linux-kernel - Re: [PATCH 2/7] KVM: SVM: Add VNMI bit definition

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Message-ID: <bd37180680b3e3ecec85b5151742092b9f1ce9ff.camel@redhat.com>
Date:   Tue, 07 Jun 2022 15:55:15 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Santosh Shukla <santosh.shukla@....com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] KVM: SVM: Add VNMI bit definition

On Thu, 2022-06-02 at 19:56 +0530, Santosh Shukla wrote:
> VNMI exposes 3 capability bits (V_NMI, V_NMI_MASK, and V_NMI_ENABLE) to
> virtualize NMI and NMI_MASK, Those capability bits are part of
> VMCB::intr_ctrl -
> V_NMI(11) - Indicates whether a virtual NMI is pending in the guest.
So this is like bit in IRR

> V_NMI_MASK(12) - Indicates whether virtual NMI is masked in the guest.
And that is like bit in ISR.

Question: what are the interactions with GIF/vGIF and this feature?

> V_NMI_ENABLE(26) - Enables the NMI virtualization feature for the guest.
> 
> When Hypervisor wants to inject NMI, it will set V_NMI bit, Processor
> will clear the V_NMI bit and Set the V_NMI_MASK which means the Guest is
> handling NMI, After the guest handled the NMI, The processor will clear
> the V_NMI_MASK on the successful completion of IRET instruction Or if
> VMEXIT occurs while delivering the virtual NMI.
> 
> To enable the VNMI capability, Hypervisor need to program
> V_NMI_ENABLE bit 1.
> 
> Signed-off-by: Santosh Shukla <santosh.shukla@....com>
> ---
>  arch/x86/include/asm/svm.h | 7 +++++++
>  arch/x86/kvm/svm/svm.c     | 6 ++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 1b07fba11704..22d918555df0 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -195,6 +195,13 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
>  #define AVIC_ENABLE_SHIFT 31
>  #define AVIC_ENABLE_MASK (1 << AVIC_ENABLE_SHIFT)
>  
> +#define V_NMI_PENDING_SHIFT 11
> +#define V_NMI_PENDING (1 << V_NMI_PENDING_SHIFT)
> +#define V_NMI_MASK_SHIFT 12
> +#define V_NMI_MASK (1 << V_NMI_MASK_SHIFT)
> +#define V_NMI_ENABLE_SHIFT 26
> +#define V_NMI_ENABLE (1 << V_NMI_ENABLE_SHIFT)
> +
>  #define LBR_CTL_ENABLE_MASK BIT_ULL(0)
>  #define VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK BIT_ULL(1)
>  
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 200045f71df0..860f28c668bd 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -198,6 +198,8 @@ module_param(dump_invalid_vmcb, bool, 0644);
>  bool intercept_smi = true;
>  module_param(intercept_smi, bool, 0444);
>  
> +static bool vnmi;
> +module_param(vnmi, bool, 0444);
>  
>  static bool svm_gp_erratum_intercept = true;
>  
> @@ -4930,6 +4932,10 @@ static __init int svm_hardware_setup(void)
>                 svm_x86_ops.vcpu_get_apicv_inhibit_reasons = NULL;
>         }
>  
> +       vnmi = vnmi && boot_cpu_has(X86_FEATURE_V_NMI);
> +       if (vnmi)
> +               pr_info("V_NMI enabled\n");
> +
>         if (vls) {
>                 if (!npt_enabled ||
>                     !boot_cpu_has(X86_FEATURE_V_VMSAVE_VMLOAD) ||


Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky