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

["Huang, Kai" <kai.huang@intel.com>]

On Fri, 2023-06-30 at 11:34 +0200, Peter Zijlstra wrote:
> 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!

I will choose the first one since it's shorter.  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.

Yeah I agree how the specs are organized is not ideal.  We have been having pain
during our development too.

> 
> 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.

Fully agreed.