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

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Message-ID: <3ca5e8b6-c786-2f15-8f81-fd6353c43692@redhat.com>
Date:   Mon, 7 Nov 2022 18:36:21 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.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 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@...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.

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.
>