linux-kernel - Re: [PATCH 05/15] KVM: MTRR: clean up mtrr default type

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Message-ID: <556C21BF.3090003@redhat.com>
Date:	Mon, 01 Jun 2015 11:11:27 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
CC:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/15] KVM: MTRR: clean up mtrr default type



On 30/05/2015 12:59, Xiao Guangrong wrote:
> Use union definition to avoid the decode/code workload and drop all the
> hard code
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 12 ++++++++++--
>  arch/x86/kvm/mtrr.c             | 19 ++++++++-----------
>  2 files changed, 18 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 2c3c52d..95ce2ff 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -347,8 +347,16 @@ enum {
>  struct kvm_mtrr {
>  	struct mtrr_var_range var_ranges[KVM_NR_VAR_MTRR];
>  	mtrr_type fixed_ranges[KVM_NR_FIXED_MTRR_REGION];
> -	unsigned char enabled;
> -	mtrr_type def_type;
> +
> +	union {
> +		u64 deftype;
> +		struct {
> +			unsigned def_type:8;
> +			unsigned reserved:2;
> +			unsigned fixed_mtrr_enabled:1;
> +			unsigned mtrr_enabled:1;
> +		};
> +	};
>  };
>  
>  struct kvm_vcpu_arch {
> diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
> index 562341b..6de49dd 100644
> --- a/arch/x86/kvm/mtrr.c
> +++ b/arch/x86/kvm/mtrr.c
> @@ -105,7 +105,6 @@ EXPORT_SYMBOL_GPL(kvm_mtrr_valid);
>  static void update_mtrr(struct kvm_vcpu *vcpu, u32 msr)
>  {
>  	struct kvm_mtrr *mtrr_state = &vcpu->arch.mtrr_state;
> -	unsigned char mtrr_enabled = mtrr_state->enabled;
>  	gfn_t start, end, mask;
>  	int index;
>  	bool is_fixed = true;
> @@ -114,7 +113,7 @@ static void update_mtrr(struct kvm_vcpu *vcpu, u32 msr)
>  	      !kvm_arch_has_noncoherent_dma(vcpu->kvm))
>  		return;
>  
> -	if (!(mtrr_enabled & 0x2) && msr != MSR_MTRRdefType)
> +	if (!mtrr_state->mtrr_enabled && msr != MSR_MTRRdefType)

I know Linus doesn't like bitfields too much.  Can you change these to
inline functions, and only leave an "u64 deftype" in the struct?

Paolo

>  		return;
>  
>  	switch (msr) {
> @@ -153,7 +152,7 @@ static void update_mtrr(struct kvm_vcpu *vcpu, u32 msr)
>  		end = ((start & mask) | ~mask) + 1;
>  	}
>  
> -	if (is_fixed && !(mtrr_enabled & 0x1))
> +	if (is_fixed && !mtrr_state->fixed_mtrr_enabled)
>  		return;
>  
>  	kvm_zap_gfn_range(vcpu->kvm, gpa_to_gfn(start), gpa_to_gfn(end));
> @@ -166,10 +165,9 @@ int kvm_mtrr_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>  	if (!kvm_mtrr_valid(vcpu, msr, data))
>  		return 1;
>  
> -	if (msr == MSR_MTRRdefType) {
> -		vcpu->arch.mtrr_state.def_type = data;
> -		vcpu->arch.mtrr_state.enabled = (data & 0xc00) >> 10;
> -	} else if (msr == MSR_MTRRfix64K_00000)
> +	if (msr == MSR_MTRRdefType)
> +		vcpu->arch.mtrr_state.deftype = data;
> +	else if (msr == MSR_MTRRfix64K_00000)
>  		p[0] = data;
>  	else if (msr == MSR_MTRRfix16K_80000 || msr == MSR_MTRRfix16K_A0000)
>  		p[1 + msr - MSR_MTRRfix16K_80000] = data;
> @@ -216,8 +214,7 @@ int kvm_mtrr_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
>  		return 1;
>  
>  	if (msr == MSR_MTRRdefType)
> -		*pdata = vcpu->arch.mtrr_state.def_type +
> -			 (vcpu->arch.mtrr_state.enabled << 10);
> +		*pdata = vcpu->arch.mtrr_state.deftype;
>  	else if (msr == MSR_MTRRfix64K_00000)
>  		*pdata = p[0];
>  	else if (msr == MSR_MTRRfix16K_80000 || msr == MSR_MTRRfix16K_A0000)
> @@ -256,14 +253,14 @@ static int get_mtrr_type(struct kvm_mtrr *mtrr_state,
>  	int i, num_var_ranges = KVM_NR_VAR_MTRR;
>  
>  	/* MTRR is completely disabled, use UC for all of physical memory. */
> -	if (!(mtrr_state->enabled & 0x2))
> +	if (!mtrr_state->mtrr_enabled)
>  		return MTRR_TYPE_UNCACHABLE;
>  
>  	/* Make end inclusive end, instead of exclusive */
>  	end--;
>  
>  	/* Look in fixed ranges. Just return the type as per start */
> -	if ((mtrr_state->enabled & 0x1) && (start < 0x100000)) {
> +	if (mtrr_state->fixed_mtrr_enabled && (start < 0x100000)) {
>  		int idx;
>  
>  		if (start < 0x80000) {
> 
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