linux-kernel - Re: [PATCH] x86/sgx: Declare sgx_set_attribute() for !CONFIG_X86

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Message-ID: <a43d34d5-623f-20f3-c29a-56985d5614ba@redhat.com>
Date:   Mon, 6 Sep 2021 10:35:31 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Tony Luck <tony.luck@...el.com>, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] x86/sgx: Declare sgx_set_attribute() for !CONFIG_X86_SGX

On 03/09/21 17:58, Jarkko Sakkinen wrote:
>> Eh, it doesn't really simplify the usage.  If anything it makes it more convoluted
>> because the capability check in kvm_vm_ioctl_check_extension() still needs an
>> #ifdef, e.g. readers will wonder why the check is conditional but the usage is not.
> It does objectively a bit, since it's one ifdef less.

But you're effectively replacing #ifdef CONFIG_X86_SGX_KVM with #ifdef 
CONFIG_X86_SGX; so the patch is not a no-op as far as KVM is concerned.

So NACK for the KVM parts (yeah I know it's RFC but just to be clearer), 
but I agree that adding a stub inline version of the function is 
standard practice and we do it a lot in KVM too.

Paolo

> This is fairly standard practice to do in kernel APIs, used in countless
> places, for instance in Tony's patch set to add MCE recovery for SGX. And
> it would be nice to share common pattern here how we define API now and
> futre.
> 
> I also remarked that declaration of "sgx_provisioning_allowed" is not flagged,
> which is IMHO even more convolved because without SGX it is spare data.