linux-kernel - Re: [PATCH v5 09/12] x86/tdx: Wire up KVM hypercalls

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Message-ID: <b4742f7b-b1d8-8431-407f-f15a78a0d3f0@linux.intel.com>
Date:   Tue, 24 Aug 2021 12:11:00 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 09/12] x86/tdx: Wire up KVM hypercalls



On 8/24/21 11:29 AM, Borislav Petkov wrote:
> On Tue, Aug 24, 2021 at 11:11:43AM -0700, Kuppuswamy, Sathyanarayanan wrote:
>> Since TDX code can be used by other hypervisor (non KVM case) we
>> want to have a config to differentiate the KVM related calls.
> 
> You need to start explaining yourself better. WTH does "to differentiate
> the KVM related calls" even mean? Differentiate for what?!

tdx_kvm_hypercall() function and its usage in arch/x86/include/asm/kvm_para.h
is only required for KVM hypervisor.

  static inline long kvm_hypercall0(unsigned int nr)
  {
         long ret;
+
+       if (prot_guest_has(PATTR_GUEST_TDX))
+               return tdx_kvm_hypercall(nr, 0, 0, 0, 0);

If the TDX code is complied for another hypervior, we need some config to
disable above the above code. CONFIG_INTEL_TDX_GUEST_KVM is added
for this purpose. If you think there is no sufficient reason, I can
use defined(CONFIG_KVM_GUEST) && defined(CONFIG_INTEL_TDX_GUEST) to protect
the implementation of tdx_kvm_hypercall()


> 
> Our CONFIG space is a huuge mess. Adding another option better be
> properly justified.
> 
>> Compiler raised version generation issue for __tdx_hypercall
> 
> -ENOTENOUGHINFO.

Following is the error info.

WARNING: modpost: EXPORT symbol "__tdx_hypercall" [vmlinux] version generation failed, symbol will 
not be versioned.

So to fix the above issue, added tdx.h in arch/x86/include/asm/asm-prototypes.h

> 
> Try again.
> 
>> Yes. I will fix this in next version.
> 
> And here audit all your patchsets. All exports better be _GPL.

Ok. I will check it before my next submission.

> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer