linux-kernel - Re: [PATCH 1/6] KVM: x86: Virtualize CR4.LASS

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Message-ID: <9e2a5232-0c74-585c-9f32-ff9cdd22883a@linux.intel.com>
Date:   Mon, 24 Apr 2023 14:45:31 +0800
From:   Binbin Wu <binbin.wu@...ux.intel.com>
To:     Zeng Guang <guang.zeng@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        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>, kvm@...r.kernel.org
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Gao Chao <chao.gao@...el.com>
Subject: Re: [PATCH 1/6] KVM: x86: Virtualize CR4.LASS

Reviewed-by: Binbin Wu <binbin.wu@...ux.intel.com>

one nit below

On 4/20/2023 9:37 PM, Zeng Guang wrote:
> Virtualize CR4.LASS[bit 27] under KVM control instead of being guest-owned
under control of KVM or under KVM's control

Or just simply use "intercept"?

> as CR4.LASS generally set once for each vCPU at boot time and won't be
> toggled at runtime. Besides, only if VM has LASS capability enumerated with
> CPUID.(EAX=07H.ECX=1):EAX.LASS[bit 6], KVM allows guest software to be able
> to set CR4.LASS. By design CR4.LASS can be manipulated by nested guest as
> well.
>
> Notes: Setting CR4.LASS to 1 enable LASS in IA-32e mode. It doesn't take
> effect in legacy mode even if CR4.LASS is set.
>
> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
> ---
>   arch/x86/include/asm/kvm_host.h | 2 +-
>   arch/x86/kvm/vmx/vmx.c          | 3 +++
>   arch/x86/kvm/x86.h              | 2 ++
>   3 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 6aaae18f1854..8ff89a52ef66 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -125,7 +125,7 @@
>   			  | X86_CR4_PGE | X86_CR4_PCE | X86_CR4_OSFXSR | X86_CR4_PCIDE \
>   			  | X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE \
>   			  | X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_VMXE \
> -			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP))
> +			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP | X86_CR4_LASS))
>   
>   #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
>   
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 43ff3276918b..c923d7599d71 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7569,6 +7569,9 @@ static void nested_vmx_cr_fixed1_bits_update(struct kvm_vcpu *vcpu)
>   	cr4_fixed1_update(X86_CR4_UMIP,       ecx, feature_bit(UMIP));
>   	cr4_fixed1_update(X86_CR4_LA57,       ecx, feature_bit(LA57));
>   
> +	entry = kvm_find_cpuid_entry_index(vcpu, 0x7, 1);
> +	cr4_fixed1_update(X86_CR4_LASS,       eax, feature_bit(LASS));
> +
>   #undef cr4_fixed1_update
>   }
>   
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 7c8a30d44c29..218f4c73789a 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -475,6 +475,8 @@ bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
>   		__reserved_bits |= X86_CR4_VMXE;        \
>   	if (!__cpu_has(__c, X86_FEATURE_PCID))          \
>   		__reserved_bits |= X86_CR4_PCIDE;       \
> +	if (!__cpu_has(__c, X86_FEATURE_LASS))          \
> +		__reserved_bits |= X86_CR4_LASS;        \
>   	__reserved_bits;                                \
>   })
>