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

[Sukadev Bhattiprolu]

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).

Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/perf/hv-gpci.c | 37 ++++++++++++++++++++++---------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
index 856fe6e..e6fad73 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 HGPCI_REQ_BUFFER_SIZE	4096
 #define GPCI_MAX_DATA_BYTES \
-	(1024 - sizeof(struct hv_get_perf_counter_info_params))
+	(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[1];
+} __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;
 }
 
-- 
1.8.3.1