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

[Paolo Bonzini]

On 11/7/22 18:08, Sean Christopherson wrote:
> 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@xxxxxxxxxxxxxxx
> > Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > ---
> >   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.

Yes, it's basically the wrappers that KVM uses to access the VMCB fields.

> What about making KVM self-sufficient?

You mean having a different asm-offsets.h file just for arch/x86/kvm/?

> 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?

The problem is that the _existing_ include of kvm_cache_regs.h in svm.h 
fails, with

arch/x86/kernel/../kvm/svm/svm.h:25:10: fatal error: kvm_cache_regs.h: 
No such file or directory
   25 | #include "kvm_cache_regs.h"
      |          ^~~~~~~~~~~~~~~~~~
compilation terminated.

The other two solutions here are:

1) move kvm_cache_regs.h to arch/x86/include/asm/ so it can be included 
normally

2) extract the structs to arch/x86/kvm/svm/svm_types.h and include that 
from asm-offsets.h, basically the opposite of this patch.

(2) is my preference if having a different asm-offsets.h file turns out 
to be too complex.  We can do the same for VMX as well.

Paolo

> >   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.