linux-kernel - Re: [PATCH v7 05/20] x86/virt/tdx: Implement functions to make SEAMCALL

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Date:   Wed, 23 Nov 2022 08:53:30 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v7 05/20] x86/virt/tdx: Implement functions to make
 SEAMCALL

On Tue, 2022-11-22 at 10:06 +0100, Peter Zijlstra wrote:
> On Mon, Nov 21, 2022 at 01:26:27PM +1300, Kai Huang wrote:
> > +/*
> > + * Wrapper of __seamcall() to convert SEAMCALL leaf function error code
> > + * to kernel error code.  @seamcall_ret and @out contain the SEAMCALL
> > + * leaf function return code and the additional output respectively if
> > + * not NULL.
> > + */
> > +static int __always_unused seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
> > +				    u64 *seamcall_ret,
> > +				    struct tdx_module_output *out)
> > +{
> 
> What's the point of a 'static __always_unused' function again? Other
> than to test the DCE pass of a linker, that is?
> 

It is used to avoid the compile warning as so far with this patch it doesn't
have any caller.  Without the __always_unused, the compiler will complain.

Originally it was in the patch "Shut down TDX module in case of error" where it
was firstly called.  Dave suggested to move it out:

https://lore.kernel.org/all/6ed2746d-f44c-4511-7373-5706dd7c3f0f@intel.com/