linux-kernel - Re: [PATCH v2] KVM: x86: Modify struct kvm_nested

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Message-Id: <D2867F96-6B8D-4A1D-9F6F-CF0F171614BC@oracle.com>
Date:   Wed, 19 Jun 2019 01:36:25 +0300
From:   Liran Alon <liran.alon@...cle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Modify struct kvm_nested_state to have
 explicit fields for data



> On 18 Jun 2019, at 19:24, Paolo Bonzini <pbonzini@...hat.com> wrote:
> 
> From: Liran Alon <liran.alon@...cle.com>
> 
> Improve the KVM_{GET,SET}_NESTED_STATE structs by detailing the format
> of VMX nested state data in a struct.
> 
> In order to avoid changing the ioctl values of
> KVM_{GET,SET}_NESTED_STATE, there is a need to preserve
> sizeof(struct kvm_nested_state). This is done by defining the data
> struct as "data.vmx[0]". It was the most elegant way I found to
> preserve struct size while still keeping struct readable and easy to
> maintain. It does have a misfortunate side-effect that now it has to be
> accessed as "data.vmx[0]" rather than just "data.vmx".
> 
> Because we are already modifying these structs, I also modified the
> following:
> * Define the "format" field values as macros.
> * Rename vmcs_pa to vmcs12_pa for better readability.
> 
> Signed-off-by: Liran Alon <liran.alon@...cle.com>
> [Remove SVM stubs, add KVM_STATE_NESTED_VMX_VMCS12_SIZE. - Paolo]

1) Why should we remove SVM stubs? I think it makes the interface intention more clear.
Do you see any disadvantage of having them?

2) What is the advantage of defining a separate KVM_STATE_NESTED_VMX_VMCS12_SIZE
rather than just moving VMCS12_SIZE to userspace header?

-Liran

> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---