linux-kernel - Re: [RFC PATCH 08/21] KVM: x86: Add kvm_x86

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Date:   Mon, 29 Jul 2019 20:08:51 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFC PATCH 08/21] KVM: x86: Add kvm_x86_ops hook to short
 circuit emulation

On Fri, Jul 26, 2019 at 10:52:01PM -0700, Sean Christopherson wrote:
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 48c865a4e5dd..0fb8b60eb136 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -7115,10 +7115,25 @@ static int nested_enable_evmcs(struct kvm_vcpu *vcpu,
>  	return -ENODEV;
>  }
>  
> -static bool svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
> +static bool svm_is_emulatable(struct kvm_vcpu *vcpu, void *insn, int insn_len)
>  {
>  	bool is_user, smap;
>  
> +	if (likely(!insn || insn_len))
> +		return true;
> +
> +	/*
> +	 * Under certain conditions insn_len may be zero on #NPF.  This can
> +	 * happen if a guest gets a page-fault on data access but the HW table
> +	 * walker is not able to read the instruction page (e.g instruction
> +	 * page is not present in memory). In those cases we simply restart the
> +	 * guest, with the exception of AMD Erratum 1096 which is unrecoverable.
> +	 */
> +	if (unlikely(insn && !insn_len)) {
> +		if (!kvm_x86_ops->need_emulation_on_page_fault(vcpu))
> +			return 1;
> +	}

Doh, obviously forgot to compile for SVM when rebasing.