linux-kernel - Re: [PATCH v7 09/20] x86/virt/tdx: Get information about TDX module and TDX-capable memory

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Message-ID: <d55cb607566e43ea6522f0aeb6fe7c10628dd950.camel@intel.com>
Date:   Fri, 2 Dec 2022 21:56:49 +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>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "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 09/20] x86/virt/tdx: Get information about TDX module
 and TDX-capable memory

On Fri, 2022-12-02 at 09:06 -0800, Dave Hansen wrote:
> On 12/2/22 03:11, Huang, Kai wrote:
> > And also to address you concern that not all 892 bytes are reserved, how about
> > below:
> > 
> >         union {
> > -               struct cpuid_config     cpuid_configs[0];
> > -               u8                      reserved5[892];
> > +               DECLARE_FLEX_ARRAY(struct cpuid_config, cpuid_configs);
> > +               u8 padding[892];
> >         };
> >  } __packed __aligned(TDSYSINFO_STRUCT_ALIGNMENT);
> > 
> > The goal is to make the size of 'struct tdsysinfo_struct' to be 1024B so we can
> > use a static variable for it, and at the meantime, it can still have 1024B
> > (enough space) for the TDH.SYS.INFO to write to.
> 
> I just don't like the open-coded sizes.
> 
> For instance, wouldn't it be great if you didn't have to know the size
> of *ANYTHING* else to properly size the '892'?
> 
> Maybe we just need some helpers to hide the gunk:
> 
> #define DECLARE_PADDED_STRUCT(type, name, alignment) 	\
> struct type##_padded {					\
> 	union {						\
> 		struct type name;			\
> 		u8 padding[alignment];			\
> 	}						\
> } name##_padded;
> 
> #define PADDED_STRUCT(name)	(name##_padded.name)
> 
> That can get used like this:
> 
> DECLARE_PADDED_STRUCT(struct tdsysinfo_struct, tdsysinfo,
> 		      TDSYSINFO_STRUCT_ALIGNMENT);
> 
> 
> 	struct tdsysinfo_struct sysinfo = PADDED_STRUCT(tdsysinfo)

Thanks.  Will try out this way.