linux-kernel - Re: [PATCH 1/8] KVM: SVM: extract VMCB accessors to a new file

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Date:   Mon, 7 Nov 2022 17:08:51 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        nathan@...nel.org, thomas.lendacky@....com,
        andrew.cooper3@...rix.com, peterz@...radead.org,
        jmattson@...gle.com, stable@...r.kernel.org
Subject: Re: [PATCH 1/8] KVM: SVM: extract VMCB accessors to a new file

On Mon, Nov 07, 2022, Paolo Bonzini wrote:
> Having inline functions confuses the compilation of asm-offsets.c,
> which cannot find kvm_cache_regs.h because arch/x86/kvm is not in
> asm-offset.c's include path.  Just extract the functions to a
> new file.
> 
> No functional change intended.
> 
> Cc: stable@...r.kernel.org
> Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/svm/avic.c         |   1 +
>  arch/x86/kvm/svm/nested.c       |   1 +
>  arch/x86/kvm/svm/sev.c          |   1 +
>  arch/x86/kvm/svm/svm.c          |   1 +
>  arch/x86/kvm/svm/svm.h          | 200 ------------------------------
>  arch/x86/kvm/svm/svm_onhyperv.c |   1 +
>  arch/x86/kvm/svm/vmcb.h         | 211 ++++++++++++++++++++++++++++++++

I don't think vmcb.h is a good name.  The logical inclusion sequence would be for
svm.h to include vmcb.h, e.g. SVM requires knowledge about VMCBs, but this requires
vmcb.h to include svm.h to dereference "struct vcpu_svm".

Unlike VMX's vmcs.h, the new file isn't a "pure" VMCB helper, it also holds a
decent amount of KVM's SVM logic.

What about making KVM self-sufficient?  The includes in asm-offsets.c are quite
ugly

 #include "../kvm/vmx/vmx.h"
 #include "../kvm/svm/svm.h"

or as a stopgap to make backporting easier, just include kvm_cache_regs.h?

>  void svm_leave_nested(struct kvm_vcpu *vcpu);
> diff --git a/arch/x86/kvm/svm/svm_onhyperv.c b/arch/x86/kvm/svm/svm_onhyperv.c
> index 8cdc62c74a96..ae0a101329e6 100644
> --- a/arch/x86/kvm/svm/svm_onhyperv.c
> +++ b/arch/x86/kvm/svm/svm_onhyperv.c
> @@ -8,6 +8,7 @@
>  #include <asm/mshyperv.h>
>  
>  #include "svm.h"
> +#include "vmcb.h"
>  #include "svm_ops.h"
>  
>  #include "hyperv.h"
> diff --git a/arch/x86/kvm/svm/vmcb.h b/arch/x86/kvm/svm/vmcb.h
> new file mode 100644
> index 000000000000..8757cda27e3a
> --- /dev/null
> +++ b/arch/x86/kvm/svm/vmcb.h
> @@ -0,0 +1,211 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Kernel-based Virtual Machine driver for Linux
> + *
> + * AMD SVM support - VMCB accessors
> + */
> +
> +#ifndef __SVM_VMCB_H
> +#define __SVM_VMCB_H
> +
> +#include "kvm_cache_regs.h"

This should include "svm.h" instead of relying on the parent to include said file.