On 7/23/2025 11:50 PM, Chao Gao wrote:
@@ -2578,6 +2588,17 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12) vmcs_writel(GUEST_IDTR_BASE, vmcs12->guest_idtr_base); vmx_segment_cache_clear(vmx); + + if (nested_cpu_load_guest_fred_states(vmcs12)) { + vmcs_write64(GUEST_IA32_FRED_CONFIG, vmcs12->guest_ia32_fred_config); + vmcs_write64(GUEST_IA32_FRED_RSP1, vmcs12->guest_ia32_fred_rsp1); + vmcs_write64(GUEST_IA32_FRED_RSP2, vmcs12->guest_ia32_fred_rsp2); + vmcs_write64(GUEST_IA32_FRED_RSP3, vmcs12->guest_ia32_fred_rsp3); + vmcs_write64(GUEST_IA32_FRED_STKLVLS, vmcs12->guest_ia32_fred_stklvls); + vmcs_write64(GUEST_IA32_FRED_SSP1, vmcs12->guest_ia32_fred_ssp1); + vmcs_write64(GUEST_IA32_FRED_SSP2, vmcs12->guest_ia32_fred_ssp2); + vmcs_write64(GUEST_IA32_FRED_SSP3, vmcs12->guest_ia32_fred_ssp3); + }I think we need to snapshot L1's FRED MSR values before nested VM entry and propagate them to GUEST_IA32_FRED* of VMCS02 for !nested_cpu_load_guest_fred_states(vmcs12) case. i.e., from guest's view, FRED MSRs shouldn't change across VM-entry if "Load guest FRED states" isn't set. Refer to the comment above 'pre_vmenter_debugctl' definition and also the CET implmenetation*. [*]: https://lore.kernel.org/kvm/20250704085027.182163-22-chao.gao@xxxxxxxxx/
Nice catch, it really took me a while to understand the issue.
