Re: [PATCH v2] KVM: x86: Rework INIT and SIPI handling

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2013-03-14 13:12, Gleb Natapov wrote:
> On Thu, Mar 14, 2013 at 12:29:48PM +0100, Jan Kiszka wrote:
>> On 2013-03-14 11:15, Jan Kiszka wrote:
>>>>>  
>>>>> -	if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED)) {
>>>>> -		pr_debug("vcpu %d received sipi with vector # %x\n",
>>>>> -			 vcpu->vcpu_id, vcpu->arch.sipi_vector);
>>>>> -		kvm_lapic_reset(vcpu);
>>>>> -		kvm_vcpu_reset(vcpu);
>>>>> -		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
>>>>> -	}
>>>>> -
>>>>>  	vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
>>>>>  	r = vapic_enter(vcpu);
>>>>
>>>> vmx_vcpu_reset overwrites vcpu->srcu_idx if ->vcpu_reset is called from
>>>> within srcu section.
>>>
>>> Indeed.
>>>
>>> Do you know what the look over vmx_set_cr0 actually protects?
>>
>> Found it: It's not actually protecting anything. enter_rmode is called,
>> and that assumes that lock to be held. If enter_rmode faces an
>> uninitialized tss, it drops the lock before calling vmx_set_tss_addr.
>>
>> Well, I wonder if that is a good place to fix the TSS issue. Why not
>> make that special case (lacking KVM_SET_TSS_ADDR before first KVM_RUN) a
>> static jump key and check for it on KVM_RUN?
>>
> Or finally break userspace that does not set it before calling kvm_run.
> I haven't seen people complain about "kvm: KVM_SET_TSS_ADDR need to be
> called before entering vcpu" warning in dmesg. Or create TSS mem slot at
> 0xfeffd000 during VM creation and destroy it if userspace overwrites it.

Whatever is preferred, I'm not able to decide (about ABI "breakage"
specifically). I just think any of them would be better than pulling
vcpu_reset out of the inner loop again just to fulfill the locking
requirements.

Jan

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