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

[Chao Gao]

On Thu, Apr 20, 2023 at 09:37:19PM +0800, Zeng Guang wrote:
>Virtualize CR4.LASS[bit 27] under KVM control instead of being guest-owned
>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.

This is inaccurate. The change in nested_vmx_cr_fixed1_bits_update() is
to allow L1 guests to set CR4.LASS in VMX operation. I would say:

Set the CR4.LASS bit in the emulated IA32_VMX_CR4_FIXED1 MSR for guests
to allow guests to enable LASS in nested VMX operation.