linux-kernel - Re: [RFC v2 10/32] x86/tdx: Wire up KVM hypercalls

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Date:   Thu, 13 May 2021 12:29:18 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [RFC v2 10/32] x86/tdx: Wire up KVM hypercalls



On 5/12/21 7:29 AM, Dave Hansen wrote:
> On 5/12/21 7:10 AM, Kuppuswamy, Sathyanarayanan wrote:
>> On 5/12/21 6:00 AM, Kirill A. Shutemov wrote:
>>> This has to be compiled only for TDX+KVM.
>>
>> Got it. So if we want to remove the "C" file include, we will have to
>> add #ifdef CONFIG_KVM_GUEST in Makefile.
>>
>> ifdef CONFIG_KVM_GUEST
>> obj-$(CONFIG_INTEL_TDX_GUEST) += tdx-kvm.o
>> #endif
> 
> Is there truly no dependency between CONFIG_KVM_GUEST and
> CONFIG_INTEL_TDX_GUEST?

We want to re-use TDX code with other hypervisors/guests as well. So
we can't create direct dependency with CONFIG_KVM_GUEST in Kconfig.

> 
> If there isn't, then the way we do it is adding another (invisible)
> Kconfig variable to express the dependency for tdx-kvm.o:
> 
> config INTEL_TDX_GUEST_KVM
> 	bool
> 	depends on KVM_GUEST && INTEL_TDX_GUEST

Currently it will only be used for KVM hypercall code. Will it to be
overkill to create a new config over #ifdefs for this use case ? But,
if this is the preferred approach, I will go with this suggestion.

> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer