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Re: [PATCH] KVM: x86: fix eflags state following processor init/reset

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  Re: [PATCH] KVM: x86: fix eflags state following processor init/reset Paolo Bonzini <pbonzini@redhat.com> - 2015-11-03 11:50 +0100
    Re: [PATCH] KVM: x86: fix eflags state following processor init/reset Wanpeng Li <kernellwp@gmail.com> - 2015-11-11 07:40 +0100

#1261378 — Re: [PATCH] KVM: x86: fix eflags state following processor init/reset

On 28/10/2015 09:10, Nadav Amit wrote:
> Here are my 5 cents. Note that vmx_vcpu_reset calls:
> 
> 	vmcs_writel(GUEST_RFLAGS, 0x02);
> 
> (And the RFLAGS value is not cached by KVM, so no consistency problem should
> occur.)
> 
> You may want to change the value into constant or call a wrapper function
> for setting RFLAGS, but I don’t see something broken in the functionality.

I agree.  Wanpeng, if this is just a cleanup, can you send v2 that
removes or modifies the existing call to vmcs_writel?  If there is a
bug, can you write a unit test for it?  It should be possible to test
for the problem using INIT+SIPI on an AP.

Thanks,

Paolo

> Regards,
> Nadav
> 
> Wanpeng Li <wanpeng.li@hotmail.com> wrote:
> 
>> Ping, :-)
>> On 10/21/15 2:28 PM, Wanpeng Li wrote:
>>> Reference SDM 3.4.3:
>>>
>>> Following initialization of the processor (either by asserting the
>>> RESET pin or the INIT pin), the state of the EFLAGS register is
>>> 00000002H.
>>>
>>> However, the eflags fixed bit is not set and other bits are also not
>>> cleared during the init/reset in kvm.
>>>
>>> This patch fix it by set eflags register to 00000002H following
>>> initialization of the processor.
>>>
>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>>> ---
>>>  arch/x86/kvm/vmx.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index b680c2e..326f6ea 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -4935,6 +4935,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>>  	vmx_set_efer(vcpu, 0);
>>>  	vmx_fpu_activate(vcpu);
>>>  	update_exception_bitmap(vcpu);
>>> +	vmx_set_rflags(vcpu, X86_EFLAGS_FIXED);
>>>    	vpid_sync_context(vmx->vpid);
>>>  }
>>
>> --
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> 
> 
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#1266986

2015-11-03 18:47 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 28/10/2015 09:10, Nadav Amit wrote:
>> Here are my 5 cents. Note that vmx_vcpu_reset calls:
>>
>>       vmcs_writel(GUEST_RFLAGS, 0x02);
>>
>> (And the RFLAGS value is not cached by KVM, so no consistency problem should
>> occur.)
>>
>> You may want to change the value into constant or call a wrapper function
>> for setting RFLAGS, but I don’t see something broken in the functionality.
>
> I agree.  Wanpeng, if this is just a cleanup, can you send v2 that
> removes or modifies the existing call to vmcs_writel?  If there is a
> bug, can you write a unit test for it?  It should be possible to test
> for the problem using INIT+SIPI on an AP.

You are right, I write a INIT+SIPI kvm-unit-test and didn't trigger
any bug. Please ignore the patch.

Regards,
Wanpeng Li
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