linux-kernel - Re: [PATCH v7 07/20] x86/virt/tdx: Do TDX module global initialization

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Message-ID: <4e3a0a5a44fd4b7a5eef050f43bce0db5bb2d2d5.camel@intel.com>
Date:   Wed, 23 Nov 2022 11:45:08 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "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>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "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>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "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 07/20] x86/virt/tdx: Do TDX module global
 initialization

On Tue, 2022-11-22 at 11:14 -0800, Dave Hansen wrote:
> On 11/20/22 16:26, Kai Huang wrote:
> > The first step of initializing the module is to call TDH.SYS.INIT once
> > on any logical cpu to do module global initialization.  Do the module
> > global initialization.
> > 
> > It also detects the TDX module, as seamcall() returns -ENODEV when the
> > module is not loaded.
> 
> Part of making a good patch set is telling a bit of a story.  In patch
> 4, you laid out 6 steps necessary to initialize TDX.  On top of that,
> there is infrastructure  It would be great to lay that out in a way that
> folks can actually follow along.
> 
> For instance, it would be great to tell the reader here that this patch
> is an inflection point.  It is transitioning out of the infrastructure
> (patches 1->6) and into the actual "multi-steps" of initialization that
> the module spec requires.
> 
> This patch is *TOTALLY* different from the one before it because it
> actually _starts_ to do something useful.
> 
> But, you wouldn't know it from the changelog.

I'll try to enhance the changelog to make them more connected.  Right now I
don't have a clear clue on how to write in best way.

> 
> >  arch/x86/virt/vmx/tdx/tdx.c | 19 +++++++++++++++++--
> >  arch/x86/virt/vmx/tdx/tdx.h |  1 +
> >  2 files changed, 18 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> > index 5db1a05cb4bd..f292292313bd 100644
> > --- a/arch/x86/virt/vmx/tdx/tdx.c
> > +++ b/arch/x86/virt/vmx/tdx/tdx.c
> > @@ -208,8 +208,23 @@ static void seamcall_on_each_cpu(struct seamcall_ctx *sc)
> >   */
> >  static int init_tdx_module(void)
> >  {
> > -	/* The TDX module hasn't been detected */
> > -	return -ENODEV;
> > +	int ret;
> > +
> > +	/*
> > +	 * Call TDH.SYS.INIT to do the global initialization of
> > +	 * the TDX module.  It also detects the module.
> > +	 */
> > +	ret = seamcall(TDH_SYS_INIT, 0, 0, 0, 0, NULL, NULL);
> > +	if (ret)
> > +		goto out;
> 
> Please also note that the 0's are all just unused parameters.  They mean
> nothing.

Will add to the comment.

> 
> > +
> > +	/*
> > +	 * Return -EINVAL until all steps of TDX module initialization
> > +	 * process are done.
> > +	 */
> > +	ret = -EINVAL;
> > +out:
> > +	return ret;
> >  }
> 
> It might be a bit unconventional, but can you imagine how well it would
> tell the story if this comment said:
> 
> 	/*
> 	 * TODO:
> 	 *  - Logical-CPU scope initialization (TDH_SYS_INIT_LP)
> 	 *  - Enumerate capabilities and platform configuration
> 	      (TDH_SYS_CONFIG)
> 	 ...
> 	 */
> 
> and then each of the following patches that *did* those things removed
> the TODO line from the list.
> 
> That TODO list could have been added in patch 4.
> 

Thanks for suggestion.  Will do.

I think I can do this to "construct TDMRs" related patches too.