linux-kernel - Re: [PATCH] KVM: x86: optimize check for valid PAT value

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Date:   Wed, 10 Apr 2019 16:36:36 -0700
From:   Krish Sadhukhan <krish.sadhukhan@...cle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: optimize check for valid PAT value



On 04/10/2019 02:55 AM, Paolo Bonzini wrote:
> This check will soon be done on every nested vmentry and vmexit,
> "parallelize" it using bitwise operations.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>   arch/x86/kvm/mtrr.c    | 10 +---------
>   arch/x86/kvm/vmx/vmx.c |  2 +-
>   arch/x86/kvm/x86.h     |  8 ++++++++
>   3 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
> index e9ea2d45ae66..9f72cc427158 100644
> --- a/arch/x86/kvm/mtrr.c
> +++ b/arch/x86/kvm/mtrr.c
> @@ -48,11 +48,6 @@ static bool msr_mtrr_valid(unsigned msr)
>   	return false;
>   }
>   
> -static bool valid_pat_type(unsigned t)
> -{
> -	return t < 8 && (1 << t) & 0xf3; /* 0, 1, 4, 5, 6, 7 */
> -}
> -
>   static bool valid_mtrr_type(unsigned t)
>   {
>   	return t < 8 && (1 << t) & 0x73; /* 0, 1, 4, 5, 6 */
> @@ -67,10 +62,7 @@ bool kvm_mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>   		return false;
>   
>   	if (msr == MSR_IA32_CR_PAT) {
> -		for (i = 0; i < 8; i++)
> -			if (!valid_pat_type((data >> (i * 8)) & 0xff))
> -				return false;
> -		return true;
> +		return kvm_pat_valid(data);
>   	} else if (msr == MSR_MTRRdefType) {
>   		if (data & ~0xcff)
>   			return false;
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b6c533afbf27..b74679732cfc 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1891,7 +1891,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		break;
>   	case MSR_IA32_CR_PAT:
>   		if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
> -			if (!kvm_mtrr_valid(vcpu, MSR_IA32_CR_PAT, data))
> +			if (!kvm_pat_valid(data))
>   				return 1;
>   			vmcs_write64(GUEST_IA32_PAT, data);
>   			vcpu->arch.pat = data;
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 28406aa1136d..7bc7ac9d2a44 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -347,4 +347,12 @@ static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu)
>   	__this_cpu_write(current_vcpu, NULL);
>   }
>   
> +static inline bool kvm_pat_valid(u64 data)
> +{
> +	if (data & 0xF8F8F8F8F8F8F8F8)
> +		return false;
> +	/* 0, 1, 4, 5, 6, 7 are valid values.  */
> +	return (data | ((data & 0x0202020202020202) << 1)) == data;
> +}
> +
>   #endif

Reviewed-by: Krish Sadhukhan <krish.sadhukhan@...cle.com>