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

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Date:	Wed, 28 Oct 2015 10:10:34 +0200
From:	Nadav Amit <nadav.amit@...il.com>
To:	Wanpeng Li <wanpeng.li@...mail.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: fix eflags state following processor init/reset

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.

Regards,
Nadav

Wanpeng Li <wanpeng.li@...mail.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@...mail.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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