linux-kernel - Re: [PATCH v3 6/7] KVM: x86: SVM: allow to force AVIC to be enabled

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Date:   Wed, 9 Mar 2022 14:41:59 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jim Mattson <jmattson@...gle.com>, x86@...nel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH v3 6/7] KVM: x86: SVM: allow to force AVIC to be enabled

On 3/1/22 15:36, Maxim Levitsky wrote:
> Apparently on some systems AVIC is disabled in CPUID but still usable.
> 
> Allow the user to override the CPUID if the user is willing to
> take the risk.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---
>   arch/x86/kvm/svm/svm.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 776585dd77769..a26b4c899899e 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -202,6 +202,9 @@ module_param(tsc_scaling, int, 0444);
>   static bool avic;
>   module_param(avic, bool, 0444);
>   
> +static bool force_avic;
> +module_param_unsafe(force_avic, bool, 0444);
> +
>   bool __read_mostly dump_invalid_vmcb;
>   module_param(dump_invalid_vmcb, bool, 0644);
>   
> @@ -4896,10 +4899,14 @@ static __init int svm_hardware_setup(void)
>   			nrips = false;
>   	}
>   
> -	enable_apicv = avic = avic && npt_enabled && boot_cpu_has(X86_FEATURE_AVIC);
> +	enable_apicv = avic = avic && npt_enabled && (boot_cpu_has(X86_FEATURE_AVIC) || force_avic);
>   
>   	if (enable_apicv) {
> -		pr_info("AVIC enabled\n");
> +		if (!boot_cpu_has(X86_FEATURE_AVIC)) {
> +			pr_warn("AVIC is not supported in CPUID but force enabled");
> +			pr_warn("Your system might crash and burn");
> +		} else
> +			pr_info("AVIC enabled\n");
>   
>   		amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
>   	} else {

Queued, thanks.

Paolo