linux-kernel - Re: [PATCH v2 14/28] KVM: VMX: Check VM_ENTRY_IA32E_MODE in setup_vmcs

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Message-ID: <CALMp9eRZAJ3srAtEXFy2nZ4ms9xPz=Zqi6B=tXo9_kHRLvoAMg@mail.gmail.com>
Date:   Wed, 29 Jun 2022 13:28:22 -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 14/28] KVM: VMX: Check VM_ENTRY_IA32E_MODE in setup_vmcs_config()

On Wed, Jun 29, 2022 at 8:07 AM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
> VM_ENTRY_IA32E_MODE control is toggled dynamically by vmx_set_efer()
> and setup_vmcs_config() doesn't check its existence. On the contrary,
> nested_vmx_setup_ctls_msrs() doesn set it on x86_64. Add the missing
> check and filter the bit out in vmx_vmentry_ctrl().
>
> No (real) functional change intended as all existing CPUs supporting
> long mode and VMX are supposed to have it.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 83feb70d44a9..da8bbba38d0e 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2610,6 +2610,9 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>                 _pin_based_exec_control &= ~PIN_BASED_POSTED_INTR;
>
>         min = VM_ENTRY_LOAD_DEBUG_CONTROLS;
> +#ifdef CONFIG_X86_64
> +       min |= VM_ENTRY_IA32E_MODE;
> +#endif
>         opt = VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL |
>               VM_ENTRY_LOAD_IA32_PAT |
>               VM_ENTRY_LOAD_IA32_EFER |
> @@ -4242,9 +4245,15 @@ static u32 vmx_vmentry_ctrl(void)
>         if (vmx_pt_mode_is_system())
>                 vmentry_ctrl &= ~(VM_ENTRY_PT_CONCEAL_PIP |
>                                   VM_ENTRY_LOAD_IA32_RTIT_CTL);
> -       /* Loading of EFER and PERF_GLOBAL_CTRL are toggled dynamically */
> -       return vmentry_ctrl &
> -               ~(VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL | VM_ENTRY_LOAD_IA32_EFER);
> +       /*
> +        * Loading of EFER, VM_ENTRY_IA32E_MODE, and PERF_GLOBAL_CTRL
> +        * are toggled dynamically.
> +        */
Nit: Previously, this could be read as "loading of (EFER and
PERF_GLOBAL_CTRL)." Since "loading" doesn't apply to IA32e mode,
you've lost "loading" of PERF_GLOBAL_CONTROL. Also, why drop the
VM_ENTRY prefix from the MSRs and not from IA32e mode?
Perhaps:

/*
 * IA32e mode, and loading of EFER and PERF_GLOBAL_CTRL are toggled dynamically.
 */

> +       vmentry_ctrl &= ~(VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL |
> +                         VM_ENTRY_LOAD_IA32_EFER |
> +                         VM_ENTRY_IA32E_MODE);
> +
> +       return vmentry_ctrl;
>  }
>
>  static u32 vmx_vmexit_ctrl(void)
> --
> 2.35.3
>
Reviewed-by: Jim Mattson <jmattson@...gle.com>