linux-kernel - Re: [PATCH v2 16/28] KVM: VMX: Tweak the special handling of SECONDARY_EXEC_ENCLS_EXITING in setup_vmcs

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Message-ID: <CALMp9eS_iAijAk4pdK1tjLbRp3XH-PhR1mX4gaSXztWPXJpfkA@mail.gmail.com>
Date:   Wed, 29 Jun 2022 11:56:38 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 16/28] KVM: VMX: Tweak the special handling of
 SECONDARY_EXEC_ENCLS_EXITING in setup_vmcs_config()

On Wed, Jun 29, 2022 at 8:07 AM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
> SECONDARY_EXEC_ENCLS_EXITING is conditionally added to the 'optional'
> checklist in setup_vmcs_config() but there's little value in doing so.
> First, as the control is optional, we can always check for its
> presence, no harm done. Second, the only real value cpu_has_sgx() check
> gives is that on the CPUs which support SECONDARY_EXEC_ENCLS_EXITING but
> don't support SGX, the control is not getting enabled. It's highly unlikely
> such CPUs exist but it's possible that some hypervisors expose broken vCPU
> models.
>
> Preserve cpu_has_sgx() check but filter the result of adjust_vmx_controls()
> instead of the input.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 89a3bbafa5af..e32d91006b80 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2528,9 +2528,9 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>                         SECONDARY_EXEC_PT_CONCEAL_VMX |
>                         SECONDARY_EXEC_ENABLE_VMFUNC |
>                         SECONDARY_EXEC_BUS_LOCK_DETECTION |
> -                       SECONDARY_EXEC_NOTIFY_VM_EXITING;
> -               if (cpu_has_sgx())
> -                       opt2 |= SECONDARY_EXEC_ENCLS_EXITING;
> +                       SECONDARY_EXEC_NOTIFY_VM_EXITING |
> +                       SECONDARY_EXEC_ENCLS_EXITING;
> +
>                 if (adjust_vmx_controls(min2, opt2,
>                                         MSR_IA32_VMX_PROCBASED_CTLS2,
>                                         &_cpu_based_2nd_exec_control) < 0)
> @@ -2577,6 +2577,9 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>                 vmx_cap->vpid = 0;
>         }
>
> +       if (!cpu_has_sgx())
> +               _cpu_based_2nd_exec_control &= ~SECONDARY_EXEC_ENCLS_EXITING;

NYC, but why is there a leading underscore here?

>         if (_cpu_based_exec_control & CPU_BASED_ACTIVATE_TERTIARY_CONTROLS) {
>                 u64 opt3 = TERTIARY_EXEC_IPI_VIRT;
>
> --
> 2.35.3
>
Reviewed-by: Jim Mattson <jmattson@...gle.com>