linux-kernel - Re: [PATCH v5 0/8] TDX host: metadata reading tweaks, bug fix and info dump

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Message-ID: <CABgObfYXUxqQV_FoxKjC8U3t5DnyM45nz5DpTxYZv2x_uFK_Kw@mail.gmail.com>
Date: Tue, 15 Oct 2024 18:29:47 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Kai Huang <kai.huang@...el.com>, kirill.shutemov@...ux.intel.com, 
	tglx@...utronix.de, bp@...en8.de, peterz@...radead.org, mingo@...hat.com, 
	hpa@...or.com, dan.j.williams@...el.com, seanjc@...gle.com, x86@...nel.org, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, rick.p.edgecombe@...el.com, 
	isaku.yamahata@...el.com, adrian.hunter@...el.com, nik.borisov@...e.com
Subject: Re: [PATCH v5 0/8] TDX host: metadata reading tweaks, bug fix and
 info dump

On Tue, Oct 15, 2024 at 5:30 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> I'm having one of those "I hate this all" moments.  Look at what we say
> in the code:
>
> >   * See the "global_metadata.json" in the "TDX 1.5 ABI definitions".
>
> Basically step one in verifying that this is all right is: Hey, humans,
> please go parse a machine-readable format.  That's insanity.  If Intel
> wants to publish JSON as the canonical source of truth, that's fine.
> It's great, actually.  But let's stop playing human JSON parser and make
> the computers do it for us, OK?
>
> Let's just generate the code.  Basically, as long as the generated C is
> marginally readable, I'm OK with it.  The most important things are:
>
>  1. Adding a field is dirt simple
>  2. Using the generated C is simple
>
> In 99% of the cases, nobody ends up having to ever look at the generated
> code.
>
> Take a look at the attached python program and generated C file.  I
> think they qualify.  We can check the script into tools/scripts/ and it
> can get re-run when new json comes out or when a new field is needed.
> You'd could call the generated code like this:

Ok, so let's move this thing forward. Here is a more polished script
and the output. Untested beyond compilation.

Kai, feel free to include it in v6 with my

Signed-off-by: Paolo Bonzini <pbonzini@...hat.om>

I made an attempt at adding array support and using it with the CMR
information; just to see if Intel is actually trying to make
global_metadata.json accurate. The original code has

  for (i = 0; i < sysinfo_cmr->num_cmrs; i++) {
    READ_SYS_INFO(CMR_BASE + i, cmr_base[i]);
    READ_SYS_INFO(CMR_SIZE + i, cmr_size[i]);
  }

The generated code instead always tries to read 32 fields and returns
non-zero from get_tdx_sys_info_cmr if they are missing. If it fails to
read the fields above NUM_CMRS, just remove that part of the tdx.py
script and make sure that a comment in the code shames the TDX ABI
documentation adequately. :)

Thanks,

Paolo

View attachment "tdx-generated.c" of type "text/x-csrc" (2046 bytes)

View attachment "tdx-generated.h" of type "text/x-chdr" (547 bytes)

View attachment "tdx.py" of type "text/x-python" (3350 bytes)