linux-kernel - Re: [PATCH v12 20/24] KVM: x86: Enable CET virtualization for VMX and advertise to userspace

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Message-ID: <aKTHRKKr4C-c2LZy@google.com>
Date: Tue, 19 Aug 2025 11:49:40 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, mlevitsk@...hat.com, 
	rick.p.edgecombe@...el.com, weijiang.yang@...el.com, xin@...or.com, 
	Mathias Krause <minipli@...ecurity.net>, John Allen <john.allen@....com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v12 20/24] KVM: x86: Enable CET virtualization for VMX and
 advertise to userspace

On Mon, Aug 11, 2025, Chao Gao wrote:
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index ce10a7e2d3d9..c85c50019523 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -134,6 +134,7 @@
>  #define VMX_BASIC_DUAL_MONITOR_TREATMENT	BIT_ULL(49)
>  #define VMX_BASIC_INOUT				BIT_ULL(54)
>  #define VMX_BASIC_TRUE_CTLS			BIT_ULL(55)
> +#define VMX_BASIC_NO_HW_ERROR_CODE_CC		BIT_ULL(56)
>  
>  static inline u32 vmx_basic_vmcs_revision_id(u64 vmx_basic)
>  {
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 85079caaf507..2515b2623fb1 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -944,6 +944,7 @@ void kvm_set_cpu_caps(void)
>  		VENDOR_F(WAITPKG),
>  		F(SGX_LC),
>  		F(BUS_LOCK_DETECT),
> +		F(SHSTK),

I think we should limit this to 64-bit kernels with X86_64_F().  It probably
won't change anything in practice, but we mitigate the virtualization holes related
to 32-bit vCPUs at least a little bit.

>  	);
>  
>  	/*
> @@ -970,6 +971,7 @@ void kvm_set_cpu_caps(void)
>  		F(AMX_INT8),
>  		F(AMX_BF16),
>  		F(FLUSH_L1D),
> +		F(IBT),
>  	);
>