linux-kernel - Re: [PATCH] KVM: x86: fix access memslots w/o hold srcu read lock

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Date:	Fri, 31 Oct 2014 11:36:43 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Chen, Tiejun" <tiejun.chen@...el.com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
CC:	Gleb Natapov <gleb@...nel.org>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Takashi Iwai <tiwai@...e.de>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: fix access memslots w/o hold srcu read lock



On 31/10/2014 06:30, Chen, Tiejun wrote:
> 
> @@ -4442,6 +4442,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
>  {
>         struct vcpu_vmx *vmx = to_vmx(vcpu);
>         struct msr_data apic_base_msr;
> +       int idx;
> 
>         vmx->rmode.vm86_active = 0;
> 
> @@ -4509,7 +4510,9 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
>                 vmcs_write32(TPR_THRESHOLD, 0);
>         }
> 
> +       idx = srcu_read_lock(&vcpu->kvm->srcu);
>         kvm_vcpu_reload_apic_access_page(vcpu);
> +       srcu_read_unlock(&vcpu->kvm->srcu, idx);
> 
>         if (vmx_vm_has_apicv(vcpu->kvm))
>                 memset(&vmx->pi_desc, 0, sizeof(struct pi_desc));

Not enough; you can call vcpu_enter_guest -> kvm_apic_accept_events ->
kvm_vcpu_reset -> vmx_vcpu_reset while under the SRCU lock.  The right
place to add the lock is kvm_arch_vcpu_setup.

Thanks,

Paolo
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