linux-kernel - [PATCH RESEND v2 2/4] KVM: ensure grow start value is nonzero

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Date:   Wed,  6 Nov 2019 19:55:00 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com,
        rafael.j.wysocki@...el.com, joao.m.martins@...cle.com,
        mtosatti@...hat.com, kvm@...r.kernel.org, linux-pm@...r.kernel.org,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>
Subject: [PATCH RESEND v2 2/4] KVM: ensure grow start value is nonzero

vcpu->halt_poll_ns could be zeroed in certain cases (e.g. by
halt_poll_ns = 0). If halt_poll_grow_start is zero,
vcpu->halt_poll_ns will never be bigger than zero.

Use param callback to avoid writing zero to halt_poll_grow_start.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
---
 virt/kvm/kvm_main.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d6f0696..359516b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -69,6 +69,26 @@
 MODULE_AUTHOR("Qumranet");
 MODULE_LICENSE("GPL");
 
+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,
+};
+
 /* Architectures should define their poll value according to the halt latency */
 unsigned int halt_poll_ns = KVM_HALT_POLL_NS_DEFAULT;
 module_param(halt_poll_ns, uint, 0644);
@@ -81,7 +101,7 @@
 
 /* The start value to grow halt_poll_ns from */
 unsigned int halt_poll_ns_grow_start = 10000; /* 10us */
-module_param(halt_poll_ns_grow_start, uint, 0644);
+module_param_cb(halt_poll_ns_grow_start, &grow_start_ops, &halt_poll_ns_grow_start, 0644);
 EXPORT_SYMBOL_GPL(halt_poll_ns_grow_start);
 
 /* Default resets per-vcpu halt_poll_ns . */
-- 
1.8.3.1