Re: [PATCH v6 6/9] KVM: nVMX: Use macros and #defines in vmx_restore_vmx_basic()

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 3/9/2024 9:27 AM, Sean Christopherson wrote:
> From: Xin Li <xin3.li@intel.com>
> 
> Use macros in vmx_restore_vmx_basic() 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@intel.com>
> Cc: Kai Huang <kai.huang@intel.com>
> Signed-off-by: Xin Li <xin3.li@intel.com>
> [sean: split to separate patch, write changelog, drop #defines]
> Signed-off-by: Sean Christopherson <seanjc@google.com>

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

> ---
>   arch/x86/kvm/vmx/nested.c | 25 ++++++++++++++++++-------
>   1 file changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 82a35aba7d2b..4ad8696c25af 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -1228,21 +1228,32 @@ static bool is_bitwise_subset(u64 superset, u64 subset, u64 mask)
>   
>   static int vmx_restore_vmx_basic(struct vcpu_vmx *vmx, u64 data)
>   {
> -	const u64 feature_and_reserved =
> -		/* feature (except bit 48; see below) */
> -		BIT_ULL(49) | BIT_ULL(54) | BIT_ULL(55) |
> -		/* reserved */
> -		BIT_ULL(31) | GENMASK_ULL(47, 45) | GENMASK_ULL(63, 56);
> +	const u64 feature_bits = VMX_BASIC_DUAL_MONITOR_TREATMENT |
> +				 VMX_BASIC_INOUT |
> +				 VMX_BASIC_TRUE_CTLS;
> +
> +	const u64 reserved_bits = GENMASK_ULL(63, 56) |
> +				  GENMASK_ULL(47, 45) |
> +				  BIT_ULL(31);
> +
>   	u64 vmx_basic = vmcs_config.nested.basic;
>   
> -	if (!is_bitwise_subset(vmx_basic, data, feature_and_reserved))
> +	BUILD_BUG_ON(feature_bits & reserved_bits);
> +
> +	/*
> +	 * Except for 32BIT_PHYS_ADDR_ONLY, which is an anti-feature bit (has
> +	 * inverted polarity), 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_basic, data, feature_bits | reserved_bits))
>   		return -EINVAL;
>   
>   	/*
>   	 * KVM does not emulate a version of VMX that constrains physical
>   	 * addresses of VMX structures (e.g. VMCS) to 32-bits.
>   	 */
> -	if (data & BIT_ULL(48))
> +	if (data & VMX_BASIC_32BIT_PHYS_ADDR_ONLY)
>   		return -EINVAL;
>   
>   	if (vmx_basic_vmcs_revision_id(vmx_basic) !=