linux-kernel - Re: [RFC v2-fix-v1 1/1] x86/tdx: Add __tdx_module_call() and __tdx

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Message-ID: <77545da6-d534-e4c2-a60b-085705e3f0b7@linux.intel.com>
Date:   Wed, 19 May 2021 13:49:00 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2-fix-v1 1/1] x86/tdx: Add __tdx_module_call() and
 __tdx_hypercall() helper functions


On 5/19/2021 1:09 PM, Sean Christopherson wrote:
> On Wed, May 19, 2021, Kuppuswamy, Sathyanarayanan wrote:
>> On 5/19/21 8:31 AM, Dave Hansen wrote:
>>> Was this "older compiler" argument really the reason?
>> It is a speculation. I haven't tried to reproduce it with old compiler. So
>> I have removed that point.
> It's not "older" compilers.  gcc does not support R8-R15 as input/output
> constraints,

Yes that's true, but they can be in clobbers. So it usually just needs a 
mov from the input arguments for output, or a mov to the output 
arguments for output.