linux-kernel - Re: [PATCH 05/47] KVM: VMX: Optimize vmx_get

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Message-ID: <4A9547A6.1000902@redhat.com>
Date:	Wed, 26 Aug 2009 17:33:10 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Roel Kluin <roel.kluin@...il.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/47] KVM: VMX: Optimize vmx_get_cpl()

On 08/26/2009 05:15 PM, Roel Kluin wrote:
> Op 26-08-09 12:29, Avi Kivity schreef:
>    
>> Instead of calling vmx_get_segment() (which reads a whole bunch of
>> vmcs fields), read only the cs selector which contains the cpl.
>>
>> Signed-off-by: Avi Kivity<avi@...hat.com>
>>      
> Can't we also optimise cs_ss_rpl_check()? (Please review, untested.)
>
> ------------->8 ---------------------- 8<  --------------------
> Instead of calling vmx_get_segment() (which reads a whole bunch of
> vmcs fields), read only the cs/ss selectors which contains the rpls.
>
>    

It's really a slowpath, so I prefer not to touch it.  We're likely to 
start caching guest segment fields soon, so the less code that reads 
them directly, the better.

> Signed-off-by: Roel Kluin<roel.kluin@...il.com>
> ---
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 29f9129..5d8512a 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1932,13 +1932,8 @@ static bool ldtr_valid(struct kvm_vcpu *vcpu)
>
>   static bool cs_ss_rpl_check(struct kvm_vcpu *vcpu)
>   {
> -	struct kvm_segment cs, ss;
> -
> -	vmx_get_segment(vcpu,&cs, VCPU_SREG_CS);
> -	vmx_get_segment(vcpu,&ss, VCPU_SREG_SS);
> -
> -	return ((cs.selector&  SELECTOR_RPL_MASK) ==
> -		 (ss.selector&  SELECTOR_RPL_MASK));
> +	return ((vmcs_read16(GUEST_CS_SELECTOR)&  SELECTOR_RPL_MASK) ==
> +		 (vmcs_read16(GUEST_SS_SELECTOR)&  SELECTOR_RPL_MASK));
>   }
>
>   /*
>    


-- 
error compiling committee.c: too many arguments to function

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