On Fri, Mar 28, 2025, Xin Li (Intel) wrote:
> From: Xin Li <xin3.li@intel.com>
>
> Do not virtualize FRED if FRED consistency checks fail.
>
> Either on broken hardware, or when run KVM on top of another hypervisor
> before the underlying hypervisor implements nested FRED correctly.
>
> Suggested-by: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Xin Li <xin3.li@intel.com>
> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
> Tested-by: Shan Kang <shan.kang@intel.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
> ---
>
> Change in v4:
> * Call out the reason why not check FRED VM-exit controls in
> cpu_has_vmx_fred() (Chao Gao).
> ---
> arch/x86/kvm/vmx/capabilities.h | 11 +++++++++++
> arch/x86/kvm/vmx/vmx.c | 3 +++
> 2 files changed, 14 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index b2aefee59395..b4f49a4690ca 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -400,6 +400,17 @@ static inline bool vmx_pebs_supported(void)
> return boot_cpu_has(X86_FEATURE_PEBS) && kvm_pmu_cap.pebs_ept;
> }
>
> +static inline bool cpu_has_vmx_fred(void)
> +{
> + /*
> + * setup_vmcs_config() guarantees FRED VM-entry/exit controls
> + * are either all set or none. So, no need to check FRED VM-exit
> + * controls.
> + */
> + return cpu_feature_enabled(X86_FEATURE_FRED) &&
Drop the cpu_feature_enabled(). These helpers are all about checking raw CPU
support; whether or not the kernel is configured to support FRED is irrelevant.
[For these helpers; KVM obviously needs to account for FRED support in other
paths, but that should be automagically handled by kvm_set_cpu_caps()]
> + (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_FRED);
> +}
> +
> static inline bool cpu_has_notify_vmexit(void)
> {
> return vmcs_config.cpu_based_2nd_exec_ctrl &
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index e38545d0dd17..ab84939ace96 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -8052,6 +8052,9 @@ static __init void vmx_set_cpu_caps(void)
> kvm_cpu_cap_check_and_set(X86_FEATURE_DTES64);
> }
>
> + if (!cpu_has_vmx_fred())
> + kvm_cpu_cap_clear(X86_FEATURE_FRED);
> +
> if (!enable_pmu)
> kvm_cpu_cap_clear(X86_FEATURE_PDCM);
> kvm_caps.supported_perf_cap = vmx_get_perf_capabilities();
> --
> 2.48.1
>