linux-kernel - Re: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory

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Message-ID: <Y33oCuQtLrFugMFc@hirez.programming.kicks-ass.net>
Date:   Wed, 23 Nov 2022 10:29:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, seanjc@...gle.com,
        pbonzini@...hat.com, dan.j.williams@...el.com,
        rafael.j.wysocki@...el.com, kirill.shutemov@...ux.intel.com,
        ying.huang@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, tony.luck@...el.com, ak@...ux.intel.com,
        isaku.yamahata@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, bagasdotme@...il.com,
        sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when
 initializing TDX module as TDX memory

On Tue, Nov 22, 2022 at 04:21:38PM -0800, Dave Hansen wrote:
> > +	/*
> > +	 * All memory regions that can be used by the TDX module must be
> > +	 * passed to the TDX module during the module initialization.
> > +	 * Once this is done, all "TDX-usable" memory regions are fixed
> > +	 * during module's runtime.
> > +	 *
> > +	 * The initial support of TDX guests only allocates memory from
> > +	 * the global page allocator.  To keep things simple, for now
> > +	 * just make sure all pages in the page allocator are TDX memory.
> > +	 *
> > +	 * To achieve this, use all system memory in the core-mm at the
> > +	 * time of initializing the TDX module as TDX memory, and at the
> > +	 * meantime, reject any new memory in memory hot-add.
> > +	 *
> > +	 * This works as in practice, all boot-time present DIMM is TDX
> > +	 * convertible memory.  However if any new memory is hot-added
> > +	 * before initializing the TDX module, the initialization will
> > +	 * fail due to that memory is not covered by CMR.
> > +	 *
> > +	 * This can be enhanced in the future, i.e. by allowing adding or
> > +	 * onlining non-TDX memory to a separate node, in which case the
> > +	 * "TDX-capable" nodes and the "non-TDX-capable" nodes can exist
> > +	 * together -- the userspace/kernel just needs to make sure pages
> > +	 * for TDX guests must come from those "TDX-capable" nodes.
> > +	 *
> > +	 * Build the list of TDX memory regions as mentioned above so
> > +	 * they can be passed to the TDX module later.
> > +	 */
> 
> This is msotly Documentation/, not a code comment.  Please clean it up.

So personally, I *vastly* prefer code comments over this Documentation/
cesspit. Putting things in Documentation/ is a bit like an
old-folks-home, neatly out of the way to (bit)rot in peace.

And that whole .rst disease is making it unreadable for anybody that
still knows how to use a text editor :-(