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Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like APs do

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>>> On 2/8/2016 at 08:22 AM, Jan Kiszka <jan.kiszka@web.de> wrote: 
> On 2016-02-08 16:12, Paolo Bonzini wrote:
>> 
>> 
>> On 03/02/2016 23:51, Bruce Rogers wrote:
>>> The INIT IPI event handler special cases the boot-strap processor
>>> (BSP) handling, avoiding the same mp state handling which is done for
>>> the other (AP) processors. Debugging a linux guest usage scenario of
>>> avoiding a reboot through the bios for a crash on any processor via eg:
>>> kexec -p /boot/vmlinuz --initrd=/boot/initrd --append="$(cat /proc/cmdline)\
>>> maxcpus=1" led to identifying this change as the needed fix.
>>>
>>> With this change, an AP can now startup the BSP without error.
>>>
>>> Signed-off-by: Bruce Rogers <brogers@suse.com>
>>> ---
>>>  arch/x86/kvm/lapic.c | 5 +----
>>>  1 file changed, 1 insertion(+), 4 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>>> index 36591fa..eda6bfb 100644
>>> --- a/arch/x86/kvm/lapic.c
>>> +++ b/arch/x86/kvm/lapic.c
>>> @@ -2170,10 +2170,7 @@ void kvm_apic_accept_events(struct kvm_vcpu *vcpu)
>>>  	if (test_bit(KVM_APIC_INIT, &pe)) {
>>>  		kvm_lapic_reset(vcpu, true);
>>>  		kvm_vcpu_reset(vcpu, true);
>>> -		if (kvm_vcpu_is_bsp(apic->vcpu))
>>> -			vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
>>> -		else
>>> -			vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
>>> +		vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
>>>  	}
>>>  	if (test_bit(KVM_APIC_SIPI, &pe) &&
>>>  	    vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
>>>
>> 
>> KVM_MP_STATE_INIT_RECEIVED is what Intel calls the "wait for SIPI"
>> state.  The BSP never gets a SIPI, it goes straight to 0xFFFFFFF0
>> instead.  Can you explain the problem more in detail?
> 
> I suspect this is about sending INIT-SIPI from another CPU, directed to
> the BSP, isn't it? We may have to differentiate between CPU (including
> system) reset and that IPI case.

That is correct. In looking over the KVM code which deals with BSP, this was
the only place which seemed wrong to me wrt special casing for BSP outside the
context of initial system initialization / reset. As far as I understand the BSP shouldn't
be treated differently in this case.

Bruce

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[PATCH 1/2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu_reset Bruce Rogers <brogers@suse.com> - 2016-02-04 00:20 +0100
  [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like APs do Bruce Rogers <brogers@suse.com> - 2016-02-04 00:20 +0100
    Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like APs do Paolo Bonzini <pbonzini@redhat.com> - 2016-02-08 16:20 +0100
      Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like APs do Jan Kiszka <jan.kiszka@web.de> - 2016-02-08 16:30 +0100
        Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like  APs do "Bruce Rogers" <brogers@suse.com> - 2016-02-08 17:40 +0100
          Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like APs do Paolo Bonzini <pbonzini@redhat.com> - 2016-02-08 17:50 +0100
            Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like  APs do "Bruce Rogers" <brogers@suse.com> - 2016-02-08 18:30 +0100
              Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like APs do Paolo Bonzini <pbonzini@redhat.com> - 2016-02-08 18:50 +0100
            Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like  APs do "Bruce Rogers" <brogers@suse.com> - 2016-02-08 18:40 +0100
              Re: [PATCH 2/2] KVM: x86: allow BSP to handle INIT IPIs like APs do Jan Kiszka <jan.kiszka@web.de> - 2016-02-08 19:00 +0100
  Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu_reset Nadav Amit <nadav.amit@gmail.com> - 2016-02-04 00:20 +0100
    Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization  code in vmx_cpu_reset "Bruce Rogers" <brogers@suse.com> - 2016-02-04 00:40 +0100
  Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization code in  vmx_cpu_reset Paolo Bonzini <pbonzini@redhat.com> - 2016-02-08 16:10 +0100
    Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization  code in vmx_cpu_reset "Bruce Rogers" <brogers@suse.com> - 2016-02-08 17:30 +0100
      Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization code in  vmx_cpu_reset Paolo Bonzini <pbonzini@redhat.com> - 2016-02-08 17:50 +0100

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