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

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Message-ID: <CANRm+CzYKgEK04s67MJj41rVpEq_C6z2s9m+UA2J2T-uDEnAUQ@mail.gmail.com>
Date:	Wed, 27 Apr 2016 10:54:36 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Bruce Rogers <brogers@...e.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, kvm <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nadav Amit <namit@...technion.ac.il>,
	"J. Kiszka" <jan.kiszka@...mens.com>
Subject: Re: [PATCH 1/2] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu_reset

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?

Regards,
Wanpeng Li