linux-kernel - Re: [PATCH] KVM: VMX: Explicitly check for hv_remote_flush

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Date:   Fri, 25 Sep 2020 11:59:00 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.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
Subject: Re: [PATCH] KVM: VMX: Explicitly check for hv_remote_flush_tlb when loading pgd()

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Explicitly check that kvm_x86_ops.tlb_remote_flush() points at Hyper-V's
> implementation for PV flushing instead of assuming that a non-NULL
> implementation means running on Hyper-V.  Wrap the related logic in
> ifdeffery as hv_remote_flush_tlb() is defined iff CONFIG_HYPERV!=n.
>
> Short term, the explicit check makes it more obvious why a non-NULL
> tlb_remote_flush() triggers EPTP shenanigans.  Long term, this will
> allow TDX to define its own implementation of tlb_remote_flush() without
> running afoul of Hyper-V.
>
> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 7 +++++--
>  arch/x86/kvm/vmx/vmx.h | 2 ++
>  2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 6f9a0c6d5dc5..a56fa9451b84 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3073,14 +3073,15 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long pgd,
>  		eptp = construct_eptp(vcpu, pgd, pgd_level);
>  		vmcs_write64(EPT_POINTER, eptp);
>  
> -		if (kvm_x86_ops.tlb_remote_flush) {
> +#if IS_ENABLED(CONFIG_HYPERV)
> +		if (kvm_x86_ops.tlb_remote_flush == hv_remote_flush_tlb) {
>  			spin_lock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>  			to_vmx(vcpu)->ept_pointer = eptp;
>  			to_kvm_vmx(kvm)->ept_pointers_match
>  				= EPT_POINTERS_CHECK;
>  			spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>  		}
> -
> +#endif
>  		if (!enable_unrestricted_guest && !is_paging(vcpu))
>  			guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr;
>  		else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
> @@ -6956,7 +6957,9 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
>  
>  static int vmx_vm_init(struct kvm *kvm)
>  {
> +#if IS_ENABLED(CONFIG_HYPERV)
>  	spin_lock_init(&to_kvm_vmx(kvm)->ept_pointer_lock);
> +#endif
>  
>  	if (!ple_gap)
>  		kvm->arch.pause_in_guest = true;
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index d7ec66db5eb8..51107b7309bc 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -316,8 +316,10 @@ struct kvm_vmx {
>  	bool ept_identity_pagetable_done;
>  	gpa_t ept_identity_map_addr;
>  
> +#if IS_ENABLED(CONFIG_HYPERV)
>  	enum ept_pointers_status ept_pointers_match;
>  	spinlock_t ept_pointer_lock;
> +#endif

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

In case ept_pointers_match/ept_pointer_lock are useless for TDX we may
want to find better names for them to make it clear this is a Hyper-V
thingy (e.g. something like hv_tlb_ept_match/hv_tlb_ept_lock).

>  };
>  
>  bool nested_vmx_allowed(struct kvm_vcpu *vcpu);

-- 
Vitaly