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From:   Zhenzhong Duan <zhenzhong.duan@oracle.com>
To:     linux-kernel@vger.kernel.org
Cc:     pbonzini@redhat.com, rkrcmar@redhat.com,
        rafael.j.wysocki@intel.com, joao.m.martins@oracle.com,
        mtosatti@redhat.com, kvm@vger.kernel.org, linux-pm@vger.kernel.org,
        Zhenzhong Duan <zhenzhong.duan@oracle.com>
Subject: [PATCH RESEND v2 1/4] cpuidle-haltpoll: ensure grow start value is nonzero
Date:   Wed,  6 Nov 2019 19:54:59 +0800
Message-Id: <1573041302-4904-2-git-send-email-zhenzhong.duan@oracle.com>
In-Reply-To: <1573041302-4904-1-git-send-email-zhenzhong.duan@oracle.com>
References: <1573041302-4904-1-git-send-email-zhenzhong.duan@oracle.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

dev->poll_limit_ns could be zeroed in certain cases (e.g. by
guest_halt_poll_ns = 0). If guest_halt_poll_grow_start is zero,
dev->poll_limit_ns will never be bigger than zero.

Use param callback to avoid writing zero to guest_halt_poll_grow_start.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
---
 drivers/cpuidle/governors/haltpoll.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/cpuidle/governors/haltpoll.c b/drivers/cpuidle/governors/haltpoll.c
index 7a703d2..660859d 100644
--- a/drivers/cpuidle/governors/haltpoll.c
+++ b/drivers/cpuidle/governors/haltpoll.c
@@ -20,6 +20,26 @@
 #include <linux/module.h>
 #include <linux/kvm_para.h>
 
+static int grow_start_set(const char *val, const struct kernel_param *kp)
+{
+	int ret;
+	unsigned int n;
+
+	if (!val)
+		return -EINVAL;
+
+	ret = kstrtouint(val, 0, &n);
+	if (ret || !n)
+		return -EINVAL;
+
+	return param_set_uint(val, kp);
+}
+
+static const struct kernel_param_ops grow_start_ops = {
+	.set = grow_start_set,
+	.get = param_get_uint,
+};
+
 static unsigned int guest_halt_poll_ns __read_mostly = 200000;
 module_param(guest_halt_poll_ns, uint, 0644);
 
@@ -33,7 +53,7 @@
 
 /* value in us to start growing per-cpu halt_poll_ns */
 static unsigned int guest_halt_poll_grow_start __read_mostly = 50000;
-module_param(guest_halt_poll_grow_start, uint, 0644);
+module_param_cb(guest_halt_poll_grow_start, &grow_start_ops, &guest_halt_poll_grow_start, 0644);
 
 /* allow shrinking guest halt poll */
 static bool guest_halt_poll_allow_shrink __read_mostly = true;
-- 
1.8.3.1