linux-kernel - Re: [PATCH v12 08/22] x86/virt/tdx: Get information about TDX module and TDX-capable memory

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Message-ID: <20230630093443.GE2533791@hirez.programming.kicks-ass.net>
Date:   Fri, 30 Jun 2023 11:34:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "Luck, Tony" <tony.luck@...el.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>,
        "mingo@...hat.com" <mingo@...hat.com>,
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        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "nik.borisov@...e.com" <nik.borisov@...e.com>,
        "hpa@...or.com" <hpa@...or.com>, "Shahar, Sagi" <sagis@...gle.com>,
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        "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>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v12 08/22] x86/virt/tdx: Get information about TDX module
 and TDX-capable memory

On Thu, Jun 29, 2023 at 09:15:39AM +0000, Huang, Kai wrote:

> Sure.  How about below?
> 
> +       /*
> +        * TDH.SYS.INFO writes the TDSYSINFO_STRUCT and the CMR array
> +        * to the buffers provided by the kernel (via RCX and R8
> +        * respectively).  The buffer size of the TDSYSINFO_STRUCT
> +        * (via RDX) and the maximum entries of the CMR array (via R9)
> +        * passed to this SEAMCALL must be at least the size of
> +        * TDSYSINFO_STRUCT and MAX_CMRS respectively.
> +        *
> +        * Upon a successful return, R9 contains the actual entries
> +        * written to the CMR array.
> +        */
>         sysinfo_pa = __pa(sysinfo);
>         cmr_array_pa = __pa(cmr_array);
>         ret = seamcall(TDH_SYS_INFO, sysinfo_pa, TDSYSINFO_STRUCT_SIZE,

> Or should I just repeat the spec like below?

> +       /*
> +        * TDH.SYS.INFO writes the TDSYSINFO_STRUCT and the CMR array
> +        * to the buffers provided by the kernel:
> +        *
> +        * Input:
> +        *  - RCX: The buffer of TDSYSINFO_STRUCT
> +        *  - RDX: The size of the TDSYSINFO_STRUCT buffer, must be at
> +        *         at least the size of TDSYSINFO_STRUCT
> +        *  - R8: The buffer of the CMR array
> +        *  - R9: The entry number of the array, must be at least
> +        *        MAX_CMRS.
> +        *
> +        * Output (successful):
> +        *  - RDX: The actual bytes written to the TDSYSINFO_STRUCT
> +        *         buffer
> +        *  - R9: The actual entries written to the CMR array.
> +        */
>         sysinfo_pa = __pa(sysinfo);
>         cmr_array_pa = __pa(cmr_array);
>         ret = seamcall(TDH_SYS_INFO, sysinfo_pa, TDSYSINFO_STRUCT_SIZE,

Either of them work for me, thanks!

> > SDM doesn't seem to be the place. That doesn't
> > even list TDCALL/SEAMCALL in Volume 2 :-( Let alone describe the magic
> > values.
> > 
> 
> TDX has it's own specs at here:
> 
> https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html
> 
> For this one you can find it in here:
> 
> https://cdrdv2.intel.com/v1/dl/getContent/733568

Yeah, eventually found it. I still think both TDCALL and SEAMCALL should
be listed in SDM Vol.2 instruction listing -- every valid instruction
should be found there IMO.

I also feel strongly that a global ABI should be decided upon for them
and the SDM would be a good place to mention that.  leaving this to
individual calls like now is a giant pain in the rear.

As is, we have TDCALL leaf-0 with a giant regset but every other leaf
has (c,d,8,9) for input and +(10,11) for output. Lets fix that in stone.

Obviously I also very strongly feel any such ABI must not confict with
pre-existing calling conventions -- IOW, using BP is out, must not
happen.