linux-kernel - Re: [PATCH 6/7] KVM: SVM: hyper-v: Enlightened MSR-Bitmap support

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Message-ID: <87czv5aun1.fsf@vitty.brq.redhat.com>
Date:   Thu, 08 Apr 2021 13:22:10 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Vineeth Pillai <viremana@...ux.microsoft.com>,
        Lan Tianyu <Tianyu.Lan@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Wei Liu <wei.liu@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>
Cc:     Vineeth Pillai <viremana@...ux.microsoft.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "K. Y. Srinivasan" <kys@...rosoft.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Subject: Re: [PATCH 6/7] KVM: SVM: hyper-v: Enlightened MSR-Bitmap support

Vineeth Pillai <viremana@...ux.microsoft.com> writes:

> Enlightened MSR-Bitmap as per TLFS:
>
>  "The L1 hypervisor may collaborate with the L0 hypervisor to make MSR
>   accesses more efficient. It can enable enlightened MSR bitmaps by setting
>   the corresponding field in the enlightened VMCS to 1. When enabled, L0
>   hypervisor does not monitor the MSR bitmaps for changes. Instead, the L1
>   hypervisor must invalidate the corresponding clean field after making
>   changes to one of the MSR bitmaps."
>
> Enable this for SVM.
>
> Related VMX changes:
> commit ceef7d10dfb6 ("KVM: x86: VMX: hyper-v: Enlightened MSR-Bitmap support")
>
> Signed-off-by: Vineeth Pillai <viremana@...ux.microsoft.com>
> ---
>  arch/x86/kvm/svm/svm.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 6287cab61f15..3562a247b7e8 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -646,6 +646,27 @@ static bool msr_write_intercepted(struct kvm_vcpu *vcpu, u32 msr)
>  	return !!test_bit(bit_write,  &tmp);
>  }
>  
> +#if IS_ENABLED(CONFIG_HYPERV)
> +static inline void hv_vmcb_dirty_nested_enlightenments(struct kvm_vcpu *vcpu)
> +{
> +	struct vmcb *vmcb = to_svm(vcpu)->vmcb;
> +
> +	/*
> +	 * vmcb can be NULL if called during early vcpu init.
> +	 * And its okay not to mark vmcb dirty during vcpu init
> +	 * as we mark it dirty unconditionally towards end of vcpu
> +	 * init phase.
> +	 */
> +	if (vmcb && vmcb_is_clean(vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS) &&
> +	    vmcb->hv_enlightenments.hv_enlightenments_control.msr_bitmap)
> +		vmcb_mark_dirty(vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS);

vmcb_is_clean() check seems to be superfluous, vmcb_mark_dirty() does no
harm if the bit was already cleared.

> +}
> +#else
> +static inline void hv_vmcb_dirty_nested_enlightenments(struct kvm_vcpu *vcpu)
> +{
> +}
> +#endif
> +
>  static void set_msr_interception_bitmap(struct kvm_vcpu *vcpu, u32 *msrpm,
>  					u32 msr, int read, int write)
>  {
> @@ -677,6 +698,9 @@ static void set_msr_interception_bitmap(struct kvm_vcpu *vcpu, u32 *msrpm,
>  	write ? clear_bit(bit_write, &tmp) : set_bit(bit_write, &tmp);
>  
>  	msrpm[offset] = tmp;
> +
> +	hv_vmcb_dirty_nested_enlightenments(vcpu);
> +
>  }
>  
>  void set_msr_interception(struct kvm_vcpu *vcpu, u32 *msrpm, u32 msr,
> @@ -1135,6 +1159,9 @@ static void hv_init_vmcb(struct vmcb *vmcb)
>  	if (npt_enabled &&
>  	    ms_hyperv.nested_features & HV_X64_NESTED_ENLIGHTENED_TLB)
>  		hve->hv_enlightenments_control.enlightened_npt_tlb = 1;
> +
> +	if (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)
> +		hve->hv_enlightenments_control.msr_bitmap = 1;
>  }
>  #else
>  static inline void hv_init_vmcb(struct vmcb *vmcb)

-- 
Vitaly