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SubjectRe: [PATCH 1/6] KVM: x86: Virtualize CR4.LASS
From
Reviewed-by: Binbin Wu <binbin.wu@linux.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@intel.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; \
> })
>

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