linux-kernel - Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu

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Date:	Thu, 28 Apr 2016 16:18:23 -0600
From:	"Bruce Rogers" <brogers@...e.com>
To:	"Wanpeng Li" <kernellwp@...il.com>
Cc:	"Nadav Amit" <namit@...technion.ac.il>,
	"Paolo Bonzini" <pbonzini@...hat.com>,
	"J. Kiszka" <jan.kiszka@...mens.com>, "kvm" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization
 code in vmx_cpu_reset

>>> On 4/26/2016 at 08:54 PM, Wanpeng Li <kernellwp@...il.com> wrote: 
> 2016-02-09 0:29 GMT+08:00 Bruce Rogers <brogers@...e.com>:
>>>>> On 2/8/2016 at 08:09 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>>
>>>
>>> On 03/02/2016 23:51, Bruce Rogers wrote:
>>>>
>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>> index e2951b6..21507b4 100644
>>>> --- a/arch/x86/kvm/vmx.c
>>>> +++ b/arch/x86/kvm/vmx.c
>>>> @@ -4993,8 +4993,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool
>>> init_event)
>>>>              vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
>>>>
>>>>      cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET;
>>>> -    vmx_set_cr0(vcpu, cr0); /* enter rmode */
>>>>      vmx->vcpu.arch.cr0 = cr0;
>>>> +    vmx_set_cr0(vcpu, cr0); /* enter rmode */
>>>
>>> Your comment that the assignment is redundant is correct, but I am
>>> afraid that this fix is also wrong.  In particular, it would not cause
>>> exit_lmode and enter_rmode to be called.
>>>
>>> You are not describing which call to kvm_mmu_reset_context was messed
>>> up, so I'm not sure how your patch is fixing things.
>>
>> This is in the context of AP sending INIT to BSP with unrestricted_guest=N.
> 
> BSP will broadcast INIT-SIPI-SIPI sequence to APs during
> initialization, could you point out when "AP sending INIT to BSP" as
> you mentioned above in SDM?
> 

You should know that I abandoned this patch series as further investigation
revealed that this was not as cut and dried as I had first hoped.

Bruce