linux-kernel - Re: [PATCH] x86: kvm: hide the unused 'cpu' variable

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Date:   Wed, 4 Apr 2018 19:00:35 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Hildenbrand <david@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: kvm: hide the unused 'cpu' variable

On 04/04/2018 13:51, David Hildenbrand wrote:
> On 04.04.2018 12:44, Arnd Bergmann wrote:
>> The local variable was newly introduced but is only accessed in one
>> place on x86_64, but not on 32-bit:
>>
>> arch/x86/kvm/vmx.c: In function 'vmx_save_host_state':
>> arch/x86/kvm/vmx.c:2175:6: error: unused variable 'cpu' [-Werror=unused-variable]
>>
>> This puts it into another #ifdef.
>>
>> Fixes: 35060ed6a1ff ("x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE")
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>>  arch/x86/kvm/vmx.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 8307f625ea99..7399a4a17f78 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2357,7 +2357,9 @@ static unsigned long segment_base(u16 selector)
>>  static void vmx_save_host_state(struct kvm_vcpu *vcpu)
>>  {
>>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>> +#ifdef CONFIG_X86_64
>>  	int cpu = raw_smp_processor_id();
>> +#endif
>>  	int i;
>>  
>>  	if (vmx->host_state.loaded)
>>
> 
> Can't we get rid of the variable and just do it inline?

Neither is particularly nice, but one thing we can do is simplify the
#ifdef maze by combining conditionals that have no code in between.

Paolo

> Anyhow, fixes the problem
> 
> Reviewed-by: David Hildenbrand <david@...hat.com>
>