Re: [PATCH v4 21/25] KVM: VMX: Move LOAD_IA32_PERF_GLOBAL_CTRL errata handling out of setup_vmcs_config()

Paolo Bonzini
2022-07-28T22:25:24Z

On 7/22/22 00:56, Sean Christopherson wrote:
> Except the errata are based on FMS and the FMS exposed to the L1 hypervisor may
> not be the real FMS.
>
> But that's moot, because they_should_ be fully emulated by KVM anyways; KVM
> runs L2 with a MSR value modified by perf, not the raw MSR value requested by L1.
>
> Of course KVM screws things up and fails to clear the flag in entry controls...
> All exit controls are emulated so at least KVM gets those right.

Can you send this as a separate patch?

Paolo

> Untested, but I believe KVM the fix is:
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index d0e781c7ac72..76926147b672 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2357,7 +2357,8 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0
> * we can avoid VMWrites during vmx_set_efer().
> */
> exec_control = __vm_entry_controls_get(vmcs01);
> - exec_control |= vmcs12->vm_entry_controls;
> + exec_control |= (vmcs12->vm_entry_controls &
> + ~VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL);
> exec_control &= ~(VM_ENTRY_IA32E_MODE | VM_ENTRY_LOAD_IA32_EFER);
> if (cpu_has_load_ia32_efer()) {
> if (guest_efer & EFER_LMA)