ram_free(cxt->fprzs[i]);
+		kfree(cxt->fprzs);
+		cxt->max_ftrace_cnt = 0;
+	}
 }
 
 static int ramoops_init_przs(struct device *dev, struct ramoops_context *cxt,
@@ -567,6 +597,7 @@ static int ramoops_parse_dt(struct platform_device *pdev,
 	parse_size("ftrace-size", pdata->ftrace_size);
 	parse_size("pmsg-size", pdata->pmsg_size);
 	parse_size("ecc-size", pdata->ecc_info.ecc_size);
+	parse_size("flags", pdata->flags);
 
 #undef parse_size
 
@@ -624,6 +655,7 @@ static int ramoops_probe(struct platform_device *pdev)
 	cxt->ftrace_size = pdata->ftrace_size;
 	cxt->pmsg_size = pdata->pmsg_size;
 	cxt->dump_oops = pdata->dump_oops;
+	cxt->flags = pdata->flags;
 	cxt->ecc_info = pdata->ecc_info;
 
 	paddr = cxt->phys_addr;
@@ -640,8 +672,14 @@ static int ramoops_probe(struct platform_device *pdev)
 	if (err)
 		goto fail_init_cprz;
 
-	err = ramoops_init_prz(dev, cxt, &cxt->fprz, &paddr, cxt->ftrace_size,
-			       LINUX_VERSION_CODE);
+	cxt->max_ftrace_cnt = (cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU)
+				? nr_cpu_ids
+				: 1;
+	err = ramoops_init_przs(dev, cxt, &cxt->fprzs, &paddr, cxt->ftrace_size,
+				-1, &cxt->max_ftrace_cnt,
+				LINUX_VERSION_CODE,
+				(cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU)
+					? PRZ_FLAG_NO_LOCK : 0);
 	if (err)
 		goto fail_init_fprz;
 
@@ -705,7 +743,6 @@ static int ramoops_probe(struct platform_device *pdev)
 	cxt->pstore.bufsize = 0;
 	persistent_ram_free(cxt->mprz);
 fail_init_mprz:
-	persistent_ram_free(cxt->fprz);
 fail_init_fprz:
 	persistent_ram_free(cxt->cprz);
 fail_init_cprz:
@@ -724,7 +761,6 @@ static int ramoops_remove(struct platform_device *pdev)
 	cxt->pstore.bufsize = 0;
 
 	persistent_ram_free(cxt->mprz);
-	persistent_ram_free(cxt->fprz);
 	persistent_ram_free(cxt->cprz);
 	ramoops_free_przs(cxt);
 
@@ -766,6 +802,8 @@ static void ramoops_register_dummy(void)
 	dummy_data->ftrace_size = ramoops_ftrace_size;
 	dummy_data->pmsg_size = ramoops_pmsg_size;
 	dummy_data->dump_oops = dump_oops;
+	dummy_data->flags = RAMOOPS_FLAG_FTRACE_PER_CPU;
+
 	/*
 	 * For backwards compatibility ramoops.ecc=1 means 16 bytes ECC
 	 * (using 1 byte for ECC isn't much of use anyway).

include/linux/pstore_ram.h

@@ -86,6 +86,8 @@ ssize_t persistent_ram_ecc_string(struct persistent_ram_zone *prz,
  * @mem_address	physical memory address to contain ramoops
  */
 
+#define RAMOOPS_FLAG_FTRACE_PER_CPU	BIT(0)
+
 struct ramoops_platform_data {
 	unsigned long	mem_size;
 	phys_addr_t	mem_address;
@@ -95,6 +97,7 @@ struct ramoops_platform_data {
 	unsigned long	ftrace_size;
 	unsigned long	pmsg_size;
 	int		dump_oops;
+	u32		flags;
 	struct persistent_ram_ecc_info ecc_info;
 };