KVM: fix rcu usage in init_rmode_* functions

fix:
[ 3494.671786] stack backtrace:
[ 3494.671789] Pid: 10527, comm: qemu-system-x86 Not tainted 2.6.38-rc6+ #23
[ 3494.671790] Call Trace:
[ 3494.671796]  [] ? lockdep_rcu_dereference+0x9d/0xa5
[ 3494.671826]  [] ? kvm_memslots+0x6b/0x73 [kvm]
[ 3494.671834]  [] ? gfn_to_memslot+0x16/0x4f [kvm]
[ 3494.671843]  [] ? gfn_to_hva+0x16/0x27 [kvm]
[ 3494.671851]  [] ? kvm_write_guest_page+0x31/0x83 [kvm]
[ 3494.671861]  [] ? kvm_clear_guest_page+0x1a/0x1c [kvm]
[ 3494.671867]  [] ? vmx_set_tss_addr+0x83/0x122 [kvm_intel]

and:
[ 8328.789599] stack backtrace:
[ 8328.789601] Pid: 18736, comm: qemu-system-x86 Not tainted 2.6.38-rc6+ #23
[ 8328.789603] Call Trace:
[ 8328.789609]  [] ? lockdep_rcu_dereference+0x9d/0xa5
[ 8328.789621]  [] ? kvm_memslots+0x6b/0x73 [kvm]
[ 8328.789628]  [] ? gfn_to_memslot+0x16/0x4f [kvm]
[ 8328.789635]  [] ? gfn_to_hva+0x16/0x27 [kvm]
[ 8328.789643]  [] ? kvm_write_guest_page+0x31/0x83 [kvm]
[ 8328.789699]  [] ? kvm_clear_guest_page+0x1a/0x1c [kvm]
[ 8328.789713]  [] ? vmx_create_vcpu+0x316/0x3c8 [kvm_intel]
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -2397,11 +2397,12 @@ static bool guest_state_valid(struct kvm_vcpu *vcpu)
 
 static int init_rmode_tss(struct kvm *kvm)
 {
-	gfn_t fn = rmode_tss_base(kvm) >> PAGE_SHIFT;
+	gfn_t fn;
 	u16 data = 0;
-	int ret = 0;
-	int r;
+	int r, idx, ret = 0;
 
+	idx = srcu_read_lock(&kvm->srcu);
+	fn = rmode_tss_base(kvm) >> PAGE_SHIFT;
 	r = kvm_clear_guest_page(kvm, fn, 0, PAGE_SIZE);
 	if (r < 0)
 		goto out;
@@ -2425,12 +2426,13 @@ static int init_rmode_tss(struct kvm *kvm)
 
 	ret = 1;
 out:
+	srcu_read_unlock(&kvm->srcu, idx);
 	return ret;
 }
 
 static int init_rmode_identity_map(struct kvm *kvm)
 {
-	int i, r, ret;
+	int i, idx, r, ret;
 	pfn_t identity_map_pfn;
 	u32 tmp;
 
@@ -2445,6 +2447,7 @@ static int init_rmode_identity_map(struct kvm *kvm)
 		return 1;
 	ret = 0;
 	identity_map_pfn = kvm->arch.ept_identity_map_addr >> PAGE_SHIFT;
+	idx = srcu_read_lock(&kvm->srcu);
 	r = kvm_clear_guest_page(kvm, identity_map_pfn, 0, PAGE_SIZE);
 	if (r < 0)
 		goto out;
@@ -2460,6 +2463,7 @@ static int init_rmode_identity_map(struct kvm *kvm)
 	kvm->arch.ept_identity_pagetable_done = true;
 	ret = 1;
 out:
+	srcu_read_unlock(&kvm->srcu, idx);
 	return ret;
 }