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

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Message-ID: <58df22aa-5d2c-f99f-6dfb-9a8b4260dc21@redhat.com>
Date:   Thu, 8 Apr 2021 17:47:15 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vineeth Pillai <viremana@...ux.microsoft.com>,
        Lan Tianyu <Tianyu.Lan@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.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:     "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

On 07/04/21 16:41, Vineeth Pillai wrote:
>   
> +#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);
> +}

In addition to what Vitaly said, can svm->vmcb really be NULL?  If so it 
might be better to reorder initializations and skip the NULL check.

Paolo