linux-kernel - [PATCH 4/5] cpuidle-haltpoll: add a check to ensure grow start value is nonzero

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Date:   Sat, 26 Oct 2019 11:23:58 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     kvm@...r.kernel.org, mtosatti@...hat.com,
        joao.m.martins@...cle.com, rafael.j.wysocki@...el.com,
        rkrcmar@...hat.com, pbonzini@...hat.com,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>
Subject: [PATCH 4/5] cpuidle-haltpoll: add a check to ensure grow start value is nonzero

dev->poll_limit_ns could be zeroed in certain cases (e.g. by
guest_halt_poll_shrink). If guest_halt_poll_grow_start is zero,
dev->poll_limit_ns will never be larger than zero.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
---
 drivers/cpuidle/governors/haltpoll.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/cpuidle/governors/haltpoll.c b/drivers/cpuidle/governors/haltpoll.c
index 7a703d2..4b00d7a 100644
--- a/drivers/cpuidle/governors/haltpoll.c
+++ b/drivers/cpuidle/governors/haltpoll.c
@@ -77,7 +77,7 @@ static int haltpoll_select(struct cpuidle_driver *drv,
 
 static void adjust_poll_limit(struct cpuidle_device *dev, unsigned int block_us)
 {
-	unsigned int val;
+	unsigned int val, grow_start;
 	u64 block_ns = block_us*NSEC_PER_USEC;
 
 	/* Grow cpu_halt_poll_us if
@@ -86,8 +86,17 @@ static void adjust_poll_limit(struct cpuidle_device *dev, unsigned int block_us)
 	if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns) {
 		val = dev->poll_limit_ns * guest_halt_poll_grow;
 
-		if (val < guest_halt_poll_grow_start)
-			val = guest_halt_poll_grow_start;
+		/*
+		 * vcpu->halt_poll_ns needs a nonzero start point to grow if
+		 * it's zero.
+		 */
+		grow_start = guest_halt_poll_grow_start;
+		if (!grow_start)
+			grow_start = 1;
+
+		if (val < grow_start)
+			val = grow_start;
+
 		if (val > guest_halt_poll_ns)
 			val = guest_halt_poll_ns;
 
-- 
1.8.3.1