linux-kernel - Re: [PATCH v2 3/3] x86/cpu, KVM: Use helper function to read MSR_IA32_ARCH

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Message-ID: <e5c0fd8d-00fd-8285-3066-1a7bf6e17429@intel.com>
Date:   Wed, 24 May 2023 16:19:38 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Chao Gao <chao.gao@...el.com>, kvm@...r.kernel.org, x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kim Phillips <kim.phillips@....com>,
        Juergen Gross <jgross@...e.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] x86/cpu, KVM: Use helper function to read
 MSR_IA32_ARCH_CAPABILITIES

On 5/24/2023 2:16 PM, Chao Gao wrote:
> KVM open-codes x86_read_arch_cap_msr() in a few places. Eliminate them
> by exposing the helper function and using it directly.
> 
> No functional change intended.
> 

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

> Signed-off-by: Chao Gao <chao.gao@...el.com>
> ---
>   arch/x86/kernel/cpu/common.c |  1 +
>   arch/x86/kvm/vmx/vmx.c       | 19 +++++--------------
>   arch/x86/kvm/x86.c           |  7 +------
>   3 files changed, 7 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 80710a68ef7d..b34dd3f3e6c4 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1315,6 +1315,7 @@ u64 x86_read_arch_cap_msr(void)
>   
>   	return ia32_cap;
>   }
> +EXPORT_SYMBOL_GPL(x86_read_arch_cap_msr);
>   
>   static bool arch_cap_mmio_immune(u64 ia32_cap)
>   {
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 8274ef5e89e5..3dec4a4f637e 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -255,14 +255,9 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
>   		return 0;
>   	}
>   
> -	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES)) {
> -		u64 msr;
> -
> -		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, msr);
> -		if (msr & ARCH_CAP_SKIP_VMENTRY_L1DFLUSH) {
> -			l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
> -			return 0;
> -		}
> +	if (x86_read_arch_cap_msr() & ARCH_CAP_SKIP_VMENTRY_L1DFLUSH) {
> +		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
> +		return 0;
>   	}
>   
>   	/* If set to auto use the default l1tf mitigation method */
> @@ -394,13 +389,9 @@ static int vmentry_l1d_flush_get(char *s, const struct kernel_param *kp)
>   
>   static void vmx_setup_fb_clear_ctrl(void)
>   {
> -	u64 msr;
> -
> -	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES) &&
> -	    !boot_cpu_has_bug(X86_BUG_MDS) &&
> +	if (!boot_cpu_has_bug(X86_BUG_MDS) &&
>   	    !boot_cpu_has_bug(X86_BUG_TAA)) {
> -		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, msr);
> -		if (msr & ARCH_CAP_FB_CLEAR_CTRL)
> +		if (x86_read_arch_cap_msr() & ARCH_CAP_FB_CLEAR_CTRL)
>   			vmx_fb_clear_ctrl_available = true;
>   	}
>   }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f7838260c183..b1bdb84ac10f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1612,12 +1612,7 @@ static bool kvm_is_immutable_feature_msr(u32 msr)
>   
>   static u64 kvm_get_arch_capabilities(void)
>   {
> -	u64 data = 0;
> -
> -	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES)) {
> -		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, data);
> -		data &= KVM_SUPPORTED_ARCH_CAP;
> -	}
> +	u64 data = x86_read_arch_cap_msr() & KVM_SUPPORTED_ARCH_CAP;
>   
>   	/*
>   	 * If nx_huge_pages is enabled, KVM's shadow paging will ensure that