linux-kernel - [PATCH] KVM: Use call_rcu() in kvm_io_bus_register

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Message-ID: <20250423092509.3162-1-lirongqing@baidu.com>
Date: Wed, 23 Apr 2025 17:25:09 +0800
From: lirongqing <lirongqing@...du.com>
To: <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
CC: Li RongQing <lirongqing@...du.com>, lizhaoxin <lizhaoxin04@...du.com>
Subject: [PATCH] KVM: Use call_rcu() in kvm_io_bus_register_dev

From: Li RongQing <lirongqing@...du.com>

Use call_rcu() instead of costly synchronize_srcu_expedited(), this
can reduce the VM bootup time, and reduce VM migration downtime

Signed-off-by: lizhaoxin <lizhaoxin04@...du.com>
Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 include/linux/kvm_host.h |  1 +
 virt/kvm/kvm_main.c      | 11 +++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 291d49b..e772704 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -203,6 +203,7 @@ struct kvm_io_range {
 #define NR_IOBUS_DEVS 1000
 
 struct kvm_io_bus {
+	struct rcu_head rcu;
 	int dev_count;
 	int ioeventfd_count;
 	struct kvm_io_range range[];
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2e591cc..af730a5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5865,6 +5865,13 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
 	return r < 0 ? r : 0;
 }
 
+static void free_kvm_io_bus(struct rcu_head *rcu)
+{
+	struct kvm_io_bus *bus = container_of(rcu, struct kvm_io_bus, rcu);
+
+	kfree(bus);
+}
+
 int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 			    int len, struct kvm_io_device *dev)
 {
@@ -5903,8 +5910,8 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 	memcpy(new_bus->range + i + 1, bus->range + i,
 		(bus->dev_count - i) * sizeof(struct kvm_io_range));
 	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
-	synchronize_srcu_expedited(&kvm->srcu);
-	kfree(bus);
+
+	call_srcu(&kvm->srcu, &bus->rcu, free_kvm_io_bus);
 
 	return 0;
 }
-- 
2.9.4