On 2013-03-14 13:18, Gleb Natapov wrote:
> On Thu, Mar 14, 2013 at 01:16:41PM +0100, Jan Kiszka wrote:
>> 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.
>>
> I agree. Lets try second approach. Can you write a patch?
Task queued for later today or tomorrow. I suppose you hold back this
patch here for now anyway.
Jan
--
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
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