linux-kernel - Re: [PATCH 03/26] KVM: x86: Snapshot MSR index in a local variable when processing lists

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Date:   Wed, 05 Feb 2020 15:31:51 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/26] KVM: x86: Snapshot MSR index in a local variable when processing lists

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Snapshot the MSR index when processing the virtualized and emulated MSR
> lists in kvm_init_msr_list() to improve code readability, particularly
> in the RTIT and PerfMon MSR checks.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/x86.c | 22 +++++++++++++---------
>  1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 24597526b5de..3d4a5326d84e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5214,7 +5214,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  static void kvm_init_msr_list(void)
>  {
>  	struct x86_pmu_capability x86_pmu;
> -	u32 dummy[2];
> +	u32 dummy[2], msr_index;
>  	unsigned i;
>  
>  	BUILD_BUG_ON_MSG(INTEL_PMC_MAX_FIXED != 4,
> @@ -5227,14 +5227,16 @@ static void kvm_init_msr_list(void)
>  	num_msr_based_features = 0;
>  
>  	for (i = 0; i < ARRAY_SIZE(msrs_to_save_all); i++) {
> -		if (rdmsr_safe(msrs_to_save_all[i], &dummy[0], &dummy[1]) < 0)
> +		msr_index = msrs_to_save_all[i];
> +
> +		if (rdmsr_safe(msr_index, &dummy[0], &dummy[1]) < 0)
>  			continue;
>  
>  		/*
>  		 * Even MSRs that are valid in the host may not be exposed
>  		 * to the guests in some cases.
>  		 */
> -		switch (msrs_to_save_all[i]) {
> +		switch (msr_index) {
>  		case MSR_IA32_BNDCFGS:
>  			if (!kvm_mpx_supported())
>  				continue;
> @@ -5262,17 +5264,17 @@ static void kvm_init_msr_list(void)
>  			break;
>  		case MSR_IA32_RTIT_ADDR0_A ... MSR_IA32_RTIT_ADDR3_B:
>  			if (!kvm_x86_ops->pt_supported() ||
> -				msrs_to_save_all[i] - MSR_IA32_RTIT_ADDR0_A >=
> +				msr_index - MSR_IA32_RTIT_ADDR0_A >=
>  				intel_pt_validate_hw_cap(PT_CAP_num_address_ranges) * 2)
>  				continue;
>  			break;
>  		case MSR_ARCH_PERFMON_PERFCTR0 ... MSR_ARCH_PERFMON_PERFCTR0 + 17:
> -			if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_PERFCTR0 >=
> +			if (msr_index - MSR_ARCH_PERFMON_PERFCTR0 >=
>  			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
>  				continue;
>  			break;
>  		case MSR_ARCH_PERFMON_EVENTSEL0 ... MSR_ARCH_PERFMON_EVENTSEL0 + 17:
> -			if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_EVENTSEL0 >=
> +			if (msr_index - MSR_ARCH_PERFMON_EVENTSEL0 >=
>  			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
>  				continue;
>  			break;
> @@ -5280,14 +5282,16 @@ static void kvm_init_msr_list(void)
>  			break;
>  		}
>  
> -		msrs_to_save[num_msrs_to_save++] = msrs_to_save_all[i];
> +		msrs_to_save[num_msrs_to_save++] = msr_index;
>  	}
>  
>  	for (i = 0; i < ARRAY_SIZE(emulated_msrs_all); i++) {
> -		if (!kvm_x86_ops->has_emulated_msr(emulated_msrs_all[i]))
> +		msr_index = emulated_msrs_all[i];
> +
> +		if (!kvm_x86_ops->has_emulated_msr(msr_index))
>  			continue;
>  
> -		emulated_msrs[num_emulated_msrs++] = emulated_msrs_all[i];
> +		emulated_msrs[num_emulated_msrs++] = msr_index;
>  	}
>  
>  	for (i = 0; i < ARRAY_SIZE(msr_based_features_all); i++) {

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly