linux-kernel - Re: [PATCH 09/15] KVM: VMX: Use flag to indicate "active" uret MSRs instead of sorting list

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Date:   Fri, 7 May 2021 20:31:53 -0700
From:   Reiji Watanabe <reijiw@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 09/15] KVM: VMX: Use flag to indicate "active" uret MSRs
 instead of sorting list

> -static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr)
> +static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr,
> +                              bool load_into_hardware)
>  {
> -       struct vmx_uret_msr tmp;
> -       int from, to;
> +       struct vmx_uret_msr *uret_msr;
>
> -       from = __vmx_find_uret_msr(vmx, msr);
> -       if (from < 0)
> +       uret_msr = vmx_find_uret_msr(vmx, msr);
> +       if (!uret_msr)
>                 return;
> -       to = vmx->nr_active_uret_msrs++;
>
> -       tmp = vmx->guest_uret_msrs[to];
> -       vmx->guest_uret_msrs[to] = vmx->guest_uret_msrs[from];
> -       vmx->guest_uret_msrs[from] = tmp;
> +       uret_msr->load_into_hardware = load_into_hardware;
>  }
>
>  /*
> @@ -1785,30 +1781,36 @@ static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr)
>   */
>  static void setup_msrs(struct vcpu_vmx *vmx)
>  {
> -       vmx->guest_uret_msrs_loaded = false;
> -       vmx->nr_active_uret_msrs = 0;
>  #ifdef CONFIG_X86_64
> +       bool load_syscall_msrs;
> +
>         /*
>          * The SYSCALL MSRs are only needed on long mode guests, and only
>          * when EFER.SCE is set.
>          */
> -       if (is_long_mode(&vmx->vcpu) && (vmx->vcpu.arch.efer & EFER_SCE)) {
> -               vmx_setup_uret_msr(vmx, MSR_STAR);
> -               vmx_setup_uret_msr(vmx, MSR_LSTAR);
> -               vmx_setup_uret_msr(vmx, MSR_SYSCALL_MASK);
> -       }
> +       load_syscall_msrs = is_long_mode(&vmx->vcpu) &&
> +                           (vmx->vcpu.arch.efer & EFER_SCE);
> +
> +       vmx_setup_uret_msr(vmx, MSR_STAR, load_syscall_msrs);
> +       vmx_setup_uret_msr(vmx, MSR_LSTAR, load_syscall_msrs);
> +       vmx_setup_uret_msr(vmx, MSR_SYSCALL_MASK, load_syscall_msrs);
>  #endif
> -       if (update_transition_efer(vmx))
> -               vmx_setup_uret_msr(vmx, MSR_EFER);
> +       vmx_setup_uret_msr(vmx, MSR_EFER, update_transition_efer(vmx));
>
> -       if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP)  ||
> -           guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDPID))
> -               vmx_setup_uret_msr(vmx, MSR_TSC_AUX);
> +       vmx_setup_uret_msr(vmx, MSR_TSC_AUX,
> +                          guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP) ||
> +                          guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDPID));

Shouldn't vmx_setup_uret_msr(,MSR_TSC_AUX,) be called to update
the new flag load_into_hardware for MSR_TSC_AUX when CPUID
(X86_FEATURE_RDTSCP/X86_FEATURE_RDPID) of the vCPU is updated ?


Thanks,
Reiji