linux-kernel - Re: [PATCH] KVM: VMX: replace move_msr

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Message-ID: <20171106071427.Horde.S9Js9jxe-hQCvJQaKhHNRgZ@gator4166.hostgator.com>
Date:   Mon, 06 Nov 2017 07:14:27 -0600
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: VMX: replace move_msr_up with swap macro

Hi Paolo,

Quoting Paolo Bonzini <pbonzini@...hat.com>:

> ----- Original Message -----
>> From: "Gustavo A. R. Silva" <garsilva@...eddedor.com>
>> To: "Paolo Bonzini" <pbonzini@...hat.com>, "Radim Krčmář"  
>> <rkrcmar@...hat.com>, "Thomas Gleixner"
>> <tglx@...utronix.de>, "Ingo Molnar" <mingo@...hat.com>, "H. Peter  
>> Anvin" <hpa@...or.com>, x86@...nel.org
>> Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, "Gustavo A.  
>> R. Silva" <garsilva@...eddedor.com>
>> Sent: Friday, November 3, 2017 11:58:19 PM
>> Subject: [PATCH] KVM: VMX: replace move_msr_up with swap macro
>>
>> Function move_msr_up is used to _manually_ swap MSR entries in MSR array.
>> This function can be removed and replaced using the swap macro instead.
>>
>> This code was detected with the help of Coccinelle.
>
> I think move_msr_up should instead change into a function like
>
>    void mark_msr_for_save(struct vcpu_vmx *vmx, int index)
>    {
>        swap(vmx->guest_msrs[index], vmx->guest_msrs[vmx->save_nmsrs]);
>        vmx->save_nmsrs++;
>    }
>
> Using swap is useful, but it is also hiding what's going on exactly
> (in addition, using ++ inside a macro argument might be calling for
> trouble).
>

Thanks for your comments.

I'll work on v2 based on your feedback.

--
Gustavo A. R. Silva

> Paolo
>
>>
>> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
>> ---
>> The new lines are over 80 characters, but I think in this case that is
>> preferable over splitting them.
>>
>>  arch/x86/kvm/vmx.c | 24 ++++++------------------
>>  1 file changed, 6 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index e6c8ffa..210e491 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2544,18 +2544,6 @@ static bool vmx_invpcid_supported(void)
>>  	return cpu_has_vmx_invpcid() && enable_ept;
>>  }
>>
>> -/*
>> - * Swap MSR entry in host/guest MSR entry array.
>> - */
>> -static void move_msr_up(struct vcpu_vmx *vmx, int from, int to)
>> -{
>> -	struct shared_msr_entry tmp;
>> -
>> -	tmp = vmx->guest_msrs[to];
>> -	vmx->guest_msrs[to] = vmx->guest_msrs[from];
>> -	vmx->guest_msrs[from] = tmp;
>> -}
>> -
>>  static void vmx_set_msr_bitmap(struct kvm_vcpu *vcpu)
>>  {
>>  	unsigned long *msr_bitmap;
>> @@ -2600,28 +2588,28 @@ static void setup_msrs(struct vcpu_vmx *vmx)
>>  	if (is_long_mode(&vmx->vcpu)) {
>>  		index = __find_msr_index(vmx, MSR_SYSCALL_MASK);
>>  		if (index >= 0)
>> -			move_msr_up(vmx, index, save_nmsrs++);
>> +			swap(vmx->guest_msrs[index], vmx->guest_msrs[save_nmsrs++]);
>>  		index = __find_msr_index(vmx, MSR_LSTAR);
>>  		if (index >= 0)
>> -			move_msr_up(vmx, index, save_nmsrs++);
>> +			swap(vmx->guest_msrs[index], vmx->guest_msrs[save_nmsrs++]);
>>  		index = __find_msr_index(vmx, MSR_CSTAR);
>>  		if (index >= 0)
>> -			move_msr_up(vmx, index, save_nmsrs++);
>> +			swap(vmx->guest_msrs[index], vmx->guest_msrs[save_nmsrs++]);
>>  		index = __find_msr_index(vmx, MSR_TSC_AUX);
>>  		if (index >= 0 && guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP))
>> -			move_msr_up(vmx, index, save_nmsrs++);
>> +			swap(vmx->guest_msrs[index], vmx->guest_msrs[save_nmsrs++]);
>>  		/*
>>  		 * MSR_STAR is only needed on long mode guests, and only
>>  		 * if efer.sce is enabled.
>>  		 */
>>  		index = __find_msr_index(vmx, MSR_STAR);
>>  		if ((index >= 0) && (vmx->vcpu.arch.efer & EFER_SCE))
>> -			move_msr_up(vmx, index, save_nmsrs++);
>> +			swap(vmx->guest_msrs[index], vmx->guest_msrs[save_nmsrs++]);
>>  	}
>>  #endif
>>  	index = __find_msr_index(vmx, MSR_EFER);
>>  	if (index >= 0 && update_transition_efer(vmx, index))
>> -		move_msr_up(vmx, index, save_nmsrs++);
>> +		swap(vmx->guest_msrs[index], vmx->guest_msrs[save_nmsrs++]);
>>
>>  	vmx->save_nmsrs = save_nmsrs;
>
>
>>
>> --
>> 2.7.4
>>
>>