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

Xiaoyao Li
2024-04-01T07:00:42Z

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) !=