linux-kernel - Re: [PATCH v4 21/25] KVM: VMX: Move LOAD_IA32_PERF_GLOBAL_CTRL errata handling out of setup_vmcs

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Date:   Fri, 29 Jul 2022 00:25:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 21/25] KVM: VMX: Move LOAD_IA32_PERF_GLOBAL_CTRL errata
 handling out of setup_vmcs_config()

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)