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

[Dave Hansen]

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)