linux-kernel - [PATCH 06/10] random: use the arch-specific rng in xfer_secondary

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Date:	Thu,  5 Jul 2012 14:12:09 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>
Cc:	torvalds@...ux-foundation.org, w@....eu, ewust@...ch.edu,
	zakir@...ch.edu, greg@...ah.com, mpm@...enic.com,
	nadiah@...ucsd.edu, jhalderm@...ch.edu, tglx@...utronix.de,
	davem@...emloft.net, Theodore Ts'o <tytso@....edu>,
	stable@...nel.org
Subject: [PATCH 06/10] random: use the arch-specific rng in xfer_secondary_pool

If the CPU supports a hardware random number generator, use it in
xfer_secondary_pool(), where it will significantly improve things and
where we can afford it.

Also, remove the use of the arch-specific rng in
add_timer_randomness(), since the call is significantly slower than
get_cycles(), and we're much better off using it in
xfer_secondary_pool() anyway.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Cc: stable@...nel.org
---
 drivers/char/random.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 59ddcce..7f95f91 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -695,8 +695,8 @@ static struct timer_rand_state input_timer_state;
 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 {
 	struct {
+		cycles_t cycles;
 		long jiffies;
-		unsigned cycles;
 		unsigned num;
 	} sample;
 	long delta, delta2, delta3;
@@ -708,11 +708,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 		goto out;
 
 	sample.jiffies = jiffies;
-
-	/* Use arch random value, fall back to cycles */
-	if (!arch_get_random_int(&sample.cycles))
-		sample.cycles = get_cycles();
-
+	sample.cycles = get_cycles();
 	sample.num = num;
 	mix_pool_bytes(&input_pool, &sample, sizeof(sample));
 
@@ -831,7 +827,8 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
  */
 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
 {
-	__u32 tmp[OUTPUT_POOL_WORDS];
+	__u32	tmp[OUTPUT_POOL_WORDS];
+	int	i, hwrand[4];
 
 	if (r->pull && r->entropy_count < nbytes * 8 &&
 	    r->entropy_count < r->poolinfo->POOLBITS) {
@@ -853,6 +850,11 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
 		mix_pool_bytes(r, tmp, bytes);
 		credit_entropy_bits(r, bytes*8, 0);
 	}
+	for (i = 0; i < 4; i++)
+		if (arch_get_random_int(&hwrand[i]))
+			break;
+	if (i)
+		mix_pool_bytes(r, &hwrand, sizeof(hwrand));
 }
 
 /*
-- 
1.7.11.1.108.gb129051

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