linux-kernel - Re: [PATCH 0/3] KVM: do not use kvm->online_vcpus to check "has one VCPU been created?"

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Date:	Thu, 16 Jun 2016 10:23:17 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Christian Borntraeger <christian.borntraeger@...ibm.com>
Subject: Re: [PATCH 0/3] KVM: do not use kvm->online_vcpus to check "has one
 VCPU been created?"



On 16/06/2016 09:59, Cornelia Huck wrote:
> On Thu, 16 Jun 2016 09:30:34 +0200
> Christian Borntraeger <borntraeger@...ibm.com> wrote:
> 
>> On 06/16/2016 12:00 AM, Paolo Bonzini wrote:
>>>
>>>
>>> On 13/06/2016 16:44, Cornelia Huck wrote:
>>>>>>  arch/s390/kvm/kvm-s390.c | 10 +++++-----
>>>>>>  arch/x86/kvm/Kconfig     |  1 -
>>>>>>  arch/x86/kvm/x86.c       | 11 +++--------
>>>>>>  include/linux/kvm_host.h | 14 ++++++++------
>>>>>>  virt/kvm/Kconfig         |  3 ---
>>>>>>  virt/kvm/kvm_main.c      | 27 +++++++++++++++++----------
>>>>>>  6 files changed, 33 insertions(+), 33 deletions(-)
>>>>>>
>>>> Looks like a sane approach, only two inversions in the s390 patch :)
>>>
>>> So it's okay to push patch 3 to kvm/next?
>>
>>
>> With the 2 fixes that Conny requested, yes.
> 
> I had been waiting for a v2 ;)

This is the patch I've pushed:

-------------------- 8< ---------------------
>From a03825bbd0c39feeba605912cdbc28e79e4e01e1 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@...hat.com>
Date: Mon, 13 Jun 2016 14:50:04 +0200
Subject: [PATCH] KVM: s390: use kvm->created_vcpus

The new created_vcpus field avoids possible races between enabling
capabilities and creating VCPUs.

Acked-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 49c60393a15c..0dcf9b8fc12c 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -422,7 +422,7 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
 		break;
 	case KVM_CAP_S390_VECTOR_REGISTERS:
 		mutex_lock(&kvm->lock);
-		if (atomic_read(&kvm->online_vcpus)) {
+		if (kvm->created_vcpus) {
 			r = -EBUSY;
 		} else if (MACHINE_HAS_VX) {
 			set_kvm_facility(kvm->arch.model.fac_mask, 129);
@@ -437,7 +437,7 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
 	case KVM_CAP_S390_RI:
 		r = -EINVAL;
 		mutex_lock(&kvm->lock);
-		if (atomic_read(&kvm->online_vcpus)) {
+		if (kvm->created_vcpus) {
 			r = -EBUSY;
 		} else if (test_facility(64)) {
 			set_kvm_facility(kvm->arch.model.fac_mask, 64);
@@ -492,7 +492,7 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
 		ret = -EBUSY;
 		VM_EVENT(kvm, 3, "%s", "ENABLE: CMMA support");
 		mutex_lock(&kvm->lock);
-		if (atomic_read(&kvm->online_vcpus) == 0) {
+		if (!kvm->created_vcpus) {
 			kvm->arch.use_cmma = 1;
 			ret = 0;
 		}
@@ -536,7 +536,7 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
 
 		ret = -EBUSY;
 		mutex_lock(&kvm->lock);
-		if (atomic_read(&kvm->online_vcpus) == 0) {
+		if (!kvm->created_vcpus) {
 			/* gmap_alloc will round the limit up */
 			struct gmap *new = gmap_alloc(current->mm, new_limit);
 
@@ -713,7 +713,7 @@ static int kvm_s390_set_processor(struct kvm *kvm, struct kvm_device_attr *attr)
 	int ret = 0;
 
 	mutex_lock(&kvm->lock);
-	if (atomic_read(&kvm->online_vcpus)) {
+	if (kvm->created_vcpus) {
 		ret = -EBUSY;
 		goto out;
 	}