Re: [PATCH v6 9/9] KVM: nVMX: Use macros and #defines in vmx_restore_vmx_misc()

[Xiaoyao Li]

On 3/9/2024 9:27 AM, Sean Christopherson wrote:
> From: Xin Li <xin3.li@xxxxxxxxx>
>
> Use macros in vmx_restore_vmx_misc() instead of open coding everything
> using BIT_ULL() and GENMASK_ULL().  Opportunistically split feature bits
> and reserved bits into separate variables, and add a comment explaining
> the subset logic (it's not immediately obvious that the set of feature
> bits is NOT the set of _supported_ feature bits).
>
> Cc: Shan Kang <shan.kang@xxxxxxxxx>
> Cc: Kai Huang <kai.huang@xxxxxxxxx>
> Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
> [sean: split to separate patch, write changelog, drop #defines]
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>

> ---
>   arch/x86/kvm/vmx/nested.c | 27 ++++++++++++++++++++-------
>   1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 06512ee7a5c4..6610d258c680 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -1322,16 +1322,29 @@ vmx_restore_control_msr(struct vcpu_vmx *vmx, u32 msr_index, u64 data)
>   
>   static int vmx_restore_vmx_misc(struct vcpu_vmx *vmx, u64 data)
>   {
> -	const u64 feature_and_reserved_bits =
> -		/* feature */
> -		BIT_ULL(5) | GENMASK_ULL(8, 6) | BIT_ULL(14) | BIT_ULL(15) |
> -		BIT_ULL(28) | BIT_ULL(29) | BIT_ULL(30) |
> -		/* reserved */
> -		GENMASK_ULL(13, 9) | BIT_ULL(31);
> +	const u64 feature_bits = VMX_MISC_SAVE_EFER_LMA |
> +				 VMX_MISC_ACTIVITY_HLT |
> +				 VMX_MISC_ACTIVITY_SHUTDOWN |
> +				 VMX_MISC_ACTIVITY_WAIT_SIPI |
> +				 VMX_MISC_INTEL_PT |
> +				 VMX_MISC_RDMSR_IN_SMM |
> +				 VMX_MISC_VMWRITE_SHADOW_RO_FIELDS |
> +				 VMX_MISC_VMXOFF_BLOCK_SMI |
> +				 VMX_MISC_ZERO_LEN_INS;
> +
> +	const u64 reserved_bits = BIT_ULL(31) | GENMASK_ULL(13, 9);
> +
>   	u64 vmx_misc = vmx_control_msr(vmcs_config.nested.misc_low,
>   				       vmcs_config.nested.misc_high);
>   
> -	if (!is_bitwise_subset(vmx_misc, data, feature_and_reserved_bits))
> +	BUILD_BUG_ON(feature_bits & reserved_bits);
> +
> +	/*
> +	 * The incoming value must not set feature bits or reserved bits that
> +	 * aren't allowed/supported by KVM.  Fields, i.e. multi-bit values, are
> +	 * explicitly checked below.
> +	 */
> +	if (!is_bitwise_subset(vmx_misc, data, feature_bits | reserved_bits))
>   		return -EINVAL;
>   
>   	if ((vmx->nested.msrs.pinbased_ctls_high &