Messages in this thread | | | Date | Tue, 25 Apr 2023 10:35:25 +0800 | Subject | Re: [PATCH 1/6] KVM: x86: Virtualize CR4.LASS | From | Zeng Guang <> |
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On 4/24/2023 3:32 PM, Gao, Chao wrote: > 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.
Essentially it allows nested guest to set CR4.LASS. L1 guest uses cr4_fixed1 to check cr4 value requested to set by nested guest valid or not. Nested guest will get #GP fault if it's not allowed.
> 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.
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