linux-kernel - Re: [PATCH 5/8] KVM: nSVM: implement ondemand allocation of the nested state

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Message-ID: <476eecc8-a861-203c-40f5-46707d8c0237@redhat.com>
Date:   Thu, 20 Aug 2020 11:58:41 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH 5/8] KVM: nSVM: implement ondemand allocation of the
 nested state

On 20/08/20 11:13, Maxim Levitsky wrote:
> @@ -3912,6 +3914,14 @@ static int svm_pre_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
>  	vmcb_gpa = GET_SMSTATE(u64, smstate, 0x7ee0);
>  
>  	if (guest) {
> +		/*
> +		 * This can happen if SVM was not enabled prior to #SMI,
> +		 * but guest corrupted the #SMI state and marked it as
> +		 * enabled it there
> +		 */
> +		if (!svm->nested.initialized)
> +			return 1;
> +
>  		if (kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(vmcb_gpa), &map) == -EINVAL)
>  			return 1;

This can also happen if you live migrate while in SMM (EFER.SVME=0).
You need to check for the SVME bit in the SMM state save area, and:

1) triple fault if it is clear

2) call svm_allocate_nested if it is set.

Paolo