linux-kernel - Re: [PATCH 7/7] KVM: SVM: hyper-v: Direct Virtual Flush support

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Message-ID: <87a6q9augt.fsf@vitty.brq.redhat.com>
Date:   Thu, 08 Apr 2021 13:25:54 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Vineeth Pillai <viremana@...ux.microsoft.com>
Cc:     "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,
        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>
Subject: Re: [PATCH 7/7] KVM: SVM: hyper-v: Direct Virtual Flush support

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

> From Hyper-V TLFS:
>  "The hypervisor exposes hypercalls (HvFlushVirtualAddressSpace,
>   HvFlushVirtualAddressSpaceEx, HvFlushVirtualAddressList, and
>   HvFlushVirtualAddressListEx) that allow operating systems to more
>   efficiently manage the virtual TLB. The L1 hypervisor can choose to
>   allow its guest to use those hypercalls and delegate the responsibility
>   to handle them to the L0 hypervisor. This requires the use of a
>   partition assist page."
>
> Add the Direct Virtual Flush support for SVM.
>
> Related VMX changes:
> commit 6f6a657c9998 ("KVM/Hyper-V/VMX: Add direct tlb flush support")
>
> Signed-off-by: Vineeth Pillai <viremana@...ux.microsoft.com>
> ---
>  arch/x86/kvm/svm/svm.c | 48 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 3562a247b7e8..c6d3f3a7c986 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -440,6 +440,32 @@ static void svm_init_osvw(struct kvm_vcpu *vcpu)
>  		vcpu->arch.osvw.status |= 1;
>  }
>  
> +#if IS_ENABLED(CONFIG_HYPERV)
> +static int hv_enable_direct_tlbflush(struct kvm_vcpu *vcpu)
> +{
> +	struct hv_enlightenments *hve;
> +	struct hv_partition_assist_pg **p_hv_pa_pg =
> +			&to_kvm_hv(vcpu->kvm)->hv_pa_pg;
> +
> +	if (!*p_hv_pa_pg)
> +		*p_hv_pa_pg = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +
> +	if (!*p_hv_pa_pg)
> +		return -ENOMEM;
> +
> +	hve = (struct hv_enlightenments *)&to_svm(vcpu)->vmcb->hv_enlightenments;
> +
> +	hve->partition_assist_page = __pa(*p_hv_pa_pg);
> +	hve->hv_vm_id = (unsigned long)vcpu->kvm;
> +	if (!hve->hv_enlightenments_control.nested_flush_hypercall) {
> +		hve->hv_enlightenments_control.nested_flush_hypercall = 1;
> +		vmcb_mark_dirty(to_svm(vcpu)->vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS);
> +	}
> +
> +	return 0;
> +}
> +#endif
> +
>  static int has_svm(void)
>  {
>  	const char *msg;
> @@ -1034,6 +1060,21 @@ static __init int svm_hardware_setup(void)
>  		svm_x86_ops.tlb_remote_flush_with_range =
>  				kvm_hv_remote_flush_tlb_with_range;
>  	}
> +
> +	if (ms_hyperv.nested_features & HV_X64_NESTED_DIRECT_FLUSH) {
> +		pr_info("kvm: Hyper-V Direct TLB Flush enabled\n");
> +		for_each_online_cpu(cpu) {
> +			struct hv_vp_assist_page *vp_ap =
> +				hv_get_vp_assist_page(cpu);
> +
> +			if (!vp_ap)
> +				continue;
> +
> +			vp_ap->nested_control.features.directhypercall = 1;
> +		}
> +		svm_x86_ops.enable_direct_tlbflush =
> +				hv_enable_direct_tlbflush;
> +	}
>  #endif
>  
>  	if (nrips) {
> @@ -3913,6 +3954,13 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
>  	}
>  	svm->vmcb->save.cr2 = vcpu->arch.cr2;
>  
> +#if IS_ENABLED(CONFIG_HYPERV)
> +	if (svm->vmcb->hv_enlightenments.hv_vp_id != to_hv_vcpu(vcpu)->vp_index) {

This looks wrong (see my previous comment about mixing KVM-on-Hyper-V
and Windows/Hyper-V-on-KVM). 'to_hv_vcpu(vcpu)->vp_index' is
'Windows/Hyper-V-on-KVM' thingy, it does not exist when we run without
any Hyper-V enlightenments exposed (e.g. when we run Linux as our
guest).

> +		svm->vmcb->hv_enlightenments.hv_vp_id = to_hv_vcpu(vcpu)->vp_index;
> +		vmcb_mark_dirty(svm->vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS);
> +	}
> +#endif
> +
>  	/*
>  	 * Run with all-zero DR6 unless needed, so that we can get the exact cause
>  	 * of a #DB.

-- 
Vitaly