[PATCH V2 1/1] powerpc/perf/hv-gpci: Increase request buffer size

[Sukadev Bhattiprolu]

>From f1afe08fbc9797ff63adf03efe564a807a37cfe6 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
Date: Tue, 9 Feb 2016 02:47:45 -0500
Subject: [PATCH V2 1/1] powerpc/perf/hv-gpci: Increase request buffer size

The GPCI hcall allows for a 4K buffer but we limit the buffer to 1K.
The problem with a 1K buffer is if a request results in returning
more values than can be accomodated in the 1K buffer the request will
fail.

The buffer we are using is currently allocated on the stack and hence
limited in size. Instead use a per-CPU 4K buffer like we do with 24x7
counters (hv-24x7.c).

While here, rename the macro GPCI_MAX_DATA_BYTES to HGPCI_MAX_DATA_BYTES
for consistency with 24x7 counters.

Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
---
Changelog[v2]:
	- [Michael Ellerman] Specify the exact size of buffer in
	  the GPCI request rather than use an array elment of 1.
---
 arch/powerpc/perf/hv-gpci.c | 43 +++++++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
index 856fe6e..7aa3723 100644
--- a/arch/powerpc/perf/hv-gpci.c
+++ b/arch/powerpc/perf/hv-gpci.c
@@ -127,8 +127,16 @@ static const struct attribute_group *attr_groups[] = {
 	NULL,
 };
 
-#define GPCI_MAX_DATA_BYTES \
-	(1024 - sizeof(struct hv_get_perf_counter_info_params))
+#define HGPCI_REQ_BUFFER_SIZE	4096
+#define HGPCI_MAX_DATA_BYTES \
+	(HGPCI_REQ_BUFFER_SIZE - sizeof(struct hv_get_perf_counter_info_params))
+
+DEFINE_PER_CPU(char, hv_gpci_reqb[HGPCI_REQ_BUFFER_SIZE]) __aligned(sizeof(uint64_t));
+
+struct hv_gpci_request_buffer {
+	struct hv_get_perf_counter_info_params params;
+	uint8_t bytes[HGPCI_MAX_DATA_BYTES];
+} __packed;
 
 static unsigned long single_gpci_request(u32 req, u32 starting_index,
 		u16 secondary_index, u8 version_in, u32 offset, u8 length,
@@ -137,24 +145,21 @@ static unsigned long single_gpci_request(u32 req, u32 starting_index,
 	unsigned long ret;
 	size_t i;
 	u64 count;
+	struct hv_gpci_request_buffer *arg;
+
+	arg = (void *)get_cpu_var(hv_gpci_reqb);
+	memset(arg, 0, HGPCI_REQ_BUFFER_SIZE);
 
-	struct {
-		struct hv_get_perf_counter_info_params params;
-		uint8_t bytes[GPCI_MAX_DATA_BYTES];
-	} __packed __aligned(sizeof(uint64_t)) arg = {
-		.params = {
-			.counter_request = cpu_to_be32(req),
-			.starting_index = cpu_to_be32(starting_index),
-			.secondary_index = cpu_to_be16(secondary_index),
-			.counter_info_version_in = version_in,
-		}
-	};
+	arg->params.counter_request = cpu_to_be32(req);
+	arg->params.starting_index = cpu_to_be32(starting_index);
+	arg->params.secondary_index = cpu_to_be16(secondary_index);
+	arg->params.counter_info_version_in = version_in;
 
 	ret = plpar_hcall_norets(H_GET_PERF_COUNTER_INFO,
-			virt_to_phys(&arg), sizeof(arg));
+			virt_to_phys(arg), HGPCI_REQ_BUFFER_SIZE);
 	if (ret) {
 		pr_devel("hcall failed: 0x%lx\n", ret);
-		return ret;
+		goto out;
 	}
 
 	/*
@@ -163,9 +168,11 @@ static unsigned long single_gpci_request(u32 req, u32 starting_index,
 	 */
 	count = 0;
 	for (i = offset; i < offset + length; i++)
-		count |= arg.bytes[i] << (i - offset);
+		count |= arg->bytes[i] << (i - offset);
 
 	*value = count;
+out:
+	put_cpu_var(hv_gpci_reqb);
 	return ret;
 }
 
@@ -245,10 +252,10 @@ static int h_gpci_event_init(struct perf_event *event)
 	}
 
 	/* last byte within the buffer? */
-	if ((event_get_offset(event) + length) > GPCI_MAX_DATA_BYTES) {
+	if ((event_get_offset(event) + length) > HGPCI_MAX_DATA_BYTES) {
 		pr_devel("request outside of buffer: %zu > %zu\n",
 				(size_t)event_get_offset(event) + length,
-				GPCI_MAX_DATA_BYTES);
+				HGPCI_MAX_DATA_BYTES);
 		return -EINVAL;
 	}
 
-- 
1.8.3.1