linux-kernel - Re: [PATCH 2/4] KVM: document memory barriers for kvm->vcpus/kvm->online

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <55BA2F3A.8060501@de.ibm.com>
Date:	Thu, 30 Jul 2015 16:05:46 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
CC:	mtosatti@...hat.com, srutherford@...gle.com, rkrcmar@...hat.com
Subject: Re: [PATCH 2/4] KVM: document memory barriers for kvm->vcpus/kvm->online_vcpus

Am 30.07.2015 um 16:02 schrieb Paolo Bonzini:
> 
> 
> On 30/07/2015 15:57, Christian Borntraeger wrote:
>>>>>> +	/* Pairs with smp_wmb() in kvm_vm_ioctl_create_vcpu, in case
>>>>>> +	 * the caller has read kvm->online_vcpus before (as is the case
>>>>>> +	 * for kvm_for_each_vcpu, for example).
>>>>>> +	 */
>> is somewhat distracting because of "read" and "before". So something like
>>
>>  /* Pairs with smp_wmb() in kvm_vm_ioctl_create_vcpu, to serialize the setting
>> of kvm->vcpus and setting kvm->online_vcpus....
>>
>> might be better.
> 
> What you are suggesting would go in kvm_vm_ioctl_create_vcpu, e.g.
> rewriting:
> 
> 	/* Pairs with smp_rmb() in kvm_get_vcpu.  */
> 	smp_wmb();
> 
> like this:
> 
> 	/*
> 	 * Pairs with smp_rmb() in kvm_get_vcpu.  Write kvm->vcpus
> 	 * before kvm->online_vcpu's incremented value.
> 	 */
> 	smp_wmb();
> 
> Instead, kvm_get_cpu has:
> 
> 	/*
> 	 * Pairs with smp_wmb() in kvm_vm_ioctl_create_vcpu, in case
> 	 * the caller has read kvm->online_vcpus before (as is the case
> 	 * for kvm_for_each_vcpu, for example).
> 	 */
> 	smp_rmb();
> 
> which already describes which loads are serialized here.
> 
> Is this correct?

Right you are.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/