linux-kernel - Re: [PATCH v11 10/20] x86/virt/tdx: Add placeholder to construct TDMRs to cover all TDX memory regions

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Date:   Mon, 12 Jun 2023 02:21:51 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.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>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "Luck, Tony" <tony.luck@...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 v11 10/20] x86/virt/tdx: Add placeholder to construct
 TDMRs to cover all TDX memory regions

On Fri, 2023-06-09 at 01:52 +0300, kirill.shutemov@...ux.intel.com wrote:
> On Mon, Jun 05, 2023 at 02:27:23AM +1200, Kai Huang wrote:
> > @@ -50,6 +51,8 @@ static DEFINE_MUTEX(tdx_module_lock);
> >  /* All TDX-usable memory regions.  Protected by mem_hotplug_lock. */
> >  static LIST_HEAD(tdx_memlist);
> >  
> > +static struct tdmr_info_list tdx_tdmr_list;
> > +
> >  /*
> >   * Wrapper of __seamcall() to convert SEAMCALL leaf function error code
> >   * to kernel error code.  @seamcall_ret and @out contain the SEAMCALL
> 
> The name is misleading. It is not list, it is an array.

I followed Dave's suggestion in v7:

https://lore.kernel.org/lkml/d84ad1d2-83f9-dab5-5639-8d71f382e3ff@intel.com/

Quote the relevant part here:

"
> +static struct tdmr_info *tdmr_array_entry(struct tdmr_info *tdmr_array,
> +					  int idx)
> +{
> +	return (struct tdmr_info *)((unsigned long)tdmr_array +
> +			cal_tdmr_size() * idx);
> +}

FWIW, I think it's probably a bad idea to have 'struct tdmr_info *'
types floating around since:

	tmdr_info_array[0]

works, but:

	tmdr_info_array[1]

will blow up in your face.  It would almost make sense to have

struct tdmr_info_list {
	struct tdmr_info *first_tdmr;
}

and then pass around pointers to the 'struct tdmr_info_list'.  Maybe
that's overkill, but it is kinda silly to call something an array if []
doesn't work on it.
"

Personally I think it's also fine to use 'list' (e.g., we can also interpret the
name from "English language"'s perspective).

Hi Dave,

Should I change the name to "tdmr_info_array"?


> 
> 
> ...
> 
> > @@ -112,6 +135,15 @@ struct tdx_memblock {
> >  	unsigned long end_pfn;
> >  };
> >  
> > +struct tdmr_info_list {
> > +	void *tdmrs;	/* Flexible array to hold 'tdmr_info's */
> > +	int nr_consumed_tdmrs;	/* How many 'tdmr_info's are in use */
> > +
> > +	/* Metadata for finding target 'tdmr_info' and freeing @tdmrs */
> > +	int tdmr_sz;	/* Size of one 'tdmr_info' */
> > +	int max_tdmrs;	/* How many 'tdmr_info's are allocated */
> > +};
> > +
> >  struct tdx_module_output;
> >  u64 __seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
> >  	       struct tdx_module_output *out);
> 
> Otherwise, looks okay.
> 
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>