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

[Zeng Guang]

On 4/24/2023 2:45 PM, Binbin Wu wrote:
> Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
>
> 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"?

OK. Will change it.

> > 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@xxxxxxxxx>
> > ---
> >    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;                                \
> >    })
> >