linux-kernel - Re: [PATCH 45/61] KVM: x86: Fold CPUID 0x7 masking back into __do_cpuid

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Message-ID: <87wo8bmxs4.fsf@vitty.brq.redhat.com>
Date:   Mon, 24 Feb 2020 23:21:47 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.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 45/61] KVM: x86: Fold CPUID 0x7 masking back into __do_cpuid_func()

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

> Move the CPUID 0x7 masking back into __do_cpuid_func() now that the
> size of the code has been trimmed down significantly.
>
> Tweak the WARN case, which is impossible to hit unless the CPU is
> completely broken, to break the loop before creating the bogus entry.
>
> Opportunustically reorder the cpuid_entry_set() calls and shorten the
> comment about emulation to further reduce the footprint of CPUID 0x7.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/cpuid.c | 62 ++++++++++++++++----------------------------
>  1 file changed, 22 insertions(+), 40 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 77a6c1db138d..7362e5238799 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -456,44 +456,6 @@ static int __do_cpuid_func_emulated(struct kvm_cpuid_array *array, u32 func)
>  	return 0;
>  }
>  
> -static inline void do_cpuid_7_mask(struct kvm_cpuid_entry2 *entry)
> -{
> -	switch (entry->index) {
> -	case 0:
> -		entry->eax = min(entry->eax, 1u);
> -		cpuid_entry_mask(entry, CPUID_7_0_EBX);
> -		/* TSC_ADJUST is emulated */
> -		cpuid_entry_set(entry, X86_FEATURE_TSC_ADJUST);
> -		cpuid_entry_mask(entry, CPUID_7_ECX);
> -		cpuid_entry_mask(entry, CPUID_7_EDX);
> -		if (boot_cpu_has(X86_FEATURE_IBPB) && boot_cpu_has(X86_FEATURE_IBRS))
> -			cpuid_entry_set(entry, X86_FEATURE_SPEC_CTRL);
> -		if (boot_cpu_has(X86_FEATURE_STIBP))
> -			cpuid_entry_set(entry, X86_FEATURE_INTEL_STIBP);
> -		if (boot_cpu_has(X86_FEATURE_AMD_SSBD))
> -			cpuid_entry_set(entry, X86_FEATURE_SPEC_CTRL_SSBD);
> -		/*
> -		 * We emulate ARCH_CAPABILITIES in software even
> -		 * if the host doesn't support it.
> -		 */
> -		cpuid_entry_set(entry, X86_FEATURE_ARCH_CAPABILITIES);
> -		break;
> -	case 1:
> -		cpuid_entry_mask(entry, CPUID_7_1_EAX);
> -		entry->ebx = 0;
> -		entry->ecx = 0;
> -		entry->edx = 0;
> -		break;
> -	default:
> -		WARN_ON_ONCE(1);
> -		entry->eax = 0;
> -		entry->ebx = 0;
> -		entry->ecx = 0;
> -		entry->edx = 0;
> -		break;
> -	}
> -}
> -
>  static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  {
>  	struct kvm_cpuid_entry2 *entry;
> @@ -555,14 +517,34 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		break;
>  	/* function 7 has additional index. */
>  	case 7:
> -		do_cpuid_7_mask(entry);
> +		entry->eax = min(entry->eax, 1u);
> +		cpuid_entry_mask(entry, CPUID_7_0_EBX);
> +		cpuid_entry_mask(entry, CPUID_7_ECX);
> +		cpuid_entry_mask(entry, CPUID_7_EDX);
> +
> +		/* TSC_ADJUST and ARCH_CAPABILITIES are emulated in software. */
> +		cpuid_entry_set(entry, X86_FEATURE_TSC_ADJUST);
> +		cpuid_entry_set(entry, X86_FEATURE_ARCH_CAPABILITIES);
> +
> +		if (boot_cpu_has(X86_FEATURE_IBPB) && boot_cpu_has(X86_FEATURE_IBRS))
> +			cpuid_entry_set(entry, X86_FEATURE_SPEC_CTRL);
> +		if (boot_cpu_has(X86_FEATURE_STIBP))
> +			cpuid_entry_set(entry, X86_FEATURE_INTEL_STIBP);
> +		if (boot_cpu_has(X86_FEATURE_AMD_SSBD))
> +			cpuid_entry_set(entry, X86_FEATURE_SPEC_CTRL_SSBD);
>  
>  		for (i = 1, max_idx = entry->eax; i <= max_idx; i++) {
> +			if (WARN_ON_ONCE(i > 1))
> +				break;
> +
>  			entry = do_host_cpuid(array, function, i);
>  			if (!entry)
>  				goto out;
>  
> -			do_cpuid_7_mask(entry);
> +			cpuid_entry_mask(entry, CPUID_7_1_EAX);
> +			entry->ebx = 0;
> +			entry->ecx = 0;
> +			entry->edx = 0;
>  		}
>  		break;
>  	case 9:

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

-- 
Vitaly