On 7/08/24 15:09, Huang, Kai wrote: > On Mon, 2024-08-05 at 18:13 -0700, Dan Williams wrote: >> Huang, Kai wrote: >> [..] >>>> The unrolled loop is the same amount of work as maintaining @fields. >>> >>> Hi Dan, >>> >>> Thanks for the feedback. >>> >>> AFAICT Dave didn't like this way: >>> >>> https://lore.kernel.org/lkml/cover.1699527082.git.kai.huang@xxxxxxxxx/T/#me6f615d7845215c278753b57a0bce1162960209d >> >> I agree with Dave that the original was unreadable. However, I also >> think he glossed over the loss of type-safety and the silliness of >> defining an array to precisely map fields only to turn around and do a >> runtime check that the statically defined array was filled out >> correctly. So I think lets solve the readability problem *and* make the >> array definition identical in appearance to unrolled type-safe >> execution, something like (UNTESTED!): >> >> > [...] > >> +/* >> + * Assumes locally defined @ret and @ts to convey the error code and the >> + * 'struct tdx_tdmr_sysinfo' instance to fill out >> + */ >> +#define TD_SYSINFO_MAP(_field_id, _offset) \ >> + ({ \ >> + if (ret == 0) \ >> + ret = read_sys_metadata_field16( \ >> + MD_FIELD_ID_##_field_id, &ts->_offset); \ >> + }) >> + > > We need to support u16/u32/u64 metadata field sizes, but not just u16. > > E.g.: > > struct tdx_sysinfo_module_info { > u32 sys_attributes; > u64 tdx_features0; > }; > > has both u32 and u64 in one structure. > > To achieve type-safety for all field sizes, I think we need one helper > for each field size. E.g., > > #define READ_SYSMD_FIELD_FUNC(_size) \ > static inline int \ > read_sys_metadata_field##_size(u64 field_id, u##_size *data) \ > { \ > u64 tmp; \ > int ret; \ > \ > ret = read_sys_metadata_field(field_id, &tmp); \ > if (ret) \ > return ret; \ > \ > *data = tmp; \ > return 0; \ > } > > /* For now only u16/u32/u64 are needed */ > READ_SYSMD_FIELD_FUNC(16) > READ_SYSMD_FIELD_FUNC(32) > READ_SYSMD_FIELD_FUNC(64) > > Is this what you were thinking? > > (Btw, I recall that I tried this before for internal review, but AFAICT > Dave didn't like this.) > > For the build time check as you replied to the next patch, I agree it's > better than the runtime warning check as done in the current code. > > If we still use the type-less 'void *stbuf' function to read metadata > fields for all sizes, then I think we can do below: > > /* > * Read one global metadata field and store the data to a location of a > * given buffer specified by the offset and size (in bytes). > */ > static int stbuf_read_sysmd_field(u64 field_id, void *stbuf, int offset, > int size) > { > void *member = stbuf + offset; > u64 tmp; > int ret; > > ret = read_sys_metadata_field(field_id, &tmp); > if (ret) > return ret; > > memcpy(member, &tmp, size); > > return 0; > } > > /* Wrapper to read one metadata field to u8/u16/u32/u64 */ > #define stbuf_read_sysmd_single(_field_id, _pdata) \ > stbuf_read_sysmd_field(_field_id, _pdata, 0, \ > sizeof(typeof(*(_pdata)))) > > #define CHECK_MD_FIELD_SIZE(_field_id, _st, _member) \ > BUILD_BUG_ON(MD_FIELD_ELE_SIZE(MD_FIELD_ID_##_field_id) != \ > sizeof(_st->_member)) > > #define TD_SYSINFO_MAP_TEST(_field_id, _st, _member) \ > ({ \ > if (ret) { \ > CHECK_MD_FIELD_SIZE(_field_id, _st, _member); \ > ret = stbuf_read_sysmd_single( \ > MD_FIELD_ID_##_field_id, \ > &_st->_member); \ > } \ > }) > > static int get_tdx_module_info(struct tdx_sysinfo_module_info *modinfo) > { > int ret = 0; > > #define TD_SYSINFO_MAP_MOD_INFO(_field_id, _member) \ > TD_SYSINFO_MAP_TEST(_field_id, modinfo, _member) > > TD_SYSINFO_MAP_MOD_INFO(SYS_ATTRIBUTES, sys_attributes); > TD_SYSINFO_MAP_MOD_INFO(TDX_FEATURES0, tdx_features0); > > return ret; > } > > With the build time check above, I think it's OK to lose the type-safe > inside the stbuf_read_sysmd_field(), and the code is simpler IMHO. > > Any comments? BUILD_BUG_ON() requires a function, but it is still be possible to add a build time check in TD_SYSINFO_MAP e.g. #define TD_SYSINFO_CHECK_SIZE(_field_id, _size) \ __builtin_choose_expr(MD_FIELD_ELE_SIZE(_field_id) == _size, _size, (void)0) #define _TD_SYSINFO_MAP(_field_id, _offset, _size) \ { .field_id = _field_id, \ .offset = _offset, \ .size = TD_SYSINFO_CHECK_SIZE(_field_id, _size) } #define TD_SYSINFO_MAP(_field_id, _struct, _member) \ _TD_SYSINFO_MAP(MD_FIELD_ID_##_field_id, \ offsetof(_struct, _member), \ sizeof(typeof(((_struct *)0)->_member)))
