linux-kernel - Re: [PATCH 49/61] KVM: x86: Override host CPUID results with kvm_cpu

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Date:   Mon, 24 Feb 2020 23:57:10 +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 49/61] KVM: x86: Override host CPUID results with kvm_cpu_caps

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

> Override CPUID entries with kvm_cpu_caps during KVM_GET_SUPPORTED_CPUID
> instead of masking the host CPUID result, which is redundant now that
> the host CPUID is incorporated into kvm_cpu_caps at runtime.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/cpuid.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 4416f2422321..871c0bd04e19 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -261,13 +261,13 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
>  	return r;
>  }
>  
> -static __always_inline void cpuid_entry_mask(struct kvm_cpuid_entry2 *entry,
> -					     enum cpuid_leafs leaf)
> +static __always_inline void cpuid_entry_override(struct kvm_cpuid_entry2 *entry,
> +						 enum cpuid_leafs leaf)
>  {
>  	u32 *reg = cpuid_entry_get_reg(entry, leaf * 32);
>  
>  	BUILD_BUG_ON(leaf > ARRAY_SIZE(kvm_cpu_caps));
> -	*reg &= kvm_cpu_caps[leaf];
> +	*reg = kvm_cpu_caps[leaf];
>  }
>  
>  static __always_inline void kvm_cpu_cap_mask(enum cpuid_leafs leaf, u32 mask)
> @@ -488,8 +488,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		entry->eax = min(entry->eax, 0x1fU);
>  		break;
>  	case 1:
> -		cpuid_entry_mask(entry, CPUID_1_EDX);
> -		cpuid_entry_mask(entry, CPUID_1_ECX);
> +		cpuid_entry_override(entry, CPUID_1_EDX);
> +		cpuid_entry_override(entry, CPUID_1_ECX);
>  		/* we support x2apic emulation even if host does not support
>  		 * it since we emulate x2apic in software */
>  		cpuid_entry_set(entry, X86_FEATURE_X2APIC);
> @@ -543,9 +543,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  	/* function 7 has additional index. */
>  	case 7:
>  		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);
> +		cpuid_entry_override(entry, CPUID_7_0_EBX);
> +		cpuid_entry_override(entry, CPUID_7_ECX);
> +		cpuid_entry_override(entry, CPUID_7_EDX);
>  
>  		/* TSC_ADJUST and ARCH_CAPABILITIES are emulated in software. */
>  		cpuid_entry_set(entry, X86_FEATURE_TSC_ADJUST);
> @@ -564,7 +564,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  			if (!entry)
>  				goto out;
>  
> -			cpuid_entry_mask(entry, CPUID_7_1_EAX);
> +			cpuid_entry_override(entry, CPUID_7_1_EAX);
>  			entry->ebx = 0;
>  			entry->ecx = 0;
>  			entry->edx = 0;
> @@ -630,7 +630,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		if (!entry)
>  			goto out;
>  
> -		cpuid_entry_mask(entry, CPUID_D_1_EAX);
> +		cpuid_entry_override(entry, CPUID_D_1_EAX);
>  		if (entry->eax & (F(XSAVES)|F(XSAVEC)))
>  			entry->ebx = xstate_required_size(supported_xcr0, true);
>  		else
> @@ -709,8 +709,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		entry->eax = min(entry->eax, 0x8000001f);
>  		break;
>  	case 0x80000001:
> -		cpuid_entry_mask(entry, CPUID_8000_0001_EDX);
> -		cpuid_entry_mask(entry, CPUID_8000_0001_ECX);
> +		cpuid_entry_override(entry, CPUID_8000_0001_EDX);
> +		cpuid_entry_override(entry, CPUID_8000_0001_ECX);
>  		break;
>  	case 0x80000007: /* Advanced power management */
>  		/* invariant TSC is CPUID.80000007H:EDX[8] */
> @@ -728,7 +728,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  			g_phys_as = phys_as;
>  		entry->eax = g_phys_as | (virt_as << 8);
>  		entry->edx = 0;
> -		cpuid_entry_mask(entry, CPUID_8000_0008_EBX);
> +		cpuid_entry_override(entry, CPUID_8000_0008_EBX);
>  		/*
>  		 * AMD has separate bits for each SPEC_CTRL bit.
>  		 * arch/x86/kernel/cpu/bugs.c is kind enough to
> @@ -770,7 +770,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		entry->eax = min(entry->eax, 0xC0000004);
>  		break;
>  	case 0xC0000001:
> -		cpuid_entry_mask(entry, CPUID_C000_0001_EDX);
> +		cpuid_entry_override(entry, CPUID_C000_0001_EDX);
>  		break;
>  	case 3: /* Processor serial number */
>  	case 5: /* MONITOR/MWAIT */

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

-- 
Vitaly